From e74d49fc8aa3b2943b63b6d3b83add023274bc2e Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Sat, 8 Jun 2019 07:57:25 -0400
Subject: [PATCH] Remove dupe info between ChainSpec and EthSpec

---
 beacon_node/beacon_chain/src/beacon_chain.rs  | 91 ++++++++-----------
 beacon_node/beacon_chain/src/iter.rs          |  7 +-
 beacon_node/client/src/beacon_chain_types.rs  | 18 ++--
 beacon_node/client/src/client_config.rs       |  7 +-
 beacon_node/client/src/lib.rs                 | 11 ++-
 beacon_node/eth2-libp2p/src/behaviour.rs      |  2 +-
 beacon_node/http_server/src/api.rs            |  3 +-
 beacon_node/network/src/sync/simple_sync.rs   | 10 +-
 beacon_node/rpc/src/beacon_node.rs            |  3 +-
 beacon_node/rpc/src/validator.rs              | 10 +-
 beacon_node/src/run.rs                        |  6 +-
 beacon_node/store/src/block_at_slot.rs        |  8 +-
 eth2/fork_choice/benches/benches.rs           |  2 +-
 eth2/fork_choice/examples/example.rs          |  2 +-
 eth2/fork_choice/src/bitwise_lmd_ghost.rs     |  2 +-
 eth2/fork_choice/src/optimized_lmd_ghost.rs   |  2 +-
 eth2/fork_choice/src/slow_lmd_ghost.rs        |  2 +-
 eth2/fork_choice/src/test_utils.rs            |  6 +-
 eth2/fork_choice/tests/tests.rs               |  4 +-
 eth2/operation_pool/src/lib.rs                | 12 +--
 .../benches/bench_epoch_processing.rs         |  6 +-
 eth2/state_processing/benches/benches.rs      |  6 +-
 .../src/per_block_processing.rs               |  4 +-
 .../block_processing_builder.rs               |  8 +-
 .../src/per_block_processing/tests.rs         | 15 +--
 .../validate_attestation.rs                   |  2 +-
 .../verify_proposer_slashing.rs               | 12 +--
 .../per_block_processing/verify_transfer.rs   |  4 +-
 .../src/per_epoch_processing.rs               |  2 +-
 .../src/per_epoch_processing/tests.rs         |  4 +-
 .../validator_statuses.rs                     |  6 +-
 .../src/per_slot_processing.rs                |  2 +-
 eth2/types/src/beacon_state.rs                |  2 +-
 .../src/beacon_state/beacon_state_types.rs    | 45 +++++----
 .../types/src/beacon_state/committee_cache.rs | 17 +++-
 .../src/beacon_state/committee_cache/tests.rs | 28 +++---
 eth2/types/src/beacon_state/tests.rs          | 22 ++---
 eth2/types/src/chain_spec.rs                  | 18 ++--
 .../testing_attestation_data_builder.rs       |  8 +-
 .../builders/testing_beacon_block_builder.rs  | 34 ++++---
 .../builders/testing_beacon_state_builder.rs  |  8 +-
 .../testing_proposer_slashing_builder.rs      |  7 +-
 .../builders/testing_transfer_builder.rs      |  4 +-
 .../src/cases/epoch_processing_crosslinks.rs  |  4 +-
 .../epoch_processing_registry_updates.rs      |  2 +-
 .../src/cases/operations_attester_slashing.rs |  5 +-
 .../ef_tests/src/cases/operations_deposit.rs  |  2 +-
 tests/ef_tests/src/cases/operations_exit.rs   |  4 +-
 .../src/cases/operations_proposer_slashing.rs |  5 +-
 .../ef_tests/src/cases/operations_transfer.rs |  4 +-
 tests/ef_tests/src/cases/shuffling.rs         |  2 +-
 tests/ef_tests/src/eth_specs.rs               |  8 +-
 .../src/attestation_producer/mod.rs           |  4 +-
 validator_client/src/block_producer/mod.rs    | 10 +-
 validator_client/src/config.rs                | 10 +-
 validator_client/src/duties/mod.rs            |  2 +-
 validator_client/src/service.rs               | 17 +++-
 57 files changed, 299 insertions(+), 252 deletions(-)

diff --git a/beacon_node/beacon_chain/src/beacon_chain.rs b/beacon_node/beacon_chain/src/beacon_chain.rs
index a9374aa6a..4d77d7aa5 100644
--- a/beacon_node/beacon_chain/src/beacon_chain.rs
+++ b/beacon_node/beacon_chain/src/beacon_chain.rs
@@ -96,6 +96,7 @@ pub trait BeaconChainTypes {
 /// Represents the "Beacon Chain" component of Ethereum 2.0. Allows import of blocks and block
 /// operations and chooses a canonical head.
 pub struct BeaconChain<T: BeaconChainTypes> {
+    pub spec: ChainSpec,
     /// Persistent storage for blocks, states, etc. Typically an on-disk store, such as LevelDB.
     pub store: Arc<T::Store>,
     /// Reports the current slot, typically based upon the system clock.
@@ -148,6 +149,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         genesis_state.build_all_caches(&spec)?;
 
         Ok(Self {
+            spec,
             store,
             slot_clock,
             op_pool: OperationPool::new(),
@@ -160,7 +162,10 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
     }
 
     /// Attempt to load an existing instance from the given `store`.
-    pub fn from_store(store: Arc<T::Store>) -> Result<Option<BeaconChain<T>>, Error> {
+    pub fn from_store(
+        store: Arc<T::Store>,
+        spec: ChainSpec,
+    ) -> Result<Option<BeaconChain<T>>, Error> {
         let key = Hash256::from_slice(&BEACON_CHAIN_DB_KEY.as_bytes());
         let p: PersistedBeaconChain<T> = match store.get(&key) {
             Err(e) => return Err(e.into()),
@@ -168,8 +173,6 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             Ok(Some(p)) => p,
         };
 
-        let spec = T::EthSpec::spec();
-
         let slot_clock = T::SlotClock::new(
             spec.genesis_slot,
             p.state.genesis_time,
@@ -179,6 +182,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         let fork_choice = T::ForkChoice::new(store.clone());
 
         Ok(Some(BeaconChain {
+            spec,
             store,
             slot_clock,
             op_pool: OperationPool::default(),
@@ -363,10 +367,10 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
             // If required, transition the new state to the present slot.
             for _ in state.slot.as_u64()..present_slot.as_u64() {
-                per_slot_processing(&mut state, &T::EthSpec::spec())?;
+                per_slot_processing(&mut state, &self.spec)?;
             }
 
-            state.build_all_caches(&T::EthSpec::spec())?;
+            state.build_all_caches(&self.spec)?;
 
             state
         };
@@ -400,7 +404,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
     /// Ensures the current canonical `BeaconState` has been transitioned to match the `slot_clock`.
     pub fn catchup_state(&self) -> Result<(), Error> {
-        let spec = &T::EthSpec::spec();
+        let spec = &self.spec;
 
         let present_slot = match self.slot_clock.present_slot() {
             Ok(Some(slot)) => slot,
@@ -426,7 +430,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
     ///
     /// Ideally this shouldn't be required, however we leave it here for testing.
     pub fn ensure_state_caches_are_built(&self) -> Result<(), Error> {
-        self.state.write().build_all_caches(&T::EthSpec::spec())?;
+        self.state.write().build_all_caches(&self.spec)?;
 
         Ok(())
     }
@@ -469,7 +473,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
     /// genesis.
     pub fn slots_since_genesis(&self) -> Option<SlotHeight> {
         let now = self.read_slot_clock()?;
-        let genesis_slot = T::EthSpec::spec().genesis_slot;
+        let genesis_slot = self.spec.genesis_slot;
 
         if now < genesis_slot {
             None
@@ -494,12 +498,12 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
     pub fn block_proposer(&self, slot: Slot) -> Result<usize, BeaconStateError> {
         self.state
             .write()
-            .build_committee_cache(RelativeEpoch::Current, &T::EthSpec::spec())?;
+            .build_committee_cache(RelativeEpoch::Current, &self.spec)?;
 
         let index = self.state.read().get_beacon_proposer_index(
             slot,
             RelativeEpoch::Current,
-            &T::EthSpec::spec(),
+            &self.spec,
         )?;
 
         Ok(index)
@@ -530,7 +534,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
     /// Produce an `AttestationData` that is valid for the present `slot` and given `shard`.
     pub fn produce_attestation_data(&self, shard: u64) -> Result<AttestationData, Error> {
-        let slots_per_epoch = T::EthSpec::spec().slots_per_epoch;
+        let slots_per_epoch = T::EthSpec::slots_per_epoch();
 
         self.metrics.attestation_production_requests.inc();
         let timer = self.metrics.attestation_production_times.start_timer();
@@ -591,9 +595,9 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         self.metrics.attestation_processing_requests.inc();
         let timer = self.metrics.attestation_processing_times.start_timer();
 
-        let result =
-            self.op_pool
-                .insert_attestation(attestation, &*self.state.read(), &T::EthSpec::spec());
+        let result = self
+            .op_pool
+            .insert_attestation(attestation, &*self.state.read(), &self.spec);
 
         if result.is_ok() {
             self.metrics.attestation_processing_successes.inc();
@@ -610,19 +614,19 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         deposit: Deposit,
     ) -> Result<DepositInsertStatus, DepositValidationError> {
         self.op_pool
-            .insert_deposit(deposit, &*self.state.read(), &T::EthSpec::spec())
+            .insert_deposit(deposit, &*self.state.read(), &self.spec)
     }
 
     /// Accept some exit and queue it for inclusion in an appropriate block.
     pub fn process_voluntary_exit(&self, exit: VoluntaryExit) -> Result<(), ExitValidationError> {
         self.op_pool
-            .insert_voluntary_exit(exit, &*self.state.read(), &T::EthSpec::spec())
+            .insert_voluntary_exit(exit, &*self.state.read(), &self.spec)
     }
 
     /// Accept some transfer and queue it for inclusion in an appropriate block.
     pub fn process_transfer(&self, transfer: Transfer) -> Result<(), TransferValidationError> {
         self.op_pool
-            .insert_transfer(transfer, &*self.state.read(), &T::EthSpec::spec())
+            .insert_transfer(transfer, &*self.state.read(), &self.spec)
     }
 
     /// Accept some proposer slashing and queue it for inclusion in an appropriate block.
@@ -630,11 +634,8 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         &self,
         proposer_slashing: ProposerSlashing,
     ) -> Result<(), ProposerSlashingValidationError> {
-        self.op_pool.insert_proposer_slashing(
-            proposer_slashing,
-            &*self.state.read(),
-            &T::EthSpec::spec(),
-        )
+        self.op_pool
+            .insert_proposer_slashing(proposer_slashing, &*self.state.read(), &self.spec)
     }
 
     /// Accept some attester slashing and queue it for inclusion in an appropriate block.
@@ -642,11 +643,8 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         &self,
         attester_slashing: AttesterSlashing,
     ) -> Result<(), AttesterSlashingValidationError> {
-        self.op_pool.insert_attester_slashing(
-            attester_slashing,
-            &*self.state.read(),
-            &T::EthSpec::spec(),
-        )
+        self.op_pool
+            .insert_attester_slashing(attester_slashing, &*self.state.read(), &self.spec)
     }
 
     /// Accept some block and attempt to add it to block DAG.
@@ -708,18 +706,18 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         // Transition the parent state to the block slot.
         let mut state: BeaconState<T::EthSpec> = parent_state;
         for _ in state.slot.as_u64()..block.slot.as_u64() {
-            if let Err(e) = per_slot_processing(&mut state, &T::EthSpec::spec()) {
+            if let Err(e) = per_slot_processing(&mut state, &self.spec) {
                 return Ok(BlockProcessingOutcome::InvalidBlock(
                     InvalidBlock::SlotProcessingError(e),
                 ));
             }
         }
 
-        state.build_committee_cache(RelativeEpoch::Current, &T::EthSpec::spec())?;
+        state.build_committee_cache(RelativeEpoch::Current, &self.spec)?;
 
         // Apply the received block to its parent state (which has been transitioned into this
         // slot).
-        if let Err(e) = per_block_processing(&mut state, &block, &T::EthSpec::spec()) {
+        if let Err(e) = per_block_processing(&mut state, &block, &self.spec) {
             return Ok(BlockProcessingOutcome::InvalidBlock(
                 InvalidBlock::PerBlockProcessingError(e),
             ));
@@ -740,7 +738,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         // Register the new block with the fork choice service.
         self.fork_choice
             .write()
-            .add_block(&block, &block_root, &T::EthSpec::spec())?;
+            .add_block(&block, &block_root, &self.spec)?;
 
         // Execute the fork choice algorithm, enthroning a new head if discovered.
         //
@@ -771,7 +769,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
         let mut state = self.state.read().clone();
 
-        state.build_committee_cache(RelativeEpoch::Current, &T::EthSpec::spec())?;
+        state.build_committee_cache(RelativeEpoch::Current, &self.spec)?;
 
         trace!("Finding attestations for new block...");
 
@@ -783,9 +781,8 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             state.latest_block_header.canonical_root()
         };
 
-        let (proposer_slashings, attester_slashings) = self
-            .op_pool
-            .get_slashings(&*self.state.read(), &T::EthSpec::spec());
+        let (proposer_slashings, attester_slashings) =
+            self.op_pool.get_slashings(&*self.state.read(), &self.spec);
 
         let mut block = BeaconBlock {
             slot: state.slot,
@@ -806,16 +803,12 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 attester_slashings,
                 attestations: self
                     .op_pool
-                    .get_attestations(&*self.state.read(), &T::EthSpec::spec()),
-                deposits: self
-                    .op_pool
-                    .get_deposits(&*self.state.read(), &T::EthSpec::spec()),
+                    .get_attestations(&*self.state.read(), &self.spec),
+                deposits: self.op_pool.get_deposits(&*self.state.read(), &self.spec),
                 voluntary_exits: self
                     .op_pool
-                    .get_voluntary_exits(&*self.state.read(), &T::EthSpec::spec()),
-                transfers: self
-                    .op_pool
-                    .get_transfers(&*self.state.read(), &T::EthSpec::spec()),
+                    .get_voluntary_exits(&*self.state.read(), &self.spec),
+                transfers: self.op_pool.get_transfers(&*self.state.read(), &self.spec),
             },
         };
 
@@ -824,11 +817,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             block.body.attestations.len()
         );
 
-        per_block_processing_without_verifying_block_signature(
-            &mut state,
-            &block,
-            &T::EthSpec::spec(),
-        )?;
+        per_block_processing_without_verifying_block_signature(&mut state, &block, &self.spec)?;
 
         let state_root = state.canonical_root();
 
@@ -849,7 +838,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
         let justified_root = {
             let root = self.head().beacon_state.current_justified_root;
-            if root == T::EthSpec::spec().zero_hash {
+            if root == self.spec.zero_hash {
                 self.genesis_block_root
             } else {
                 root
@@ -860,7 +849,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         let beacon_block_root = self
             .fork_choice
             .write()
-            .find_head(&justified_root, &T::EthSpec::spec())?;
+            .find_head(&justified_root, &self.spec)?;
 
         // End fork choice metrics timer.
         timer.observe_duration();
@@ -920,7 +909,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         loop {
             let beacon_block_root = last_slot.beacon_block.previous_block_root;
 
-            if beacon_block_root == T::EthSpec::spec().zero_hash {
+            if beacon_block_root == self.spec.zero_hash {
                 break; // Genesis has been reached.
             }
 
diff --git a/beacon_node/beacon_chain/src/iter.rs b/beacon_node/beacon_chain/src/iter.rs
index 3147fb207..48caaf618 100644
--- a/beacon_node/beacon_chain/src/iter.rs
+++ b/beacon_node/beacon_chain/src/iter.rs
@@ -85,8 +85,11 @@ mod test {
     use types::{test_utils::TestingBeaconStateBuilder, FoundationEthSpec, Keypair};
 
     fn get_state<T: EthSpec>() -> BeaconState<T> {
-        let builder =
-            TestingBeaconStateBuilder::from_single_keypair(0, &Keypair::random(), &T::spec());
+        let builder = TestingBeaconStateBuilder::from_single_keypair(
+            0,
+            &Keypair::random(),
+            &T::default_spec(),
+        );
         let (state, _keypairs) = builder.build();
         state
     }
diff --git a/beacon_node/client/src/beacon_chain_types.rs b/beacon_node/client/src/beacon_chain_types.rs
index 37b1d261d..9747b1dd8 100644
--- a/beacon_node/client/src/beacon_chain_types.rs
+++ b/beacon_node/client/src/beacon_chain_types.rs
@@ -10,7 +10,8 @@ use slot_clock::SlotClock;
 use std::sync::Arc;
 use tree_hash::TreeHash;
 use types::{
-    test_utils::TestingBeaconStateBuilder, BeaconBlock, EthSpec, Hash256, LighthouseTestnetEthSpec,
+    test_utils::TestingBeaconStateBuilder, BeaconBlock, ChainSpec, EthSpec, Hash256,
+    LighthouseTestnetEthSpec,
 };
 
 /// The number initial validators when starting the `LighthouseTestnet`.
@@ -18,8 +19,12 @@ const TESTNET_VALIDATOR_COUNT: usize = 16;
 
 /// Provides a new, initialized `BeaconChain`
 pub trait InitialiseBeaconChain<T: BeaconChainTypes> {
-    fn initialise_beacon_chain(store: Arc<T::Store>, log: Logger) -> BeaconChain<T> {
-        maybe_load_from_store_for_testnet::<_, T::Store, T::EthSpec>(store, log)
+    fn initialise_beacon_chain(
+        store: Arc<T::Store>,
+        spec: ChainSpec,
+        log: Logger,
+    ) -> BeaconChain<T> {
+        maybe_load_from_store_for_testnet::<_, T::Store, T::EthSpec>(store, spec, log)
     }
 }
 
@@ -48,13 +53,14 @@ impl<T: BeaconChainTypes> InitialiseBeaconChain<T> for TestnetDiskBeaconChainTyp
 /// Loads a `BeaconChain` from `store`, if it exists. Otherwise, create a new chain from genesis.
 fn maybe_load_from_store_for_testnet<T, U: Store, V: EthSpec>(
     store: Arc<U>,
+    spec: ChainSpec,
     log: Logger,
 ) -> BeaconChain<T>
 where
     T: BeaconChainTypes<Store = U>,
     T::ForkChoice: ForkChoice<U>,
 {
-    if let Ok(Some(beacon_chain)) = BeaconChain::from_store(store.clone()) {
+    if let Ok(Some(beacon_chain)) = BeaconChain::from_store(store.clone(), spec.clone()) {
         info!(
             log,
             "Loaded BeaconChain from store";
@@ -65,8 +71,6 @@ where
         beacon_chain
     } else {
         info!(log, "Initializing new BeaconChain from genesis");
-        let spec = T::EthSpec::spec();
-
         let state_builder = TestingBeaconStateBuilder::from_default_keypairs_file_if_exists(
             TESTNET_VALIDATOR_COUNT,
             &spec,
@@ -92,7 +96,7 @@ where
             slot_clock,
             genesis_state,
             genesis_block,
-            spec.clone(),
+            spec,
             fork_choice,
         )
         .expect("Terminate if beacon chain generation fails")
diff --git a/beacon_node/client/src/client_config.rs b/beacon_node/client/src/client_config.rs
index baa9205ce..a729531ad 100644
--- a/beacon_node/client/src/client_config.rs
+++ b/beacon_node/client/src/client_config.rs
@@ -4,24 +4,26 @@ use network::NetworkConfig;
 use serde_derive::{Deserialize, Serialize};
 use std::fs;
 use std::path::PathBuf;
+use types::ChainSpec;
 
 /// The core configuration of a Lighthouse beacon node.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ClientConfig {
     pub data_dir: String,
-    pub spec: String,
+    pub spec_constants: String,
     pub db_type: String,
     db_name: String,
     pub network: network::NetworkConfig,
     pub rpc: rpc::RPCConfig,
     pub http: HttpServerConfig, //pub ipc_conf:
+    pub spec: ChainSpec,
 }
 
 impl Default for ClientConfig {
     fn default() -> Self {
         Self {
             data_dir: ".lighthouse".to_string(),
-            spec: "testnet".to_string(),
+            spec_constants: "testnet".to_string(),
             db_type: "disk".to_string(),
             db_name: "chain_db".to_string(),
             // Note: there are no default bootnodes specified.
@@ -29,6 +31,7 @@ impl Default for ClientConfig {
             network: NetworkConfig::new(vec![]),
             rpc: rpc::RPCConfig::default(),
             http: HttpServerConfig::default(),
+            spec: ChainSpec::lighthouse_testnet(8),
         }
     }
 }
diff --git a/beacon_node/client/src/lib.rs b/beacon_node/client/src/lib.rs
index 36d1c7d1f..ae28858c5 100644
--- a/beacon_node/client/src/lib.rs
+++ b/beacon_node/client/src/lib.rs
@@ -17,7 +17,6 @@ use std::sync::Arc;
 use std::time::{Duration, Instant};
 use tokio::runtime::TaskExecutor;
 use tokio::timer::Interval;
-use types::EthSpec;
 
 pub use beacon_chain::BeaconChainTypes;
 pub use beacon_chain_types::InitialiseBeaconChain;
@@ -58,10 +57,14 @@ where
     ) -> error::Result<Self> {
         let metrics_registry = Registry::new();
         let store = Arc::new(store);
-        let spec = T::EthSpec::spec();
+        let seconds_per_slot = config.spec.seconds_per_slot;
 
         // Load a `BeaconChain` from the store, or create a new one if it does not exist.
-        let beacon_chain = Arc::new(T::initialise_beacon_chain(store, log.clone()));
+        let beacon_chain = Arc::new(T::initialise_beacon_chain(
+            store,
+            config.spec.clone(),
+            log.clone(),
+        ));
         // Registry all beacon chain metrics with the global registry.
         beacon_chain
             .metrics
@@ -143,7 +146,7 @@ where
             // set up the validator work interval - start at next slot and proceed every slot
             let interval = {
                 // Set the interval to start at the next slot, and every slot after
-                let slot_duration = Duration::from_secs(spec.seconds_per_slot);
+                let slot_duration = Duration::from_secs(seconds_per_slot);
                 //TODO: Handle checked add correctly
                 Interval::new(Instant::now() + duration_to_next_slot, slot_duration)
             };
diff --git a/beacon_node/eth2-libp2p/src/behaviour.rs b/beacon_node/eth2-libp2p/src/behaviour.rs
index 8f3a000e1..476cddfbb 100644
--- a/beacon_node/eth2-libp2p/src/behaviour.rs
+++ b/beacon_node/eth2-libp2p/src/behaviour.rs
@@ -261,7 +261,7 @@ mod test {
 
     #[test]
     fn ssz_encoding() {
-        let original = PubsubMessage::Block(BeaconBlock::empty(&FoundationEthSpec::spec()));
+        let original = PubsubMessage::Block(BeaconBlock::empty(&FoundationEthSpec::default_spec()));
 
         let encoded = ssz_encode(&original);
 
diff --git a/beacon_node/http_server/src/api.rs b/beacon_node/http_server/src/api.rs
index 2594f9c28..a91080899 100644
--- a/beacon_node/http_server/src/api.rs
+++ b/beacon_node/http_server/src/api.rs
@@ -10,7 +10,6 @@ use persistent::Read;
 use router::Router;
 use serde_json::json;
 use std::sync::Arc;
-use types::EthSpec;
 
 /// Yields a handler for the HTTP API.
 pub fn build_handler<T: BeaconChainTypes + 'static>(
@@ -65,7 +64,7 @@ fn handle_fork<T: BeaconChainTypes + 'static>(req: &mut Request) -> IronResult<R
 
     let response = json!({
         "fork": beacon_chain.head().beacon_state.fork,
-        "chain_id": T::EthSpec::spec().chain_id
+        "chain_id": beacon_chain.spec.chain_id
     });
 
     Ok(Response::with((Status::Ok, response.to_string())))
diff --git a/beacon_node/network/src/sync/simple_sync.rs b/beacon_node/network/src/sync/simple_sync.rs
index c3fb03ca1..7f6421e32 100644
--- a/beacon_node/network/src/sync/simple_sync.rs
+++ b/beacon_node/network/src/sync/simple_sync.rs
@@ -158,7 +158,7 @@ impl<T: BeaconChainTypes> SimpleSync<T> {
         hello: HelloMessage,
         network: &mut NetworkContext,
     ) {
-        let spec = T::EthSpec::spec();
+        let spec = &self.chain.spec;
 
         let remote = PeerSyncInfo::from(hello);
         let local = PeerSyncInfo::from(&self.chain);
@@ -214,7 +214,7 @@ impl<T: BeaconChainTypes> SimpleSync<T> {
                 debug!(self.log, "Peer has high finalized epoch"; "peer" => format!("{:?}", peer_id));
                 let start_slot = local
                     .latest_finalized_epoch
-                    .start_slot(spec.slots_per_epoch);
+                    .start_slot(T::EthSpec::slots_per_epoch());
                 let required_slots = remote.best_slot - start_slot;
 
                 self.request_block_roots(
@@ -231,7 +231,7 @@ impl<T: BeaconChainTypes> SimpleSync<T> {
                 debug!(self.log, "Peer has higher best slot"; "peer" => format!("{:?}", peer_id));
                 let start_slot = local
                     .latest_finalized_epoch
-                    .start_slot(spec.slots_per_epoch);
+                    .start_slot(T::EthSpec::slots_per_epoch());
                 let required_slots = remote.best_slot - start_slot;
 
                 self.request_block_roots(
@@ -795,7 +795,7 @@ impl<T: BeaconChainTypes> SimpleSync<T> {
     fn slot_is_finalized(&self, slot: Slot) -> bool {
         slot <= hello_message(&self.chain)
             .latest_finalized_epoch
-            .start_slot(T::EthSpec::spec().slots_per_epoch)
+            .start_slot(T::EthSpec::slots_per_epoch())
     }
 
     /// Generates our current state in the form of a HELLO RPC message.
@@ -806,7 +806,7 @@ impl<T: BeaconChainTypes> SimpleSync<T> {
 
 /// Build a `HelloMessage` representing the state of the given `beacon_chain`.
 fn hello_message<T: BeaconChainTypes>(beacon_chain: &BeaconChain<T>) -> HelloMessage {
-    let spec = T::EthSpec::spec();
+    let spec = &beacon_chain.spec;
     let state = &beacon_chain.head().beacon_state;
 
     HelloMessage {
diff --git a/beacon_node/rpc/src/beacon_node.rs b/beacon_node/rpc/src/beacon_node.rs
index 8b49b193e..631601ac9 100644
--- a/beacon_node/rpc/src/beacon_node.rs
+++ b/beacon_node/rpc/src/beacon_node.rs
@@ -5,7 +5,6 @@ use protos::services::{Empty, Fork, NodeInfoResponse};
 use protos::services_grpc::BeaconNodeService;
 use slog::{trace, warn};
 use std::sync::Arc;
-use types::EthSpec;
 
 #[derive(Clone)]
 pub struct BeaconNodeServiceInstance<T: BeaconChainTypes> {
@@ -33,7 +32,7 @@ impl<T: BeaconChainTypes> BeaconNodeService for BeaconNodeServiceInstance<T> {
         fork.set_current_version(state_fork.current_version.to_vec());
         fork.set_epoch(state_fork.epoch.into());
 
-        let spec = T::EthSpec::spec();
+        let spec = &self.chain.spec;
 
         node_info.set_fork(fork);
         node_info.set_genesis_time(genesis_time);
diff --git a/beacon_node/rpc/src/validator.rs b/beacon_node/rpc/src/validator.rs
index 2cd374d25..b13303e25 100644
--- a/beacon_node/rpc/src/validator.rs
+++ b/beacon_node/rpc/src/validator.rs
@@ -14,7 +14,6 @@ pub struct ValidatorServiceInstance<T: BeaconChainTypes> {
     pub chain: Arc<BeaconChain<T>>,
     pub log: slog::Logger,
 }
-//TODO: Refactor Errors
 
 impl<T: BeaconChainTypes> ValidatorService for ValidatorServiceInstance<T> {
     /// For a list of validator public keys, this function returns the slot at which each
@@ -29,14 +28,15 @@ impl<T: BeaconChainTypes> ValidatorService for ValidatorServiceInstance<T> {
         let validators = req.get_validators();
         trace!(self.log, "RPC request"; "endpoint" => "GetValidatorDuties", "epoch" => req.get_epoch());
 
-        let spec = T::EthSpec::spec();
+        let spec = &self.chain.spec;
         let state = &self.chain.current_state();
         let epoch = Epoch::from(req.get_epoch());
         let mut resp = GetDutiesResponse::new();
         let resp_validators = resp.mut_active_validators();
 
         let relative_epoch =
-            match RelativeEpoch::from_epoch(state.slot.epoch(spec.slots_per_epoch), epoch) {
+            match RelativeEpoch::from_epoch(state.slot.epoch(T::EthSpec::slots_per_epoch()), epoch)
+            {
                 Ok(v) => v,
                 Err(e) => {
                     // incorrect epoch
@@ -52,7 +52,7 @@ impl<T: BeaconChainTypes> ValidatorService for ValidatorServiceInstance<T> {
             };
 
         let validator_proposers: Result<Vec<usize>, _> = epoch
-            .slot_iter(spec.slots_per_epoch)
+            .slot_iter(T::EthSpec::slots_per_epoch())
             .map(|slot| state.get_beacon_proposer_index(slot, relative_epoch, &spec))
             .collect();
         let validator_proposers = match validator_proposers {
@@ -148,7 +148,7 @@ impl<T: BeaconChainTypes> ValidatorService for ValidatorServiceInstance<T> {
             // check if the validator needs to propose a block
             if let Some(slot) = validator_proposers.iter().position(|&v| val_index == v) {
                 duty.set_block_production_slot(
-                    epoch.start_slot(spec.slots_per_epoch).as_u64() + slot as u64,
+                    epoch.start_slot(T::EthSpec::slots_per_epoch()).as_u64() + slot as u64,
                 );
             } else {
                 // no blocks to propose this epoch
diff --git a/beacon_node/src/run.rs b/beacon_node/src/run.rs
index f3d656ad3..0638e9ec9 100644
--- a/beacon_node/src/run.rs
+++ b/beacon_node/src/run.rs
@@ -27,11 +27,11 @@ pub fn run_beacon_node(config: ClientConfig, log: &slog::Logger) -> error::Resul
         .db_path()
         .ok_or_else::<error::Error, _>(|| "Unable to access database path".into())?;
     let db_type = &config.db_type;
-    let spec = &config.spec;
+    let spec_constants = &config.spec_constants;
 
     let other_config = config.clone();
 
-    let result = match (db_type.as_str(), spec.as_str()) {
+    let result = match (db_type.as_str(), spec_constants.as_str()) {
         ("disk", "testnet") => {
             run::<TestnetDiskBeaconChainTypes>(&db_path, config, executor, runtime, log)
         }
@@ -50,7 +50,7 @@ pub fn run_beacon_node(config: ClientConfig, log: &slog::Logger) -> error::Resul
             "Started beacon node";
             "p2p_listen_addresses" => format!("{:?}", &other_config.network.listen_addresses()),
             "data_dir" => format!("{:?}", other_config.data_dir()),
-            "spec" => &other_config.spec,
+            "spec_constants" => &other_config.spec_constants,
             "db_type" => &other_config.db_type,
         );
     }
diff --git a/beacon_node/store/src/block_at_slot.rs b/beacon_node/store/src/block_at_slot.rs
index 260a35114..b7346e90d 100644
--- a/beacon_node/store/src/block_at_slot.rs
+++ b/beacon_node/store/src/block_at_slot.rs
@@ -61,7 +61,7 @@ mod tests {
 
     #[test]
     fn read_slot() {
-        let spec = FewValidatorsEthSpec::spec();
+        let spec = FewValidatorsEthSpec::default_spec();
 
         let test_slot = |slot: Slot| {
             let mut block = BeaconBlock::empty(&spec);
@@ -85,7 +85,7 @@ mod tests {
 
     #[test]
     fn read_previous_block_root() {
-        let spec = FewValidatorsEthSpec::spec();
+        let spec = FewValidatorsEthSpec::default_spec();
 
         let test_root = |root: Hash256| {
             let mut block = BeaconBlock::empty(&spec);
@@ -130,7 +130,7 @@ mod tests {
     fn chain_without_skips() {
         let n: usize = 10;
         let store = MemoryStore::open();
-        let spec = FewValidatorsEthSpec::spec();
+        let spec = FewValidatorsEthSpec::default_spec();
 
         let slots: Vec<usize> = (0..n).collect();
         let blocks_and_roots = build_chain(&store, &slots, &spec);
@@ -154,7 +154,7 @@ mod tests {
     #[test]
     fn chain_with_skips() {
         let store = MemoryStore::open();
-        let spec = FewValidatorsEthSpec::spec();
+        let spec = FewValidatorsEthSpec::default_spec();
 
         let slots = vec![0, 1, 2, 5];
 
diff --git a/eth2/fork_choice/benches/benches.rs b/eth2/fork_choice/benches/benches.rs
index 065cde655..b0495a80c 100644
--- a/eth2/fork_choice/benches/benches.rs
+++ b/eth2/fork_choice/benches/benches.rs
@@ -19,7 +19,7 @@ fn setup(
     let store = MemoryStore::open();
     let builder: TestingForkChoiceBuilder<MemoryStore, TestedEthSpec> =
         TestingForkChoiceBuilder::new(validator_count, chain_length, Arc::new(store));
-    let spec = TestedEthSpec::spec();
+    let spec = TestedEthSpec::default_spec();
 
     (builder, spec)
 }
diff --git a/eth2/fork_choice/examples/example.rs b/eth2/fork_choice/examples/example.rs
index 927cf23b7..7e42ad144 100644
--- a/eth2/fork_choice/examples/example.rs
+++ b/eth2/fork_choice/examples/example.rs
@@ -17,7 +17,7 @@ fn main() {
         .map(|_| builder.build())
         .collect();
 
-    let spec = &FoundationEthSpec::spec();
+    let spec = &FoundationEthSpec::default_spec();
 
     println!("Running {} times...", repetitions);
     for fc in fork_choosers {
diff --git a/eth2/fork_choice/src/bitwise_lmd_ghost.rs b/eth2/fork_choice/src/bitwise_lmd_ghost.rs
index f78a8e780..3ed57bf4d 100644
--- a/eth2/fork_choice/src/bitwise_lmd_ghost.rs
+++ b/eth2/fork_choice/src/bitwise_lmd_ghost.rs
@@ -68,7 +68,7 @@ impl<T: Store, E: EthSpec> BitwiseLMDGhost<T, E> {
             .ok_or_else(|| ForkChoiceError::MissingBeaconState(*state_root))?;
 
         let active_validator_indices =
-            current_state.get_active_validator_indices(block_slot.epoch(spec.slots_per_epoch));
+            current_state.get_active_validator_indices(block_slot.epoch(E::slots_per_epoch()));
 
         for index in active_validator_indices {
             let balance = std::cmp::min(current_state.balances[index], spec.max_effective_balance)
diff --git a/eth2/fork_choice/src/optimized_lmd_ghost.rs b/eth2/fork_choice/src/optimized_lmd_ghost.rs
index b389d0981..7a48c461e 100644
--- a/eth2/fork_choice/src/optimized_lmd_ghost.rs
+++ b/eth2/fork_choice/src/optimized_lmd_ghost.rs
@@ -68,7 +68,7 @@ impl<T: Store, E: EthSpec> OptimizedLMDGhost<T, E> {
             .ok_or_else(|| ForkChoiceError::MissingBeaconState(*state_root))?;
 
         let active_validator_indices =
-            current_state.get_active_validator_indices(block_slot.epoch(spec.slots_per_epoch));
+            current_state.get_active_validator_indices(block_slot.epoch(E::slots_per_epoch()));
 
         for index in active_validator_indices {
             let balance = std::cmp::min(current_state.balances[index], spec.max_effective_balance)
diff --git a/eth2/fork_choice/src/slow_lmd_ghost.rs b/eth2/fork_choice/src/slow_lmd_ghost.rs
index 7b5114887..9b7a20400 100644
--- a/eth2/fork_choice/src/slow_lmd_ghost.rs
+++ b/eth2/fork_choice/src/slow_lmd_ghost.rs
@@ -40,7 +40,7 @@ impl<T: Store, E: EthSpec> SlowLMDGhost<T, E> {
             .ok_or_else(|| ForkChoiceError::MissingBeaconState(*state_root))?;
 
         let active_validator_indices =
-            current_state.get_active_validator_indices(block_slot.epoch(spec.slots_per_epoch));
+            current_state.get_active_validator_indices(block_slot.epoch(E::slots_per_epoch()));
 
         for index in active_validator_indices {
             let balance = std::cmp::min(current_state.balances[index], spec.max_effective_balance)
diff --git a/eth2/fork_choice/src/test_utils.rs b/eth2/fork_choice/src/test_utils.rs
index 76264fcb6..c3bf39930 100644
--- a/eth2/fork_choice/src/test_utils.rs
+++ b/eth2/fork_choice/src/test_utils.rs
@@ -40,10 +40,10 @@ impl<S: Store, E: EthSpec> TestingForkChoiceBuilder<S, E> {
 }
 
 fn get_state<T: EthSpec>(validator_count: usize) -> BeaconState<T> {
-    let spec = &T::spec();
+    let spec = T::default_spec();
 
     let builder: TestingBeaconStateBuilder<T> =
-        TestingBeaconStateBuilder::from_single_keypair(validator_count, &Keypair::random(), spec);
+        TestingBeaconStateBuilder::from_single_keypair(validator_count, &Keypair::random(), &spec);
     let (state, _keypairs) = builder.build();
     state
 }
@@ -58,7 +58,7 @@ fn get_chain_of_blocks<T: EthSpec, U: Store>(
     validator_count: usize,
     store: Arc<U>,
 ) -> Vec<(Hash256, BeaconBlock)> {
-    let spec = T::spec();
+    let spec = T::default_spec();
     let mut blocks_and_roots: Vec<(Hash256, BeaconBlock)> = vec![];
     let mut unique_hashes = (0..).into_iter().map(|i| Hash256::from(i));
     let mut random_block = BeaconBlock::random_for_test(&mut XorShiftRng::from_seed([42; 16]));
diff --git a/eth2/fork_choice/tests/tests.rs b/eth2/fork_choice/tests/tests.rs
index 9270571ca..59e4e0ee0 100644
--- a/eth2/fork_choice/tests/tests.rs
+++ b/eth2/fork_choice/tests/tests.rs
@@ -61,7 +61,7 @@ fn test_yaml_vectors<T: ForkChoice<MemoryStore>>(
     let test_cases = load_test_cases_from_yaml(yaml_file_path);
 
     // default vars
-    let spec = FoundationEthSpec::spec();
+    let spec = FoundationEthSpec::default_spec();
     let zero_hash = Hash256::zero();
     let eth1_data = Eth1Data {
         deposit_count: 0,
@@ -204,7 +204,7 @@ where
     let store = Arc::new(MemoryStore::open());
 
     let fork_choice = ForkChoice::new(store.clone());
-    let spec = FoundationEthSpec::spec();
+    let spec = FoundationEthSpec::default_spec();
 
     let mut state_builder: TestingBeaconStateBuilder<FoundationEthSpec> =
         TestingBeaconStateBuilder::from_single_keypair(num_validators, &Keypair::random(), &spec);
diff --git a/eth2/operation_pool/src/lib.rs b/eth2/operation_pool/src/lib.rs
index 0affba3f4..0cd46e018 100644
--- a/eth2/operation_pool/src/lib.rs
+++ b/eth2/operation_pool/src/lib.rs
@@ -676,7 +676,7 @@ mod tests {
     }
 
     fn test_state(rng: &mut XorShiftRng) -> (ChainSpec, BeaconState<FoundationEthSpec>) {
-        let spec = FoundationEthSpec::spec();
+        let spec = FoundationEthSpec::default_spec();
 
         let mut state = BeaconState::random_for_test(rng);
 
@@ -721,21 +721,21 @@ mod tests {
         fn attestation_test_state<E: EthSpec>(
             num_committees: usize,
         ) -> (BeaconState<E>, Vec<Keypair>, ChainSpec) {
-            let spec = E::spec();
+            let spec = E::default_spec();
 
             let num_validators =
-                num_committees * spec.slots_per_epoch as usize * spec.target_committee_size;
+                num_committees * T::slots_per_epoch() as usize * spec.target_committee_size;
             let mut state_builder = TestingBeaconStateBuilder::from_default_keypairs_file_if_exists(
                 num_validators,
                 &spec,
             );
-            let slot_offset = 1000 * spec.slots_per_epoch + spec.slots_per_epoch / 2;
+            let slot_offset = 1000 * T::slots_per_epoch() + T::slots_per_epoch() / 2;
             let slot = spec.genesis_slot + slot_offset;
             state_builder.teleport_to_slot(slot, &spec);
             state_builder.build_caches(&spec).unwrap();
             let (state, keypairs) = state_builder.build();
 
-            (state, keypairs, FoundationEthSpec::spec())
+            (state, keypairs, FoundationEthSpec::default_spec())
         }
 
         #[test]
@@ -852,7 +852,7 @@ mod tests {
 
             // But once we advance to more than an epoch after the attestation, it should prune it
             // out of existence.
-            state.slot += 2 * spec.slots_per_epoch;
+            state.slot += 2 * T::slots_per_epoch();
             op_pool.prune_attestations(state);
             assert_eq!(op_pool.num_attestations(), 0);
         }
diff --git a/eth2/state_processing/benches/bench_epoch_processing.rs b/eth2/state_processing/benches/bench_epoch_processing.rs
index 9bff3a2e3..23e662e09 100644
--- a/eth2/state_processing/benches/bench_epoch_processing.rs
+++ b/eth2/state_processing/benches/bench_epoch_processing.rs
@@ -23,7 +23,7 @@ pub fn bench_epoch_processing_n_validators(c: &mut Criterion, validator_count: u
         TestingBeaconStateBuilder::from_default_keypairs_file_if_exists(validator_count, &spec);
 
     // Set the state to be just before an epoch transition.
-    let target_slot = (spec.genesis_epoch + 4).end_slot(spec.slots_per_epoch);
+    let target_slot = (spec.genesis_epoch + 4).end_slot(T::slots_per_epoch());
     builder.teleport_to_slot(target_slot, &spec);
 
     // Builds all caches; benches will not contain shuffling/committee building times.
@@ -38,10 +38,10 @@ pub fn bench_epoch_processing_n_validators(c: &mut Criterion, validator_count: u
     // Assert that the state has an attestations for each committee that is able to include an
     // attestation in the state.
     let committees_per_epoch = spec.get_epoch_committee_count(validator_count);
-    let committees_per_slot = committees_per_epoch / spec.slots_per_epoch;
+    let committees_per_slot = committees_per_epoch / T::slots_per_epoch();
     let previous_epoch_attestations = committees_per_epoch;
     let current_epoch_attestations =
-        committees_per_slot * (spec.slots_per_epoch - spec.min_attestation_inclusion_delay);
+        committees_per_slot * (T::slots_per_epoch() - spec.min_attestation_inclusion_delay);
     assert_eq!(
         state.latest_attestations.len() as u64,
         previous_epoch_attestations + current_epoch_attestations,
diff --git a/eth2/state_processing/benches/benches.rs b/eth2/state_processing/benches/benches.rs
index 0cf797147..1a153abee 100644
--- a/eth2/state_processing/benches/benches.rs
+++ b/eth2/state_processing/benches/benches.rs
@@ -34,7 +34,7 @@ pub fn block_processing_worst_case(c: &mut Criterion) {
     bench_builder.maximize_block_operations(&spec);
 
     // Set the state and block to be in the last slot of the 4th epoch.
-    let last_slot_of_epoch = (spec.genesis_epoch + 4).end_slot(spec.slots_per_epoch);
+    let last_slot_of_epoch = (spec.genesis_epoch + 4).end_slot(T::slots_per_epoch());
     bench_builder.set_slot(last_slot_of_epoch, &spec);
 
     // Build all the state caches so the build times aren't included in the benches.
@@ -67,13 +67,13 @@ pub fn block_processing_reasonable_case(c: &mut Criterion) {
     // Set the number of included operations to what we might expect normally.
     bench_builder.num_proposer_slashings = 0;
     bench_builder.num_attester_slashings = 0;
-    bench_builder.num_attestations = (spec.shard_count / spec.slots_per_epoch) as usize;
+    bench_builder.num_attestations = (spec.shard_count / T::slots_per_epoch()) as usize;
     bench_builder.num_deposits = 2;
     bench_builder.num_exits = 2;
     bench_builder.num_transfers = 2;
 
     // Set the state and block to be in the last slot of the 4th epoch.
-    let last_slot_of_epoch = (spec.genesis_epoch + 4).end_slot(spec.slots_per_epoch);
+    let last_slot_of_epoch = (spec.genesis_epoch + 4).end_slot(T::slots_per_epoch());
     bench_builder.set_slot(last_slot_of_epoch, &spec);
 
     // Build all the state caches so the build times aren't included in the benches.
diff --git a/eth2/state_processing/src/per_block_processing.rs b/eth2/state_processing/src/per_block_processing.rs
index 56238f9c2..437cd459c 100644
--- a/eth2/state_processing/src/per_block_processing.rs
+++ b/eth2/state_processing/src/per_block_processing.rs
@@ -140,7 +140,7 @@ pub fn verify_block_signature<T: EthSpec>(
         [state.get_beacon_proposer_index(block.slot, RelativeEpoch::Current, spec)?];
 
     let domain = spec.get_domain(
-        block.slot.epoch(spec.slots_per_epoch),
+        block.slot.epoch(T::slots_per_epoch()),
         Domain::BeaconProposer,
         &state.fork,
     );
@@ -172,7 +172,7 @@ pub fn process_randao<T: EthSpec>(
         block.body.randao_reveal.verify(
             &state.current_epoch().tree_hash_root()[..],
             spec.get_domain(
-                block.slot.epoch(spec.slots_per_epoch),
+                block.slot.epoch(T::slots_per_epoch()),
                 Domain::Randao,
                 &state.fork
             ),
diff --git a/eth2/state_processing/src/per_block_processing/block_processing_builder.rs b/eth2/state_processing/src/per_block_processing/block_processing_builder.rs
index 35e736d5f..5a9d264ce 100644
--- a/eth2/state_processing/src/per_block_processing/block_processing_builder.rs
+++ b/eth2/state_processing/src/per_block_processing/block_processing_builder.rs
@@ -55,11 +55,13 @@ impl<T: EthSpec> BlockProcessingBuilder<T> {
         let keypair = &keypairs[proposer_index];
 
         match randao_sk {
-            Some(sk) => builder.set_randao_reveal(&sk, &state.fork, spec),
-            None => builder.set_randao_reveal(&keypair.sk, &state.fork, spec),
+            Some(sk) => builder.set_randao_reveal::<T>(&sk, &state.fork, spec),
+            None => builder.set_randao_reveal::<T>(&keypair.sk, &state.fork, spec),
         }
 
-        let block = self.block_builder.build(&keypair.sk, &state.fork, spec);
+        let block = self
+            .block_builder
+            .build::<T>(&keypair.sk, &state.fork, spec);
 
         (block, state)
     }
diff --git a/eth2/state_processing/src/per_block_processing/tests.rs b/eth2/state_processing/src/per_block_processing/tests.rs
index 28ed9c4f0..fe30560c6 100644
--- a/eth2/state_processing/src/per_block_processing/tests.rs
+++ b/eth2/state_processing/src/per_block_processing/tests.rs
@@ -9,7 +9,7 @@ pub const VALIDATOR_COUNT: usize = 10;
 
 #[test]
 fn valid_block_ok() {
-    let spec = FoundationEthSpec::spec();
+    let spec = FoundationEthSpec::default_spec();
     let builder = get_builder(&spec);
     let (block, mut state) = builder.build(None, None, &spec);
 
@@ -20,7 +20,7 @@ fn valid_block_ok() {
 
 #[test]
 fn invalid_block_header_state_slot() {
-    let spec = FoundationEthSpec::spec();
+    let spec = FoundationEthSpec::default_spec();
     let builder = get_builder(&spec);
     let (mut block, mut state) = builder.build(None, None, &spec);
 
@@ -39,7 +39,7 @@ fn invalid_block_header_state_slot() {
 
 #[test]
 fn invalid_parent_block_root() {
-    let spec = FoundationEthSpec::spec();
+    let spec = FoundationEthSpec::default_spec();
     let builder = get_builder(&spec);
     let invalid_parent_root = Hash256::from([0xAA; 32]);
     let (block, mut state) = builder.build(None, Some(invalid_parent_root), &spec);
@@ -59,14 +59,14 @@ fn invalid_parent_block_root() {
 
 #[test]
 fn invalid_block_signature() {
-    let spec = FoundationEthSpec::spec();
+    let spec = FoundationEthSpec::default_spec();
     let builder = get_builder(&spec);
     let (mut block, mut state) = builder.build(None, None, &spec);
 
     // sign the block with a keypair that is not the expected proposer
     let keypair = Keypair::random();
     let message = block.signed_root();
-    let epoch = block.slot.epoch(spec.slots_per_epoch);
+    let epoch = block.slot.epoch(FoundationEthSpec::slots_per_epoch());
     let domain = spec.get_domain(epoch, Domain::BeaconProposer, &state.fork);
     block.signature = Signature::new(&message, domain, &keypair.sk);
 
@@ -82,7 +82,7 @@ fn invalid_block_signature() {
 
 #[test]
 fn invalid_randao_reveal_signature() {
-    let spec = FoundationEthSpec::spec();
+    let spec = FoundationEthSpec::default_spec();
     let builder = get_builder(&spec);
 
     // sign randao reveal with random keypair
@@ -104,7 +104,8 @@ fn get_builder(spec: &ChainSpec) -> (BlockProcessingBuilder<FoundationEthSpec>)
     let mut builder = BlockProcessingBuilder::new(VALIDATOR_COUNT, &spec);
 
     // Set the state and block to be in the last slot of the 4th epoch.
-    let last_slot_of_epoch = (spec.genesis_epoch + 4).end_slot(spec.slots_per_epoch);
+    let last_slot_of_epoch =
+        (spec.genesis_epoch + 4).end_slot(FoundationEthSpec::slots_per_epoch());
     builder.set_slot(last_slot_of_epoch, &spec);
     builder.build_caches(&spec);
 
diff --git a/eth2/state_processing/src/per_block_processing/validate_attestation.rs b/eth2/state_processing/src/per_block_processing/validate_attestation.rs
index 1058c0d21..379b921f4 100644
--- a/eth2/state_processing/src/per_block_processing/validate_attestation.rs
+++ b/eth2/state_processing/src/per_block_processing/validate_attestation.rs
@@ -68,7 +68,7 @@ fn validate_attestation_parametric<T: EthSpec>(
         }
     );
     verify!(
-        state.slot <= attestation_slot + spec.slots_per_epoch,
+        state.slot <= attestation_slot + T::slots_per_epoch(),
         Invalid::IncludedTooLate {
             state: state.slot,
             attestation: attestation_slot
diff --git a/eth2/state_processing/src/per_block_processing/verify_proposer_slashing.rs b/eth2/state_processing/src/per_block_processing/verify_proposer_slashing.rs
index 98a9a248c..744427ad9 100644
--- a/eth2/state_processing/src/per_block_processing/verify_proposer_slashing.rs
+++ b/eth2/state_processing/src/per_block_processing/verify_proposer_slashing.rs
@@ -21,8 +21,8 @@ pub fn verify_proposer_slashing<T: EthSpec>(
         })?;
 
     verify!(
-        proposer_slashing.header_1.slot.epoch(spec.slots_per_epoch)
-            == proposer_slashing.header_2.slot.epoch(spec.slots_per_epoch),
+        proposer_slashing.header_1.slot.epoch(T::slots_per_epoch())
+            == proposer_slashing.header_2.slot.epoch(T::slots_per_epoch()),
         Invalid::ProposalEpochMismatch(
             proposer_slashing.header_1.slot,
             proposer_slashing.header_2.slot
@@ -40,7 +40,7 @@ pub fn verify_proposer_slashing<T: EthSpec>(
     );
 
     verify!(
-        verify_header_signature(
+        verify_header_signature::<T>(
             &proposer_slashing.header_1,
             &proposer.pubkey,
             &state.fork,
@@ -49,7 +49,7 @@ pub fn verify_proposer_slashing<T: EthSpec>(
         Invalid::BadProposal1Signature
     );
     verify!(
-        verify_header_signature(
+        verify_header_signature::<T>(
             &proposer_slashing.header_2,
             &proposer.pubkey,
             &state.fork,
@@ -66,7 +66,7 @@ pub fn verify_proposer_slashing<T: EthSpec>(
 /// Returns `true` if the signature is valid.
 ///
 /// Spec v0.6.1
-fn verify_header_signature(
+fn verify_header_signature<T: EthSpec>(
     header: &BeaconBlockHeader,
     pubkey: &PublicKey,
     fork: &Fork,
@@ -74,7 +74,7 @@ fn verify_header_signature(
 ) -> bool {
     let message = header.signed_root();
     let domain = spec.get_domain(
-        header.slot.epoch(spec.slots_per_epoch),
+        header.slot.epoch(T::slots_per_epoch()),
         Domain::BeaconProposer,
         fork,
     );
diff --git a/eth2/state_processing/src/per_block_processing/verify_transfer.rs b/eth2/state_processing/src/per_block_processing/verify_transfer.rs
index 15c142d90..de4cef44f 100644
--- a/eth2/state_processing/src/per_block_processing/verify_transfer.rs
+++ b/eth2/state_processing/src/per_block_processing/verify_transfer.rs
@@ -101,7 +101,7 @@ fn verify_transfer_parametric<T: EthSpec>(
         .get(transfer.sender as usize)
         .ok_or_else(|| Error::Invalid(Invalid::FromValidatorUnknown(transfer.sender)))?;
 
-    let epoch = state.slot.epoch(spec.slots_per_epoch);
+    let epoch = state.slot.epoch(T::slots_per_epoch());
 
     // Ensure one of the following is met:
     //
@@ -136,7 +136,7 @@ fn verify_transfer_parametric<T: EthSpec>(
     // Verify the transfer signature.
     let message = transfer.signed_root();
     let domain = spec.get_domain(
-        transfer.slot.epoch(spec.slots_per_epoch),
+        transfer.slot.epoch(T::slots_per_epoch()),
         Domain::Transfer,
         &state.fork,
     );
diff --git a/eth2/state_processing/src/per_epoch_processing.rs b/eth2/state_processing/src/per_epoch_processing.rs
index d261b8b47..290c33804 100644
--- a/eth2/state_processing/src/per_epoch_processing.rs
+++ b/eth2/state_processing/src/per_epoch_processing.rs
@@ -237,7 +237,7 @@ pub fn process_final_updates<T: EthSpec>(
         state.slot -= 1;
     }
 
-    if next_epoch.as_u64() % (T::SlotsPerHistoricalRoot::to_u64() / spec.slots_per_epoch) == 0 {
+    if next_epoch.as_u64() % (T::SlotsPerHistoricalRoot::to_u64() / T::slots_per_epoch()) == 0 {
         let historical_batch = state.historical_batch();
         state
             .historical_roots
diff --git a/eth2/state_processing/src/per_epoch_processing/tests.rs b/eth2/state_processing/src/per_epoch_processing/tests.rs
index 9841a5551..0e5a81cce 100644
--- a/eth2/state_processing/src/per_epoch_processing/tests.rs
+++ b/eth2/state_processing/src/per_epoch_processing/tests.rs
@@ -8,12 +8,12 @@ use types::*;
 fn runs_without_error() {
     Builder::from_env(Env::default().default_filter_or("error")).init();
 
-    let spec = FewValidatorsEthSpec::spec();
+    let spec = FewValidatorsEthSpec::default_spec();
 
     let mut builder: TestingBeaconStateBuilder<FewValidatorsEthSpec> =
         TestingBeaconStateBuilder::from_deterministic_keypairs(8, &spec);
 
-    let target_slot = (spec.genesis_epoch + 4).end_slot(spec.slots_per_epoch);
+    let target_slot = (spec.genesis_epoch + 4).end_slot(FewValidatorsEthSpec::slots_per_epoch());
     builder.teleport_to_slot(target_slot, &spec);
 
     let (mut state, _keypairs) = builder.build();
diff --git a/eth2/state_processing/src/per_epoch_processing/validator_statuses.rs b/eth2/state_processing/src/per_epoch_processing/validator_statuses.rs
index ed1b968d7..76a485ea7 100644
--- a/eth2/state_processing/src/per_epoch_processing/validator_statuses.rs
+++ b/eth2/state_processing/src/per_epoch_processing/validator_statuses.rs
@@ -233,7 +233,7 @@ impl ValidatorStatuses {
                 let attestation_slot = state.get_attestation_slot(&a.data)?;
                 let inclusion_slot = attestation_slot + a.inclusion_delay;
                 let relative_epoch =
-                    RelativeEpoch::from_slot(state.slot, inclusion_slot, spec.slots_per_epoch)?;
+                    RelativeEpoch::from_slot(state.slot, inclusion_slot, T::slots_per_epoch())?;
                 status.inclusion_info = Some(InclusionInfo {
                     slot: inclusion_slot,
                     distance: a.inclusion_delay,
@@ -297,7 +297,7 @@ impl ValidatorStatuses {
         spec: &ChainSpec,
     ) -> Result<(), BeaconStateError> {
         // Loop through each slot in the previous epoch.
-        for slot in state.previous_epoch().slot_iter(spec.slots_per_epoch) {
+        for slot in state.previous_epoch().slot_iter(T::slots_per_epoch()) {
             let crosslink_committees_at_slot = state.get_crosslink_committees_at_slot(slot)?;
 
             // Loop through each committee in the slot.
@@ -338,7 +338,7 @@ fn target_matches_epoch_start_block<T: EthSpec>(
     epoch: Epoch,
     spec: &ChainSpec,
 ) -> Result<bool, BeaconStateError> {
-    let slot = epoch.start_slot(spec.slots_per_epoch);
+    let slot = epoch.start_slot(T::slots_per_epoch());
     let state_boundary_root = *state.get_block_root(slot)?;
 
     Ok(a.data.target_root == state_boundary_root)
diff --git a/eth2/state_processing/src/per_slot_processing.rs b/eth2/state_processing/src/per_slot_processing.rs
index 0fc074262..8adfe988b 100644
--- a/eth2/state_processing/src/per_slot_processing.rs
+++ b/eth2/state_processing/src/per_slot_processing.rs
@@ -16,7 +16,7 @@ pub fn per_slot_processing<T: EthSpec>(
 ) -> Result<(), Error> {
     cache_state(state, spec)?;
 
-    if (state.slot > spec.genesis_slot) && ((state.slot + 1) % spec.slots_per_epoch == 0) {
+    if (state.slot > spec.genesis_slot) && ((state.slot + 1) % T::slots_per_epoch() == 0) {
         per_epoch_processing(state, spec)?;
     }
 
diff --git a/eth2/types/src/beacon_state.rs b/eth2/types/src/beacon_state.rs
index b93738328..27a2e7a0e 100644
--- a/eth2/types/src/beacon_state.rs
+++ b/eth2/types/src/beacon_state.rs
@@ -458,7 +458,7 @@ impl<T: EthSpec> BeaconState<T> {
         epoch: Epoch,
         spec: &ChainSpec,
     ) -> Result<&Hash256, BeaconStateError> {
-        self.get_block_root(epoch.start_slot(spec.slots_per_epoch))
+        self.get_block_root(epoch.start_slot(T::slots_per_epoch()))
     }
 
     /// Sets the block root for some given slot.
diff --git a/eth2/types/src/beacon_state/beacon_state_types.rs b/eth2/types/src/beacon_state/beacon_state_types.rs
index ec6eb68bc..fce0c6dff 100644
--- a/eth2/types/src/beacon_state/beacon_state_types.rs
+++ b/eth2/types/src/beacon_state/beacon_state_types.rs
@@ -1,5 +1,5 @@
 use crate::*;
-use fixed_len_vec::typenum::{Unsigned, U1024, U8, U8192};
+use fixed_len_vec::typenum::{Unsigned, U0, U1024, U64, U8, U8192};
 use serde_derive::{Deserialize, Serialize};
 use std::fmt::Debug;
 
@@ -9,14 +9,24 @@ pub trait EthSpec: 'static + Default + Sync + Send + Clone + Debug + PartialEq {
     type LatestRandaoMixesLength: Unsigned + Clone + Sync + Send + Debug + PartialEq;
     type LatestActiveIndexRootsLength: Unsigned + Clone + Sync + Send + Debug + PartialEq;
     type LatestSlashedExitLength: Unsigned + Clone + Sync + Send + Debug + PartialEq;
+    /// Note: `SlotsPerEpoch` is not necessarily required to be a compile-time constant. We include
+    /// it here just for the convenience of not passing `slots_per_epoch` around all the time.
+    type SlotsPerEpoch: Unsigned + Clone + Sync + Send + Debug + PartialEq;
+    type GenesisEpoch: Unsigned + Clone + Sync + Send + Debug + PartialEq;
 
-    fn spec() -> ChainSpec;
+    fn default_spec() -> ChainSpec;
+
+    fn genesis_epoch() -> Epoch {
+        Epoch::new(Self::GenesisEpoch::to_u64())
+    }
 
     /// Return the number of committees in one epoch.
     ///
     /// Spec v0.6.1
-    fn get_epoch_committee_count(active_validator_count: usize) -> usize {
-        let target_committee_size = Self::spec().target_committee_size;
+    fn get_epoch_committee_count(
+        active_validator_count: usize,
+        target_committee_size: usize,
+    ) -> usize {
         let shard_count = Self::shard_count();
         let slots_per_epoch = Self::slots_per_epoch() as usize;
 
@@ -35,21 +45,14 @@ pub trait EthSpec: 'static + Default + Sync + Send + Clone + Debug + PartialEq {
     /// basic sense. This count is not required to provide any security guarantees regarding
     /// decentralization, entropy, etc.
     fn minimum_validator_count() -> usize {
-        Self::slots_per_epoch() as usize
+        Self::SlotsPerEpoch::to_usize()
     }
 
     /// Returns the `SLOTS_PER_EPOCH` constant for this specification.
     ///
     /// Spec v0.6.1
     fn slots_per_epoch() -> u64 {
-        Self::spec().slots_per_epoch
-    }
-
-    /// Returns the `SLOTS_PER_EPOCH` constant for this specification.
-    ///
-    /// Spec v0.6.1
-    fn genesis_epoch() -> Epoch {
-        Self::spec().genesis_epoch
+        Self::SlotsPerEpoch::to_u64()
     }
 
     /// Returns the `SHARD_COUNT` constant for this specification.
@@ -100,8 +103,10 @@ impl EthSpec for FoundationEthSpec {
     type LatestRandaoMixesLength = U8192;
     type LatestActiveIndexRootsLength = U8192;
     type LatestSlashedExitLength = U8192;
+    type SlotsPerEpoch = U64;
+    type GenesisEpoch = U0;
 
-    fn spec() -> ChainSpec {
+    fn default_spec() -> ChainSpec {
         ChainSpec::foundation()
     }
 }
@@ -118,9 +123,11 @@ impl EthSpec for FewValidatorsEthSpec {
     type LatestRandaoMixesLength = U8192;
     type LatestActiveIndexRootsLength = U8192;
     type LatestSlashedExitLength = U8192;
+    type SlotsPerEpoch = U8;
+    type GenesisEpoch = U0;
 
-    fn spec() -> ChainSpec {
-        ChainSpec::few_validators()
+    fn default_spec() -> ChainSpec {
+        ChainSpec::few_validators(Self::slots_per_epoch())
     }
 }
 
@@ -136,9 +143,11 @@ impl EthSpec for LighthouseTestnetEthSpec {
     type LatestRandaoMixesLength = U8192;
     type LatestActiveIndexRootsLength = U8192;
     type LatestSlashedExitLength = U8192;
+    type SlotsPerEpoch = U8;
+    type GenesisEpoch = U0;
 
-    fn spec() -> ChainSpec {
-        ChainSpec::lighthouse_testnet()
+    fn default_spec() -> ChainSpec {
+        ChainSpec::lighthouse_testnet(Self::slots_per_epoch())
     }
 }
 
diff --git a/eth2/types/src/beacon_state/committee_cache.rs b/eth2/types/src/beacon_state/committee_cache.rs
index d1e0e7030..78af72754 100644
--- a/eth2/types/src/beacon_state/committee_cache.rs
+++ b/eth2/types/src/beacon_state/committee_cache.rs
@@ -45,13 +45,18 @@ impl CommitteeCache {
             return Err(Error::InsufficientValidators);
         }
 
-        let committee_count = T::get_epoch_committee_count(active_validator_indices.len()) as usize;
+        let committee_count = T::get_epoch_committee_count(
+            active_validator_indices.len(),
+            spec.target_committee_size,
+        ) as usize;
 
         let shuffling_start_shard = match relative_epoch {
             RelativeEpoch::Current => state.latest_start_shard,
             RelativeEpoch::Previous => {
-                let committees_in_previous_epoch =
-                    T::get_epoch_committee_count(active_validator_indices.len()) as u64;
+                let committees_in_previous_epoch = T::get_epoch_committee_count(
+                    active_validator_indices.len(),
+                    spec.target_committee_size,
+                ) as u64;
 
                 (state.latest_start_shard + T::shard_count() as u64 - committees_in_previous_epoch)
                     % T::shard_count() as u64
@@ -59,8 +64,10 @@ impl CommitteeCache {
             RelativeEpoch::Next => {
                 let current_active_validators =
                     get_active_validator_count(&state.validator_registry, state.current_epoch());
-                let committees_in_current_epoch =
-                    T::get_epoch_committee_count(current_active_validators) as u64;
+                let committees_in_current_epoch = T::get_epoch_committee_count(
+                    current_active_validators,
+                    spec.target_committee_size,
+                ) as u64;
 
                 (state.latest_start_shard + committees_in_current_epoch) % T::shard_count() as u64
             }
diff --git a/eth2/types/src/beacon_state/committee_cache/tests.rs b/eth2/types/src/beacon_state/committee_cache/tests.rs
index ecaa3d457..e9b417e3d 100644
--- a/eth2/types/src/beacon_state/committee_cache/tests.rs
+++ b/eth2/types/src/beacon_state/committee_cache/tests.rs
@@ -20,7 +20,7 @@ fn default_values() {
 }
 
 fn new_state<T: EthSpec>(validator_count: usize, slot: Slot) -> BeaconState<T> {
-    let spec = &T::spec();
+    let spec = &T::default_spec();
 
     let mut builder =
         TestingBeaconStateBuilder::from_single_keypair(validator_count, &Keypair::random(), spec);
@@ -35,7 +35,7 @@ fn new_state<T: EthSpec>(validator_count: usize, slot: Slot) -> BeaconState<T> {
 #[test]
 fn fails_without_validators() {
     let state = new_state::<FewValidatorsEthSpec>(0, Slot::new(0));
-    let spec = &FewValidatorsEthSpec::spec();
+    let spec = &FewValidatorsEthSpec::default_spec();
 
     assert_eq!(
         CommitteeCache::initialized(&state, state.current_epoch(), &spec),
@@ -46,7 +46,7 @@ fn fails_without_validators() {
 #[test]
 fn initializes_with_the_right_epoch() {
     let state = new_state::<FewValidatorsEthSpec>(16, Slot::new(0));
-    let spec = &FewValidatorsEthSpec::spec();
+    let spec = &FewValidatorsEthSpec::default_spec();
 
     let cache = CommitteeCache::default();
     assert_eq!(cache.initialized_epoch, None);
@@ -68,7 +68,7 @@ fn shuffles_for_the_right_epoch() {
     let slot = epoch.start_slot(FewValidatorsEthSpec::slots_per_epoch());
 
     let mut state = new_state::<FewValidatorsEthSpec>(num_validators, slot);
-    let spec = &FewValidatorsEthSpec::spec();
+    let spec = &FewValidatorsEthSpec::default_spec();
 
     let distinct_hashes: Vec<Hash256> = (0..FewValidatorsEthSpec::latest_randao_mixes_length())
         .into_iter()
@@ -123,7 +123,7 @@ fn can_start_on_any_shard() {
     let slot = epoch.start_slot(FewValidatorsEthSpec::slots_per_epoch());
 
     let mut state = new_state::<FewValidatorsEthSpec>(num_validators, slot);
-    let spec = &FewValidatorsEthSpec::spec();
+    let spec = &FewValidatorsEthSpec::default_spec();
 
     for i in 0..FewValidatorsEthSpec::shard_count() as u64 {
         state.latest_start_shard = i;
@@ -150,15 +150,17 @@ impl EthSpec for ExcessShardsEthSpec {
     type LatestRandaoMixesLength = U8192;
     type LatestActiveIndexRootsLength = U8192;
     type LatestSlashedExitLength = U8192;
+    type SlotsPerEpoch = U8;
+    type GenesisEpoch = U0;
 
-    fn spec() -> ChainSpec {
-        ChainSpec::few_validators()
+    fn default_spec() -> ChainSpec {
+        ChainSpec::few_validators(Self::slots_per_epoch())
     }
 }
 
 #[test]
 fn starts_on_the_correct_shard() {
-    let spec = &ExcessShardsEthSpec::spec();
+    let spec = &ExcessShardsEthSpec::default_spec();
 
     let num_validators = ExcessShardsEthSpec::shard_count();
 
@@ -200,14 +202,16 @@ fn starts_on_the_correct_shard() {
 
     let previous_shards = ExcessShardsEthSpec::get_epoch_committee_count(
         get_active_validator_count(&state.validator_registry, previous_epoch),
+        spec.target_committee_size,
     );
     let current_shards = ExcessShardsEthSpec::get_epoch_committee_count(
         get_active_validator_count(&state.validator_registry, current_epoch),
+        spec.target_committee_size,
+    );
+    let next_shards = ExcessShardsEthSpec::get_epoch_committee_count(
+        get_active_validator_count(&state.validator_registry, next_epoch),
+        spec.target_committee_size,
     );
-    let next_shards = ExcessShardsEthSpec::get_epoch_committee_count(get_active_validator_count(
-        &state.validator_registry,
-        next_epoch,
-    ));
 
     assert_eq!(
         previous_shards as usize,
diff --git a/eth2/types/src/beacon_state/tests.rs b/eth2/types/src/beacon_state/tests.rs
index 588d24aa8..581b9662e 100644
--- a/eth2/types/src/beacon_state/tests.rs
+++ b/eth2/types/src/beacon_state/tests.rs
@@ -7,7 +7,7 @@ ssz_tests!(FoundationBeaconState);
 cached_tree_hash_tests!(FoundationBeaconState);
 
 fn test_beacon_proposer_index<T: EthSpec>() {
-    let spec = T::spec();
+    let spec = T::default_spec();
     let relative_epoch = RelativeEpoch::Current;
 
     // Build a state for testing.
@@ -61,7 +61,7 @@ fn beacon_proposer_index() {
 /// (current_epoch - LATEST_ACTIVE_INDEX_ROOTS_LENGTH + ACTIVATION_EXIT_DELAY, current_epoch +
 /// ACTIVATION_EXIT_DELAY]
 fn active_index_range<T: EthSpec>(current_epoch: Epoch) -> RangeInclusive<Epoch> {
-    let delay = T::spec().activation_exit_delay;
+    let delay = T::default_spec().activation_exit_delay;
 
     let start: i32 =
         current_epoch.as_u64() as i32 - T::latest_active_index_roots() as i32 + delay as i32;
@@ -79,7 +79,7 @@ fn active_index_range<T: EthSpec>(current_epoch: Epoch) -> RangeInclusive<Epoch>
 /// Test getting an active index root at the start and end of the valid range, and one either side
 /// of that range.
 fn test_active_index<T: EthSpec>(state_slot: Slot) {
-    let spec = T::spec();
+    let spec = T::default_spec();
     let builder: TestingBeaconStateBuilder<T> =
         TestingBeaconStateBuilder::from_default_keypairs_file_if_exists(16, &spec);
     let (mut state, _keypairs) = builder.build();
@@ -133,8 +133,8 @@ fn test_cache_initialization<'a, T: EthSpec>(
     spec: &ChainSpec,
 ) {
     let slot = relative_epoch
-        .into_epoch(state.slot.epoch(spec.slots_per_epoch))
-        .start_slot(spec.slots_per_epoch);
+        .into_epoch(state.slot.epoch(T::slots_per_epoch()))
+        .start_slot(T::slots_per_epoch());
 
     // Assuming the cache isn't already built, assert that a call to a cache-using function fails.
     assert_eq!(
@@ -166,13 +166,13 @@ fn test_cache_initialization<'a, T: EthSpec>(
 
 #[test]
 fn cache_initialization() {
-    let spec = FewValidatorsEthSpec::spec();
+    let spec = FewValidatorsEthSpec::default_spec();
 
     let builder: TestingBeaconStateBuilder<FewValidatorsEthSpec> =
         TestingBeaconStateBuilder::from_default_keypairs_file_if_exists(16, &spec);
     let (mut state, _keypairs) = builder.build();
 
-    state.slot = (spec.genesis_epoch + 1).start_slot(spec.slots_per_epoch);
+    state.slot = (spec.genesis_epoch + 1).start_slot(FewValidatorsEthSpec::slots_per_epoch());
 
     test_cache_initialization(&mut state, RelativeEpoch::Previous, &spec);
     test_cache_initialization(&mut state, RelativeEpoch::Current, &spec);
@@ -234,7 +234,7 @@ mod committees {
             (start_shard..start_shard + T::shard_count() as u64).into_iter();
 
         // Loop through all slots in the epoch being tested.
-        for slot in epoch.slot_iter(spec.slots_per_epoch) {
+        for slot in epoch.slot_iter(T::slots_per_epoch()) {
             let crosslink_committees = state.get_crosslink_committees_at_slot(slot).unwrap();
 
             // Assert that the number of committees in this slot is consistent with the reported number
@@ -290,7 +290,7 @@ mod committees {
         state_epoch: Epoch,
         cache_epoch: RelativeEpoch,
     ) {
-        let spec = &T::spec();
+        let spec = &T::default_spec();
 
         let mut builder = TestingBeaconStateBuilder::from_single_keypair(
             validator_count,
@@ -298,7 +298,7 @@ mod committees {
             spec,
         );
 
-        let slot = state_epoch.start_slot(spec.slots_per_epoch);
+        let slot = state_epoch.start_slot(T::slots_per_epoch());
         builder.teleport_to_slot(slot, spec);
 
         let (mut state, _keypairs): (BeaconState<T>, _) = builder.build();
@@ -325,7 +325,7 @@ mod committees {
     }
 
     fn committee_consistency_test_suite<T: EthSpec>(cached_epoch: RelativeEpoch) {
-        let spec = T::spec();
+        let spec = T::default_spec();
 
         let validator_count = (T::shard_count() * spec.target_committee_size) + 1;
 
diff --git a/eth2/types/src/chain_spec.rs b/eth2/types/src/chain_spec.rs
index 20aa6fcdb..d9a0785a1 100644
--- a/eth2/types/src/chain_spec.rs
+++ b/eth2/types/src/chain_spec.rs
@@ -1,6 +1,6 @@
 use crate::*;
 use int_to_bytes::int_to_bytes4;
-use serde_derive::Deserialize;
+use serde_derive::{Deserialize, Serialize};
 use test_utils::u8_from_hex_str;
 
 /// Each of the BLS signature domains.
@@ -18,7 +18,7 @@ pub enum Domain {
 /// Holds all the "constants" for a BeaconChain.
 ///
 /// Spec v0.6.1
-#[derive(PartialEq, Debug, Clone, Deserialize)]
+#[derive(PartialEq, Debug, Clone, Serialize, Deserialize)]
 #[serde(default)]
 pub struct ChainSpec {
     /*
@@ -59,7 +59,7 @@ pub struct ChainSpec {
      */
     pub seconds_per_slot: u64,
     pub min_attestation_inclusion_delay: u64,
-    pub slots_per_epoch: u64,
+    //pub slots_per_epoch: u64,
     pub min_seed_lookahead: Epoch,
     pub activation_exit_delay: u64,
     pub slots_per_eth1_voting_period: u64,
@@ -137,7 +137,7 @@ impl ChainSpec {
     /// Returns a `ChainSpec` compatible with the Ethereum Foundation specification.
     ///
     /// Spec v0.6.1
-    pub(crate) fn foundation() -> Self {
+    pub fn foundation() -> Self {
         Self {
             /*
              * Misc
@@ -176,7 +176,7 @@ impl ChainSpec {
              */
             seconds_per_slot: 6,
             min_attestation_inclusion_delay: 4,
-            slots_per_epoch: 64,
+            // slots_per_epoch: 64,
             min_seed_lookahead: Epoch::new(1),
             activation_exit_delay: 4,
             slots_per_eth1_voting_period: 1_024,
@@ -226,7 +226,7 @@ impl ChainSpec {
     /// Returns a `ChainSpec` compatible with the Lighthouse testnet specification.
     ///
     /// Spec v0.4.0
-    pub(crate) fn lighthouse_testnet() -> Self {
+    pub fn lighthouse_testnet(slots_per_epoch: u64) -> Self {
         /*
          * Lighthouse testnet bootnodes
          */
@@ -237,21 +237,19 @@ impl ChainSpec {
         Self {
             boot_nodes,
             chain_id: 2, // lighthouse testnet chain id
-            ..ChainSpec::few_validators()
+            ..ChainSpec::few_validators(slots_per_epoch)
         }
     }
 
     /// Returns a `ChainSpec` compatible with the specification suitable for 8 validators.
-    pub(crate) fn few_validators() -> Self {
+    pub fn few_validators(slots_per_epoch: u64) -> Self {
         let genesis_slot = Slot::new(0);
-        let slots_per_epoch = 8;
         let genesis_epoch = genesis_slot.epoch(slots_per_epoch);
 
         Self {
             target_committee_size: 1,
             genesis_slot,
             genesis_epoch,
-            slots_per_epoch,
             ..ChainSpec::foundation()
         }
     }
diff --git a/eth2/types/src/test_utils/builders/testing_attestation_data_builder.rs b/eth2/types/src/test_utils/builders/testing_attestation_data_builder.rs
index 2150f5433..0b4aa2987 100644
--- a/eth2/types/src/test_utils/builders/testing_attestation_data_builder.rs
+++ b/eth2/types/src/test_utils/builders/testing_attestation_data_builder.rs
@@ -21,7 +21,7 @@ impl TestingAttestationDataBuilder {
         let previous_epoch = state.previous_epoch();
 
         let is_previous_epoch =
-            state.slot.epoch(spec.slots_per_epoch) != slot.epoch(spec.slots_per_epoch);
+            state.slot.epoch(T::slots_per_epoch()) != slot.epoch(T::slots_per_epoch());
 
         let source_epoch = if is_previous_epoch {
             state.previous_justified_epoch
@@ -37,11 +37,11 @@ impl TestingAttestationDataBuilder {
 
         let target_root = if is_previous_epoch {
             *state
-                .get_block_root(previous_epoch.start_slot(spec.slots_per_epoch))
+                .get_block_root(previous_epoch.start_slot(T::slots_per_epoch()))
                 .unwrap()
         } else {
             *state
-                .get_block_root(current_epoch.start_slot(spec.slots_per_epoch))
+                .get_block_root(current_epoch.start_slot(T::slots_per_epoch()))
                 .unwrap()
         };
 
@@ -57,7 +57,7 @@ impl TestingAttestationDataBuilder {
         };
 
         let source_root = *state
-            .get_block_root(source_epoch.start_slot(spec.slots_per_epoch))
+            .get_block_root(source_epoch.start_slot(T::slots_per_epoch()))
             .unwrap();
 
         let data = AttestationData {
diff --git a/eth2/types/src/test_utils/builders/testing_beacon_block_builder.rs b/eth2/types/src/test_utils/builders/testing_beacon_block_builder.rs
index 941ad8fdd..999e88aae 100644
--- a/eth2/types/src/test_utils/builders/testing_beacon_block_builder.rs
+++ b/eth2/types/src/test_utils/builders/testing_beacon_block_builder.rs
@@ -36,9 +36,9 @@ impl TestingBeaconBlockBuilder {
     /// Signs the block.
     ///
     /// Modifying the block after signing may invalidate the signature.
-    pub fn sign(&mut self, sk: &SecretKey, fork: &Fork, spec: &ChainSpec) {
+    pub fn sign<T: EthSpec>(&mut self, sk: &SecretKey, fork: &Fork, spec: &ChainSpec) {
         let message = self.block.signed_root();
-        let epoch = self.block.slot.epoch(spec.slots_per_epoch);
+        let epoch = self.block.slot.epoch(T::slots_per_epoch());
         let domain = spec.get_domain(epoch, Domain::BeaconProposer, fork);
         self.block.signature = Signature::new(&message, domain, sk);
     }
@@ -46,8 +46,8 @@ impl TestingBeaconBlockBuilder {
     /// Sets the randao to be a signature across the blocks epoch.
     ///
     /// Modifying the block's slot after signing may invalidate the signature.
-    pub fn set_randao_reveal(&mut self, sk: &SecretKey, fork: &Fork, spec: &ChainSpec) {
-        let epoch = self.block.slot.epoch(spec.slots_per_epoch);
+    pub fn set_randao_reveal<T: EthSpec>(&mut self, sk: &SecretKey, fork: &Fork, spec: &ChainSpec) {
+        let epoch = self.block.slot.epoch(T::slots_per_epoch());
         let message = epoch.tree_hash_root();
         let domain = spec.get_domain(epoch, Domain::Randao, fork);
         self.block.body.randao_reveal = Signature::new(&message, domain, sk);
@@ -59,14 +59,15 @@ impl TestingBeaconBlockBuilder {
     }
 
     /// Inserts a signed, valid `ProposerSlashing` for the validator.
-    pub fn insert_proposer_slashing(
+    pub fn insert_proposer_slashing<T: EthSpec>(
         &mut self,
         validator_index: u64,
         secret_key: &SecretKey,
         fork: &Fork,
         spec: &ChainSpec,
     ) {
-        let proposer_slashing = build_proposer_slashing(validator_index, secret_key, fork, spec);
+        let proposer_slashing =
+            build_proposer_slashing::<T>(validator_index, secret_key, fork, spec);
         self.block.body.proposer_slashings.push(proposer_slashing);
     }
 
@@ -115,7 +116,7 @@ impl TestingBeaconBlockBuilder {
         // - The slot is too old to be included in a block at this slot.
         // - The `MAX_ATTESTATIONS`.
         loop {
-            if state.slot >= slot + spec.slots_per_epoch {
+            if state.slot >= slot + T::slots_per_epoch() {
                 break;
             }
 
@@ -194,7 +195,7 @@ impl TestingBeaconBlockBuilder {
         builder.set_index(index);
         builder.sign(
             &keypair,
-            state.slot.epoch(spec.slots_per_epoch),
+            state.slot.epoch(T::slots_per_epoch()),
             &state.fork,
             spec,
         );
@@ -211,7 +212,7 @@ impl TestingBeaconBlockBuilder {
         spec: &ChainSpec,
     ) {
         let mut builder = TestingVoluntaryExitBuilder::new(
-            state.slot.epoch(spec.slots_per_epoch),
+            state.slot.epoch(T::slots_per_epoch()),
             validator_index,
         );
 
@@ -234,14 +235,19 @@ impl TestingBeaconBlockBuilder {
         spec: &ChainSpec,
     ) {
         let mut builder = TestingTransferBuilder::new(from, to, amount, state.slot);
-        builder.sign(keypair, &state.fork, spec);
+        builder.sign::<T>(keypair, &state.fork, spec);
 
         self.block.body.transfers.push(builder.build())
     }
 
     /// Signs and returns the block, consuming the builder.
-    pub fn build(mut self, sk: &SecretKey, fork: &Fork, spec: &ChainSpec) -> BeaconBlock {
-        self.sign(sk, fork, spec);
+    pub fn build<T: EthSpec>(
+        mut self,
+        sk: &SecretKey,
+        fork: &Fork,
+        spec: &ChainSpec,
+    ) -> BeaconBlock {
+        self.sign::<T>(sk, fork, spec);
         self.block
     }
 
@@ -254,7 +260,7 @@ impl TestingBeaconBlockBuilder {
 /// Builds an `ProposerSlashing` for some `validator_index`.
 ///
 /// Signs the message using a `BeaconChainHarness`.
-fn build_proposer_slashing(
+fn build_proposer_slashing<T: EthSpec>(
     validator_index: u64,
     secret_key: &SecretKey,
     fork: &Fork,
@@ -265,7 +271,7 @@ fn build_proposer_slashing(
         Signature::new(message, domain, secret_key)
     };
 
-    TestingProposerSlashingBuilder::double_vote(validator_index, signer, spec)
+    TestingProposerSlashingBuilder::double_vote::<T, _>(validator_index, signer, spec)
 }
 
 /// Builds an `AttesterSlashing` for some `validator_indices`.
diff --git a/eth2/types/src/test_utils/builders/testing_beacon_state_builder.rs b/eth2/types/src/test_utils/builders/testing_beacon_state_builder.rs
index 20ed8a893..dc2dd0a7c 100644
--- a/eth2/types/src/test_utils/builders/testing_beacon_state_builder.rs
+++ b/eth2/types/src/test_utils/builders/testing_beacon_state_builder.rs
@@ -173,7 +173,7 @@ impl<T: EthSpec> TestingBeaconStateBuilder<T> {
 
     /// Sets the `BeaconState` to be in a slot, calling `teleport_to_epoch` to update the epoch.
     pub fn teleport_to_slot(&mut self, slot: Slot, spec: &ChainSpec) {
-        self.teleport_to_epoch(slot.epoch(spec.slots_per_epoch), spec);
+        self.teleport_to_epoch(slot.epoch(T::slots_per_epoch()), spec);
         self.state.slot = slot;
     }
 
@@ -184,7 +184,7 @@ impl<T: EthSpec> TestingBeaconStateBuilder<T> {
     fn teleport_to_epoch(&mut self, epoch: Epoch, spec: &ChainSpec) {
         let state = &mut self.state;
 
-        let slot = epoch.start_slot(spec.slots_per_epoch);
+        let slot = epoch.start_slot(T::slots_per_epoch());
 
         state.slot = slot;
 
@@ -214,8 +214,8 @@ impl<T: EthSpec> TestingBeaconStateBuilder<T> {
         let current_epoch = state.current_epoch();
         let previous_epoch = state.previous_epoch();
 
-        let first_slot = previous_epoch.start_slot(spec.slots_per_epoch).as_u64();
-        let last_slot = current_epoch.end_slot(spec.slots_per_epoch).as_u64()
+        let first_slot = previous_epoch.start_slot(T::slots_per_epoch()).as_u64();
+        let last_slot = current_epoch.end_slot(T::slots_per_epoch()).as_u64()
             - spec.min_attestation_inclusion_delay;
         let last_slot = std::cmp::min(state.slot.as_u64(), last_slot);
 
diff --git a/eth2/types/src/test_utils/builders/testing_proposer_slashing_builder.rs b/eth2/types/src/test_utils/builders/testing_proposer_slashing_builder.rs
index 458082de2..99c005472 100644
--- a/eth2/types/src/test_utils/builders/testing_proposer_slashing_builder.rs
+++ b/eth2/types/src/test_utils/builders/testing_proposer_slashing_builder.rs
@@ -17,8 +17,9 @@ impl TestingProposerSlashingBuilder {
     /// - `domain: Domain`
     ///
     /// Where domain is a domain "constant" (e.g., `spec.domain_attestation`).
-    pub fn double_vote<F>(proposer_index: u64, signer: F, spec: &ChainSpec) -> ProposerSlashing
+    pub fn double_vote<T, F>(proposer_index: u64, signer: F, spec: &ChainSpec) -> ProposerSlashing
     where
+        T: EthSpec,
         F: Fn(u64, &[u8], Epoch, Domain) -> Signature,
     {
         let slot = Slot::new(0);
@@ -40,13 +41,13 @@ impl TestingProposerSlashingBuilder {
 
         header_1.signature = {
             let message = header_1.signed_root();
-            let epoch = slot.epoch(spec.slots_per_epoch);
+            let epoch = slot.epoch(T::slots_per_epoch());
             signer(proposer_index, &message[..], epoch, Domain::BeaconProposer)
         };
 
         header_2.signature = {
             let message = header_2.signed_root();
-            let epoch = slot.epoch(spec.slots_per_epoch);
+            let epoch = slot.epoch(T::slots_per_epoch());
             signer(proposer_index, &message[..], epoch, Domain::BeaconProposer)
         };
 
diff --git a/eth2/types/src/test_utils/builders/testing_transfer_builder.rs b/eth2/types/src/test_utils/builders/testing_transfer_builder.rs
index 2680f7b66..d3c3da19e 100644
--- a/eth2/types/src/test_utils/builders/testing_transfer_builder.rs
+++ b/eth2/types/src/test_utils/builders/testing_transfer_builder.rs
@@ -29,10 +29,10 @@ impl TestingTransferBuilder {
     /// Signs the transfer.
     ///
     /// The keypair must match that of the `from` validator index.
-    pub fn sign(&mut self, keypair: Keypair, fork: &Fork, spec: &ChainSpec) {
+    pub fn sign<T: EthSpec>(&mut self, keypair: Keypair, fork: &Fork, spec: &ChainSpec) {
         self.transfer.pubkey = keypair.pk;
         let message = self.transfer.signed_root();
-        let epoch = self.transfer.slot.epoch(spec.slots_per_epoch);
+        let epoch = self.transfer.slot.epoch(T::slots_per_epoch());
         let domain = spec.get_domain(epoch, Domain::Transfer, fork);
 
         self.transfer.signature = Signature::new(&message, domain, &keypair.sk);
diff --git a/tests/ef_tests/src/cases/epoch_processing_crosslinks.rs b/tests/ef_tests/src/cases/epoch_processing_crosslinks.rs
index fa530f9ad..afdb9cc31 100644
--- a/tests/ef_tests/src/cases/epoch_processing_crosslinks.rs
+++ b/tests/ef_tests/src/cases/epoch_processing_crosslinks.rs
@@ -29,9 +29,9 @@ impl<E: EthSpec> Case for EpochProcessingCrosslinks<E> {
         let mut expected = self.post.clone();
 
         // Processing requires the epoch cache.
-        state.build_all_caches(&E::spec()).unwrap();
+        state.build_all_caches(&E::default_spec()).unwrap();
 
-        let mut result = process_crosslinks(&mut state, &E::spec()).map(|_| state);
+        let mut result = process_crosslinks(&mut state, &E::default_spec()).map(|_| state);
 
         compare_beacon_state_results_without_caches(&mut result, &mut expected)
     }
diff --git a/tests/ef_tests/src/cases/epoch_processing_registry_updates.rs b/tests/ef_tests/src/cases/epoch_processing_registry_updates.rs
index d91a7a4c3..092a8a709 100644
--- a/tests/ef_tests/src/cases/epoch_processing_registry_updates.rs
+++ b/tests/ef_tests/src/cases/epoch_processing_registry_updates.rs
@@ -27,7 +27,7 @@ impl<E: EthSpec> Case for EpochProcessingRegistryUpdates<E> {
     fn result(&self, _case_index: usize) -> Result<(), Error> {
         let mut state = self.pre.clone();
         let mut expected = self.post.clone();
-        let spec = &E::spec();
+        let spec = &E::default_spec();
 
         // Processing requires the epoch cache.
         state.build_all_caches(spec).unwrap();
diff --git a/tests/ef_tests/src/cases/operations_attester_slashing.rs b/tests/ef_tests/src/cases/operations_attester_slashing.rs
index d8f1f06dc..1b95f4359 100644
--- a/tests/ef_tests/src/cases/operations_attester_slashing.rs
+++ b/tests/ef_tests/src/cases/operations_attester_slashing.rs
@@ -31,9 +31,10 @@ impl<E: EthSpec> Case for OperationsAttesterSlashing<E> {
         let mut expected = self.post.clone();
 
         // Processing requires the epoch cache.
-        state.build_all_caches(&E::spec()).unwrap();
+        state.build_all_caches(&E::default_spec()).unwrap();
 
-        let result = process_attester_slashings(&mut state, &[attester_slashing], &E::spec());
+        let result =
+            process_attester_slashings(&mut state, &[attester_slashing], &E::default_spec());
 
         let mut result = result.and_then(|_| Ok(state));
 
diff --git a/tests/ef_tests/src/cases/operations_deposit.rs b/tests/ef_tests/src/cases/operations_deposit.rs
index 23b791ba5..8100590fd 100644
--- a/tests/ef_tests/src/cases/operations_deposit.rs
+++ b/tests/ef_tests/src/cases/operations_deposit.rs
@@ -34,7 +34,7 @@ impl<E: EthSpec> Case for OperationsDeposit<E> {
         let deposit = self.deposit.clone();
         let mut expected = self.post.clone();
 
-        let result = process_deposits(&mut state, &[deposit], &E::spec());
+        let result = process_deposits(&mut state, &[deposit], &E::default_spec());
 
         let mut result = result.and_then(|_| Ok(state));
 
diff --git a/tests/ef_tests/src/cases/operations_exit.rs b/tests/ef_tests/src/cases/operations_exit.rs
index 3d0f6b010..cfe20d82b 100644
--- a/tests/ef_tests/src/cases/operations_exit.rs
+++ b/tests/ef_tests/src/cases/operations_exit.rs
@@ -31,9 +31,9 @@ impl<E: EthSpec> Case for OperationsExit<E> {
         let mut expected = self.post.clone();
 
         // Exit processing requires the epoch cache.
-        state.build_all_caches(&E::spec()).unwrap();
+        state.build_all_caches(&E::default_spec()).unwrap();
 
-        let result = process_exits(&mut state, &[exit], &E::spec());
+        let result = process_exits(&mut state, &[exit], &E::default_spec());
 
         let mut result = result.and_then(|_| Ok(state));
 
diff --git a/tests/ef_tests/src/cases/operations_proposer_slashing.rs b/tests/ef_tests/src/cases/operations_proposer_slashing.rs
index 416a6f7c3..43293dfbc 100644
--- a/tests/ef_tests/src/cases/operations_proposer_slashing.rs
+++ b/tests/ef_tests/src/cases/operations_proposer_slashing.rs
@@ -31,9 +31,10 @@ impl<E: EthSpec> Case for OperationsProposerSlashing<E> {
         let mut expected = self.post.clone();
 
         // Processing requires the epoch cache.
-        state.build_all_caches(&E::spec()).unwrap();
+        state.build_all_caches(&E::default_spec()).unwrap();
 
-        let result = process_proposer_slashings(&mut state, &[proposer_slashing], &E::spec());
+        let result =
+            process_proposer_slashings(&mut state, &[proposer_slashing], &E::default_spec());
 
         let mut result = result.and_then(|_| Ok(state));
 
diff --git a/tests/ef_tests/src/cases/operations_transfer.rs b/tests/ef_tests/src/cases/operations_transfer.rs
index 3ec96cd5c..66318e750 100644
--- a/tests/ef_tests/src/cases/operations_transfer.rs
+++ b/tests/ef_tests/src/cases/operations_transfer.rs
@@ -31,9 +31,9 @@ impl<E: EthSpec> Case for OperationsTransfer<E> {
         let mut expected = self.post.clone();
 
         // Transfer processing requires the epoch cache.
-        state.build_all_caches(&E::spec()).unwrap();
+        state.build_all_caches(&E::default_spec()).unwrap();
 
-        let mut spec = E::spec();
+        let mut spec = E::default_spec();
         spec.max_transfers = 1;
 
         let result = process_transfers(&mut state, &[transfer], &spec);
diff --git a/tests/ef_tests/src/cases/shuffling.rs b/tests/ef_tests/src/cases/shuffling.rs
index ef8a1b934..2920840c8 100644
--- a/tests/ef_tests/src/cases/shuffling.rs
+++ b/tests/ef_tests/src/cases/shuffling.rs
@@ -24,7 +24,7 @@ impl<T: EthSpec> Case for Shuffling<T> {
         if self.count == 0 {
             compare_result::<_, Error>(&Ok(vec![]), &Some(self.shuffled.clone()))?;
         } else {
-            let spec = T::spec();
+            let spec = T::default_spec();
             let seed = hex::decode(&self.seed[2..])
                 .map_err(|e| Error::FailedToParseTest(format!("{:?}", e)))?;
 
diff --git a/tests/ef_tests/src/eth_specs.rs b/tests/ef_tests/src/eth_specs.rs
index cdf8b94e8..f0ee1e9f0 100644
--- a/tests/ef_tests/src/eth_specs.rs
+++ b/tests/ef_tests/src/eth_specs.rs
@@ -1,6 +1,6 @@
 use serde_derive::{Deserialize, Serialize};
 use types::{
-    typenum::{U64, U8},
+    typenum::{U0, U64, U8},
     ChainSpec, EthSpec, FewValidatorsEthSpec, FoundationEthSpec,
 };
 
@@ -18,10 +18,12 @@ impl EthSpec for MinimalEthSpec {
     type LatestRandaoMixesLength = U64;
     type LatestActiveIndexRootsLength = U64;
     type LatestSlashedExitLength = U64;
+    type SlotsPerEpoch = U8;
+    type GenesisEpoch = U0;
 
-    fn spec() -> ChainSpec {
+    fn default_spec() -> ChainSpec {
         // TODO: this spec is likely incorrect!
-        let mut spec = FewValidatorsEthSpec::spec();
+        let mut spec = FewValidatorsEthSpec::default_spec();
         spec.shuffle_round_count = 10;
         spec
     }
diff --git a/validator_client/src/attestation_producer/mod.rs b/validator_client/src/attestation_producer/mod.rs
index 0a65c1f1e..d59f383ef 100644
--- a/validator_client/src/attestation_producer/mod.rs
+++ b/validator_client/src/attestation_producer/mod.rs
@@ -39,6 +39,8 @@ pub struct AttestationProducer<'a, B: BeaconNodeAttestation, S: Signer> {
     pub beacon_node: Arc<B>,
     /// The signer to sign the block.
     pub signer: &'a S,
+    /// Used for caclulating epoch.
+    pub slots_per_epoch: u64,
 }
 
 impl<'a, B: BeaconNodeAttestation, S: Signer> AttestationProducer<'a, B, S> {
@@ -78,7 +80,7 @@ impl<'a, B: BeaconNodeAttestation, S: Signer> AttestationProducer<'a, B, S> {
     /// The slash-protection code is not yet implemented. There is zero protection against
     /// slashing.
     pub fn produce_attestation(&mut self) -> Result<ValidatorEvent, Error> {
-        let epoch = self.duty.slot.epoch(self.spec.slots_per_epoch);
+        let epoch = self.duty.slot.epoch(self.slots_per_epoch);
 
         let attestation = self
             .beacon_node
diff --git a/validator_client/src/block_producer/mod.rs b/validator_client/src/block_producer/mod.rs
index fc01b8126..9c19e3532 100644
--- a/validator_client/src/block_producer/mod.rs
+++ b/validator_client/src/block_producer/mod.rs
@@ -48,6 +48,8 @@ pub struct BlockProducer<'a, B: BeaconNodeBlock, S: Signer> {
     pub beacon_node: Arc<B>,
     /// The signer to sign the block.
     pub signer: &'a S,
+    /// Used for caclulating epoch.
+    pub slots_per_epoch: u64,
 }
 
 impl<'a, B: BeaconNodeBlock, S: Signer> BlockProducer<'a, B, S> {
@@ -84,7 +86,7 @@ impl<'a, B: BeaconNodeBlock, S: Signer> BlockProducer<'a, B, S> {
     /// The slash-protection code is not yet implemented. There is zero protection against
     /// slashing.
     pub fn produce_block(&mut self) -> Result<ValidatorEvent, Error> {
-        let epoch = self.slot.epoch(self.spec.slots_per_epoch);
+        let epoch = self.slot.epoch(self.slots_per_epoch);
 
         let message = epoch.tree_hash_root();
         let randao_reveal = match self.signer.sign_message(
@@ -186,9 +188,9 @@ mod tests {
         let beacon_node = Arc::new(SimulatedBeaconNode::default());
         let signer = Arc::new(LocalSigner::new(Keypair::random()));
 
-        let mut epoch_map = EpochMap::new(spec.slots_per_epoch);
+        let mut epoch_map = EpochMap::new(T::slots_per_epoch());
         let produce_slot = Slot::new(100);
-        let produce_epoch = produce_slot.epoch(spec.slots_per_epoch);
+        let produce_epoch = produce_slot.epoch(T::slots_per_epoch());
         epoch_map.map.insert(produce_epoch, produce_slot);
         let epoch_map = Arc::new(epoch_map);
 
@@ -233,7 +235,7 @@ mod tests {
         );
 
         // In an epoch without known duties...
-        let slot = (produce_epoch.as_u64() + 1) * spec.slots_per_epoch;
+        let slot = (produce_epoch.as_u64() + 1) * T::slots_per_epoch();
         slot_clock.set_slot(slot);
         assert_eq!(
             block_proposer.poll(),
diff --git a/validator_client/src/config.rs b/validator_client/src/config.rs
index 1e9450d59..f5d795ede 100644
--- a/validator_client/src/config.rs
+++ b/validator_client/src/config.rs
@@ -19,6 +19,7 @@ pub struct Config {
     pub server: String,
     /// The chain specification that we are connecting to
     pub spec: ChainSpec,
+    pub slots_per_epoch: u64,
 }
 
 const DEFAULT_PRIVATE_KEY_FILENAME: &str = "private.key";
@@ -33,12 +34,13 @@ impl Default for Config {
 
         let server = "localhost:5051".to_string();
 
-        let spec = FoundationEthSpec::spec();
+        let spec = FoundationEthSpec::default_spec();
 
         Self {
             data_dir,
             server,
             spec,
+            slots_per_epoch: FoundationEthSpec::slots_per_epoch(),
         }
     }
 }
@@ -67,9 +69,9 @@ impl Config {
         if let Some(spec_str) = args.value_of("spec") {
             info!(log, "Using custom spec: {:?}", spec_str);
             config.spec = match spec_str {
-                "foundation" => FoundationEthSpec::spec(),
-                "few_validators" => FewValidatorsEthSpec::spec(),
-                "lighthouse_testnet" => LighthouseTestnetEthSpec::spec(),
+                "foundation" => FoundationEthSpec::default_spec(),
+                "few_validators" => FewValidatorsEthSpec::default_spec(),
+                "lighthouse_testnet" => LighthouseTestnetEthSpec::default_spec(),
                 // Should be impossible due to clap's `possible_values(..)` function.
                 _ => unreachable!(),
             };
diff --git a/validator_client/src/duties/mod.rs b/validator_client/src/duties/mod.rs
index b2ddfd0b0..3f75c937d 100644
--- a/validator_client/src/duties/mod.rs
+++ b/validator_client/src/duties/mod.rs
@@ -164,7 +164,7 @@ mod tests {
     #[test]
     pub fn polling() {
         let spec = Arc::new(ChainSpec::foundation());
-        let duties_map = Arc::new(EpochDutiesMap::new(spec.slots_per_epoch));
+        let duties_map = Arc::new(EpochDutiesMap::new(T::slots_per_epoch()));
         let keypair = Keypair::random();
         let slot_clock = Arc::new(TestingSlotClock::new(0));
         let beacon_node = Arc::new(TestBeaconNode::default());
diff --git a/validator_client/src/service.rs b/validator_client/src/service.rs
index 033394a0d..99455808c 100644
--- a/validator_client/src/service.rs
+++ b/validator_client/src/service.rs
@@ -47,6 +47,7 @@ pub struct Service<B: BeaconNodeDuties + 'static, S: Signer + 'static> {
     slot_clock: SystemTimeSlotClock,
     /// The current slot we are processing.
     current_slot: Slot,
+    slots_per_epoch: u64,
     /// The chain specification for this clients instance.
     spec: Arc<ChainSpec>,
     /// The duties manager which maintains the state of when to perform actions.
@@ -177,7 +178,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
         // Builds a mapping of Epoch -> Map(PublicKey, EpochDuty)
         // where EpochDuty contains slot numbers and attestation data that each validator needs to
         // produce work on.
-        let duties_map = RwLock::new(EpochDutiesMap::new(config.spec.slots_per_epoch));
+        let duties_map = RwLock::new(EpochDutiesMap::new(config.slots_per_epoch));
 
         // builds a manager which maintains the list of current duties for all known validators
         // and can check when a validator needs to perform a task.
@@ -194,6 +195,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
             fork,
             slot_clock,
             current_slot,
+            slots_per_epoch: config.slots_per_epoch,
             spec,
             duties_manager,
             beacon_block_client,
@@ -204,7 +206,10 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
 
     /// Initialise the service then run the core thread.
     // TODO: Improve handling of generic BeaconNode types, to stub grpcClient
-    pub fn start(config: ValidatorConfig, log: slog::Logger) -> error_chain::Result<()> {
+    pub fn start(
+        config: ValidatorConfig,
+        log: slog::Logger,
+    ) -> error_chain::Result<()> {
         // connect to the node and retrieve its properties and initialize the gRPC clients
         let mut service =
             Service::<ValidatorServiceClient, Keypair>::initialize_service(config, log)?;
@@ -274,7 +279,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
             Ok(slot) => slot.expect("Genesis is in the future"),
         };
 
-        let current_epoch = current_slot.epoch(self.spec.slots_per_epoch);
+        let current_epoch = current_slot.epoch(self.slots_per_epoch);
 
         // this is a fatal error. If the slot clock repeats, there is something wrong with
         // the timer, terminate immediately.
@@ -291,7 +296,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
     fn check_for_duties(&mut self) {
         let cloned_manager = self.duties_manager.clone();
         let cloned_log = self.log.clone();
-        let current_epoch = self.current_slot.epoch(self.spec.slots_per_epoch);
+        let current_epoch = self.current_slot.epoch(self.slots_per_epoch);
         // spawn a new thread separate to the runtime
         // TODO: Handle thread termination/timeout
         // TODO: Add duties thread back in, with channel to process duties in duty change.
@@ -316,6 +321,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
                     let spec = self.spec.clone();
                     let beacon_node = self.beacon_block_client.clone();
                     let log = self.log.clone();
+                    let slots_per_epoch = self.slots_per_epoch;
                     std::thread::spawn(move || {
                         info!(log, "Producing a block"; "Validator"=> format!("{}", signers[signer_index]));
                         let signer = &signers[signer_index];
@@ -325,6 +331,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
                             spec,
                             beacon_node,
                             signer,
+                            slots_per_epoch,
                         };
                         block_producer.handle_produce_block(log);
                     });
@@ -337,6 +344,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
                     let spec = self.spec.clone();
                     let beacon_node = self.attestation_client.clone();
                     let log = self.log.clone();
+                    let slots_per_epoch = self.slots_per_epoch;
                     std::thread::spawn(move || {
                         info!(log, "Producing an attestation"; "Validator"=> format!("{}", signers[signer_index]));
                         let signer = &signers[signer_index];
@@ -346,6 +354,7 @@ impl<B: BeaconNodeDuties + 'static, S: Signer + 'static> Service<B, S> {
                             spec,
                             beacon_node,
                             signer,
+                            slots_per_epoch,
                         };
                         attestation_producer.handle_produce_attestation(log);
                     });