diff --git a/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim b/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim
index 61270ccbf..753d4b5d2 100644
--- a/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim
+++ b/beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim
@@ -49,13 +49,17 @@ type
     ProposerSlashing |
     phase0.SignedBeaconBlock |
     altair.SignedBeaconBlock |
-    SignedVoluntaryExit
+    SignedVoluntaryExit |
+    SyncCommitteeIndex
 
   EncodeArrays* =
     seq[ValidatorIndex] |
     seq[Attestation] |
     seq[SignedAggregateAndProof] |
-    seq[RestCommitteeSubscription]
+    seq[RestCommitteeSubscription] |
+    seq[RestSyncCommitteeSubscription] |
+    seq[RestSyncCommitteeMessage] |
+    seq[RestSignedContributionAndProof]
 
   DecodeTypes* =
     DataEnclosedObject |
@@ -874,8 +878,10 @@ proc readValue*(reader: var JsonReader[RestJson],
      raises: [IOError, SerializationError, Defect].} =
   let res = Base10.decode(uint8, reader.readValue(string))
   if res.isOk():
-    # TODO (cheatfate): Here should be present check for maximum value.
-    value = SyncCommitteeIndex(res.get())
+    if res.get() < SYNC_COMMITTEE_SUBNET_COUNT:
+      value = SyncCommitteeIndex(res.get())
+    else:
+      reader.raiseUnexpectedValue("Sync sub-committee index out of rage")
   else:
     reader.raiseUnexpectedValue($res.error())
 
@@ -976,7 +982,7 @@ proc decodeBytes*[T: SszDecodeTypes](t: typedesc[T], value: openarray[byte],
 proc encodeString*(value: string): RestResult[string] =
   ok(value)
 
-proc encodeString*(value: Epoch|Slot|CommitteeIndex): RestResult[string] =
+proc encodeString*(value: Epoch|Slot|CommitteeIndex|SyncCommitteeIndex): RestResult[string] =
   ok(Base10.toString(uint64(value)))
 
 proc encodeString*(value: ValidatorSig): RestResult[string] =
@@ -1214,6 +1220,14 @@ proc decodeString*(t: typedesc[CommitteeIndex],
   let res = ? Base10.decode(uint64, value)
   ok(CommitteeIndex(res))
 
+proc decodeString*(t: typedesc[SyncCommitteeIndex],
+                   value: string): Result[SyncCommitteeIndex, cstring] =
+  let res = ? Base10.decode(uint8, value)
+  if res.get < SYNC_COMMITTEE_SUBNET_COUNT:
+    ok(CommitteeIndex(res))
+  else:
+    err("sync subcommittee index out of range")
+
 proc decodeString*(t: typedesc[Eth2Digest],
                    value: string): Result[Eth2Digest, cstring] =
   if len(value) != RootHashSize + 2:
diff --git a/beacon_chain/spec/eth2_apis/rest_beacon_calls.nim b/beacon_chain/spec/eth2_apis/rest_beacon_calls.nim
index 005884d28..b90971dcf 100644
--- a/beacon_chain/spec/eth2_apis/rest_beacon_calls.nim
+++ b/beacon_chain/spec/eth2_apis/rest_beacon_calls.nim
@@ -258,11 +258,10 @@ proc submitPoolProposerSlashings*(body: ProposerSlashing): RestPlainResponse {.
      meth: MethodPost.}
   ## https://ethereum.github.io/beacon-APIs/#/Beacon/submitPoolProposerSlashings
 
-# TODO Altair
-# proc submitPoolSyncCommitteeSignatures*(body: seq[RestSyncCommitteeSignature]): RestPlainResponse {.
-#      rest, endpoint: "/eth/v1/beacon/pool/sync_committees",
-#      meth: MethodPost.}
-#   ## https://ethereum.github.io/beacon-APIs/#/Beacon/submitPoolSyncCommitteeSignatures
+proc submitPoolSyncCommitteeSignatures*(body: seq[RestSyncCommitteeMessage]): RestPlainResponse {.
+     rest, endpoint: "/eth/v1/beacon/pool/sync_committees",
+     meth: MethodPost.}
+  ## https://ethereum.github.io/beacon-APIs/#/Beacon/submitPoolSyncCommitteeSignatures
 
 proc getPoolVoluntaryExits*(): RestResponse[GetPoolVoluntaryExitsResponse] {.
      rest, endpoint: "/api/eth/v1/beacon/pool/voluntary_exits",
diff --git a/beacon_chain/spec/eth2_apis/rest_types.nim b/beacon_chain/spec/eth2_apis/rest_types.nim
index f48ae5070..f4629aad7 100644
--- a/beacon_chain/spec/eth2_apis/rest_types.nim
+++ b/beacon_chain/spec/eth2_apis/rest_types.nim
@@ -107,6 +107,28 @@ type
     validator_index*: ValidatorIndex
     validator_sync_committee_indices*: seq[SyncCommitteeIndex]
 
+  RestSyncCommitteeMessage* = object
+    slot*: Slot
+    beacon_block_root*: Eth2Digest
+    validator_index*: uint64
+    signature*: ValidatorSig
+
+  RestSyncCommitteeContribution* = object
+    slot*: Slot
+    beacon_block_root*: Eth2Digest
+    subcommittee_index*: uint64
+    aggregation_bits*: SyncCommitteeAggregationBits ##\
+    signature*: ValidatorSig
+
+  RestContributionAndProof* = object
+    aggregator_index*: uint64
+    selection_proof*: ValidatorSig
+    contribution*: RestSyncCommitteeContribution
+
+  RestSignedContributionAndProof* = object
+    message*: RestContributionAndProof
+    signature*: ValidatorSig
+
   RestCommitteeSubscription* = object
     validator_index*: ValidatorIndex
     committee_index*: CommitteeIndex
@@ -291,7 +313,7 @@ type
   RestBlockInfo* = object
     slot*: Slot
     blck* {.serializedFieldName: "block".}: Eth2Digest
-    
+
   RestEpochSyncCommittee* = object
     validators*: seq[ValidatorIndex]
     validator_aggregates*: seq[seq[ValidatorIndex]]
@@ -347,6 +369,7 @@ type
   GetPoolProposerSlashingsResponse* = DataEnclosedObject[seq[ProposerSlashing]]
   GetPoolVoluntaryExitsResponse* = DataEnclosedObject[seq[SignedVoluntaryExit]]
   GetProposerDutiesResponse* = DataRootEnclosedObject[seq[RestProposerDuty]]
+  GetSyncCommitteeDutiesResponse* = DataEnclosedObject[seq[RestSyncCommitteeDuty]]
   GetSpecResponse* = DataEnclosedObject[RestSpec]
   GetStateFinalityCheckpointsResponse* = DataEnclosedObject[RestBeaconStatesFinalityCheckpoints]
   GetStateForkResponse* = DataEnclosedObject[Fork]
diff --git a/beacon_chain/spec/eth2_apis/rest_validator_calls.nim b/beacon_chain/spec/eth2_apis/rest_validator_calls.nim
index ffa6a0320..3377930bb 100644
--- a/beacon_chain/spec/eth2_apis/rest_validator_calls.nim
+++ b/beacon_chain/spec/eth2_apis/rest_validator_calls.nim
@@ -24,11 +24,12 @@ proc getProposerDuties*(epoch: Epoch): RestResponse[GetProposerDutiesResponse] {
      meth: MethodGet.}
   ## https://ethereum.github.io/beacon-APIs/#/Validator/getProposerDuties
 
-# TODO altair
-# proc getSyncCommitteeDuties*(epoch: Epoch): RestResponse[DataRestSyncCommitteeDuties] {.
-#      rest, endpoint: "/eth/v1/validator/duties/sync/{epoch}",
-#      meth: MethodPost.}
-#   ## https://ethereum.github.io/beacon-APIs/#/Validator/getSyncCommitteeDuties
+proc getSyncCommitteeDuties*(epoch: Epoch,
+                             body: seq[ValidatorIndex]
+                            ): RestResponse[GetSyncCommitteeDutiesResponse] {.
+     rest, endpoint: "/eth/v1/validator/duties/sync/{epoch}",
+     meth: MethodPost.}
+  ## https://ethereum.github.io/beacon-APIs/#/Validator/getSyncCommitteeDuties
 
 proc produceBlock*(slot: Slot, randao_reveal: ValidatorSig,
                    graffiti: GraffitiBytes
@@ -68,21 +69,19 @@ proc prepareBeaconCommitteeSubnet*(body: seq[RestCommitteeSubscription]): RestPl
      meth: MethodPost.}
   ## https://ethereum.github.io/beacon-APIs/#/Validator/prepareBeaconCommitteeSubnet
 
-# TODO altair
-# proc prepareSyncCommitteeSubnets*(body: seq[int]
-#                                   ): RestPlainResponse {.
-#      rest, endpoint: "/eth/v1/validator/sync_committee_subscriptions",
-#      meth: MethodPost.}
-#   ## https://ethereum.github.io/beacon-APIs/#/Validator/prepareSyncCommitteeSubnets
+proc prepareSyncCommitteeSubnets*(body: seq[RestSyncCommitteeSubscription]): RestPlainResponse {.
+     rest, endpoint: "/eth/v1/validator/sync_committee_subscriptions",
+     meth: MethodPost.}
+  ## https://ethereum.github.io/beacon-APIs/#/Validator/prepareSyncCommitteeSubnets
 
-# proc produceSyncCommitteeContribution*(body: seq[int]
-#                                   ): RestPlainResponse {.
-#      rest, endpoint: "/eth/v1/validator/sync_committee_contribution",
-#      meth: MethodPost.}
-#   ## https://ethereum.github.io/beacon-APIs/#/Validator/produceSyncCommitteeContribution
+proc produceSyncCommitteeContribution*(slot: Slot,
+                                       subcommittee_index: SyncCommitteeIndex,
+                                       beacon_block_root: Eth2Digest): RestPlainResponse {.
+     rest, endpoint: "/eth/v1/validator/sync_committee_contribution",
+     meth: MethodGet.}
+  ## https://ethereum.github.io/beacon-APIs/#/Validator/produceSyncCommitteeContribution
 
-# proc publishContributionAndProofs*(body: seq[RestCommitteeSubscription]
-#                                   ): RestPlainResponse {.
-#      rest, endpoint: "/eth/v1/validator/contribution_and_proofs",
-#      meth: MethodPost.}
-#   ## https://ethereum.github.io/beacon-APIs/#/Validator/publishContributionAndProofs
+proc publishContributionAndProofs*(body: seq[RestSignedContributionAndProof]): RestPlainResponse {.
+     rest, endpoint: "/eth/v1/validator/contribution_and_proofs",
+     meth: MethodPost.}
+  ## https://ethereum.github.io/beacon-APIs/#/Validator/publishContributionAndProofs