diff --git a/beacon_chain/consensus_object_pools/block_pools_types.nim b/beacon_chain/consensus_object_pools/block_pools_types.nim
index 5e814c543..1e001f6e0 100644
--- a/beacon_chain/consensus_object_pools/block_pools_types.nim
+++ b/beacon_chain/consensus_object_pools/block_pools_types.nim
@@ -1,5 +1,5 @@
 # beacon_chain
-# Copyright (c) 2018-2020 Status Research & Development GmbH
+# Copyright (c) 2018-2021 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
@@ -9,7 +9,7 @@
 
 import
   # Standard library
-  std/[deques, strformat, sets, tables, hashes],
+  std/[strformat, sets, tables, hashes],
   # Status libraries
   stew/[endians2, byteutils], chronicles,
   eth/keys,
diff --git a/beacon_chain/spec/datatypes/altair.nim b/beacon_chain/spec/datatypes/altair.nim
index 518b8c975..3a624e524 100644
--- a/beacon_chain/spec/datatypes/altair.nim
+++ b/beacon_chain/spec/datatypes/altair.nim
@@ -45,7 +45,20 @@ const
   TARGET_AGGREGATORS_PER_SYNC_SUBCOMMITTEE* = 4
   SYNC_COMMITTEE_SUBNET_COUNT* = 8
 
+let
+  # https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#misc
+  # Cannot be computed at compile-time due to importc dependency
+  G2_POINT_AT_INFINITY* = ValidatorSig.fromRaw([
+    0xc0'u8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+          0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+          0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+          0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+          0, 0, 0, 0])
+
 type
+  # https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#custom-types
+  ParticipationFlags* = distinct uint8
+
   # https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#syncaggregate
   SyncAggregate* = object
     sync_committee_bits*: BitArray[SYNC_COMMITTEE_SIZE]
@@ -110,7 +123,13 @@ type
     subcommittee_index*: uint64
 
   # https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#participation-flag-indices
-  ValidatorFlag* = enum
-    TIMELY_HEAD_FLAG = 0
-    TIMELY_SOURCE_FLAG = 1
-    TIMELY_TARGET_FLAG = 2
+  ParticipationFlag* = enum
+    TIMELY_HEAD_FLAG_INDEX = 0
+    TIMELY_SOURCE_FLAG_INDEX = 1
+    TIMELY_TARGET_FLAG_INDEX = 2
+
+# TODO when https://github.com/nim-lang/Nim/issues/14440 lands in Status's Nim,
+# switch proc {.noSideEffect.} to func.
+proc `or`*(x, y: ParticipationFlags) : ParticipationFlags {.borrow, noSideEffect.}
+proc `and`*(x, y: ParticipationFlags) : ParticipationFlags {.borrow, noSideEffect.}
+proc `==`*(x, y: ParticipationFlags) : bool {.borrow, noSideEffect.}
diff --git a/beacon_chain/spec/datatypes/base.nim b/beacon_chain/spec/datatypes/base.nim
index 0bb8a3765..8e0996f0c 100644
--- a/beacon_chain/spec/datatypes/base.nim
+++ b/beacon_chain/spec/datatypes/base.nim
@@ -120,10 +120,12 @@ type
     DOMAIN_SELECTION_PROOF = 5
     DOMAIN_AGGREGATE_AND_PROOF = 6
 
-    # https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.1/configs/mainnet/altair.yaml#L31
+    # https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#domain-types
     # Needs to be in same enum definition and is safe regardless of whether one
     # only accesses phase 0 definitions
     DOMAIN_SYNC_COMMITTEE = 7
+    DOMAIN_SYNC_COMMITTEE_SELECTION_PROOF = 8
+    DOMAIN_CONTRIBUTION_AND_PROOF = 9
 
   # https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#custom-types
   Eth2Domain* = array[32, byte]
diff --git a/beacon_chain/spec/helpers.nim b/beacon_chain/spec/helpers.nim
index 1b46f6da3..1b48807d3 100644
--- a/beacon_chain/spec/helpers.nim
+++ b/beacon_chain/spec/helpers.nim
@@ -15,7 +15,7 @@ import
   # Third-party
   stew/endians2,
   # Internal
-  ./datatypes, ./digest, ./crypto, ../ssz/merkleization
+  ./datatypes/[phase0, altair], ./digest, ./crypto, ../ssz/merkleization
 
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#integer_squareroot
 func integer_squareroot*(n: SomeInteger): SomeInteger =
@@ -178,3 +178,21 @@ func get_seed*(state: BeaconState, epoch: Epoch, domain_type: DomainType): Eth2D
     get_randao_mix(state, # Avoid underflow
       epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1).data
   eth2digest(seed_input)
+
+# https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#get_flag_indices_and_weights
+iterator get_flag_indices_and_weights*(): (ParticipationFlag, int) =
+  for item in [
+      (TIMELY_HEAD_FLAG_INDEX, TIMELY_HEAD_WEIGHT),
+      (TIMELY_SOURCE_FLAG_INDEX, TIMELY_SOURCE_WEIGHT),
+      (TIMELY_TARGET_FLAG_INDEX, TIMELY_TARGET_WEIGHT)]:
+    yield item
+
+# https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#add_flag
+func add_flag*(flags: ParticipationFlags, flag_index: int): ParticipationFlags =
+  let flag = ParticipationFlags(1'u8 shl flag_index)
+  flags or flag
+
+# https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#has_flag
+func has_flag*(flags: ParticipationFlags, flag_index: int): bool =
+  let flag = ParticipationFlags(1'u8 shl flag_index)
+  (flags and flag) == flag
diff --git a/beacon_chain/spec/preset_values.nim b/beacon_chain/spec/preset_values.nim
index d004d05b9..ea8f983a3 100644
--- a/beacon_chain/spec/preset_values.nim
+++ b/beacon_chain/spec/preset_values.nim
@@ -10,10 +10,12 @@ type
     DOMAIN_AGGREGATE_AND_PROOF
     DOMAIN_BEACON_ATTESTER
     DOMAIN_BEACON_PROPOSER
+    DOMAIN_CONTRIBUTION_AND_PROOF
     DOMAIN_DEPOSIT
     DOMAIN_RANDAO
     DOMAIN_SELECTION_PROOF
     DOMAIN_SYNC_COMMITTEE
+    DOMAIN_SYNC_COMMITTEE_SELECTION_PROOF
     DOMAIN_VOLUNTARY_EXIT
     EFFECTIVE_BALANCE_INCREMENT
     EJECTION_BALANCE
diff --git a/beacon_chain/spec/presets.nim b/beacon_chain/spec/presets.nim
index c5d190c12..42fe42a81 100644
--- a/beacon_chain/spec/presets.nim
+++ b/beacon_chain/spec/presets.nim
@@ -63,6 +63,8 @@ const
     DOMAIN_SELECTION_PROOF,
     DOMAIN_AGGREGATE_AND_PROOF,
     DOMAIN_SYNC_COMMITTEE,
+    DOMAIN_SYNC_COMMITTEE_SELECTION_PROOF,
+    DOMAIN_CONTRIBUTION_AND_PROOF,
     CONFIG_NAME
   }
 
diff --git a/beacon_chain/ssz/bytes_reader.nim b/beacon_chain/ssz/bytes_reader.nim
index d18150939..db1df1ed8 100644
--- a/beacon_chain/ssz/bytes_reader.nim
+++ b/beacon_chain/ssz/bytes_reader.nim
@@ -1,5 +1,5 @@
 # beacon_chain
-# Copyright (c) 2018-2020 Status Research & Development GmbH
+# Copyright (c) 2018-2021 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
@@ -11,7 +11,7 @@
 
 import
   std/[typetraits, options],
-  stew/[bitops2, endians2, objects],
+  stew/[endians2, objects],
   ../spec/[digest, datatypes], ./types, ./spec_types, ./merkleization
 
 template raiseIncorrectSize(T: type) =
diff --git a/beacon_chain/ssz/ssz_serialization.nim b/beacon_chain/ssz/ssz_serialization.nim
index 4b204a2c2..b76988fb2 100644
--- a/beacon_chain/ssz/ssz_serialization.nim
+++ b/beacon_chain/ssz/ssz_serialization.nim
@@ -13,7 +13,7 @@
 
 import
   std/[typetraits, options],
-  stew/[bitops2, endians2, leb128, objects],
+  stew/[endians2, leb128, objects],
   serialization, serialization/testing/tracing,
   ../spec/[digest, datatypes],
   ./bytes_reader, ./bitseqs, ./types, ./spec_types