diff --git a/apis/validator/aggregate_attestation.yaml b/apis/validator/aggregate_attestation.yaml
index c8aea024..76e6d713 100644
--- a/apis/validator/aggregate_attestation.yaml
+++ b/apis/validator/aggregate_attestation.yaml
@@ -1,7 +1,12 @@
 get:
   operationId: "getAggregatedAttestation"
   summary: "Get aggregated attestation"
-  description: "Aggregates all attestations matching given attestation data root and slot"
+  description: |
+    Aggregates all attestations matching given attestation data root and slot.
+
+    A 503 error must be returned if the block identified by the response
+    `beacon_block_root` is optimistic (i.e. the aggregated attestation attests
+    to a block that has not been fully verified by an execution engine).
   tags:
     - ValidatorRequiredApi
     - Validator
diff --git a/apis/validator/attestation_data.yaml b/apis/validator/attestation_data.yaml
index c7b8638e..65cfb94b 100644
--- a/apis/validator/attestation_data.yaml
+++ b/apis/validator/attestation_data.yaml
@@ -4,7 +4,12 @@ get:
     - Validator
   operationId: "produceAttestationData"
   summary: "Produce an attestation data"
-  description: "Requests that the beacon node produce an AttestationData."
+  description: |
+    Requests that the beacon node produce an AttestationData.
+
+    A 503 error must be returned if the block identified by the response
+    `beacon_block_root` is optimistic (i.e. the attestation attests to a block
+    that has not been fully verified by an execution engine).
   parameters:
     - name: slot
       in: query
diff --git a/apis/validator/sync_committee_contribution.yaml b/apis/validator/sync_committee_contribution.yaml
index 37809791..791d0db3 100644
--- a/apis/validator/sync_committee_contribution.yaml
+++ b/apis/validator/sync_committee_contribution.yaml
@@ -4,7 +4,12 @@ get:
     - Validator
   operationId: "produceSyncCommitteeContribution"
   summary: "Produce a sync committee contribution"
-  description: "Requests that the beacon node produce a sync committee contribution."
+  description: |
+    Requests that the beacon node produce a sync committee contribution.
+
+    A 503 error must be returned if the block identified by the response
+    `beacon_block_root` is optimistic (i.e. the sync committee contribution
+    refers to a block that has not been fully verified by an execution engine).
   parameters:
     - name: slot
       in: query