diff --git a/CHANGES.md b/CHANGES.md
index 6f6570ec..d13be711 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -40,7 +40,7 @@ There are likely to be descriptions etc outside of the list below, but new query
 | [#608](https://github.com/ethereum/beacon-APIs/pull/608) `POST /eth/v1/validator/prepare_beacon_proposer` deprecated         |                                                  |                                                  |                                                    |                                                 |                                           |
 | [#608](https://github.com/ethereum/beacon-APIs/pull/608) `POST /eth/v1/validator/register_validator` deprecated         |                                                  |                                                  |                                                    |                                                 |                                           |
 | [#608](https://github.com/ethereum/beacon-APIs/pull/608) `POST /eth/v1/validator/beacon_committee_subscriptions` updated         |                                                  |                                                  |                                                    |                                                 |                                           |
-| [#621](https://github.com/ethereum/beacon-APIs/pull/621) `payload_attributes EVENT` updated         |                                                  |                                                  |                                                    |                                                 |                                           |
+| [#621](https://github.com/ethereum/beacon-APIs/pull/621) / [#638](https://github.com/ethereum/beacon-APIs/pull/638) `payload_attributes EVENT` updated         |                                                  |                                                  |                                                    |                                                 |                                           |
 | [#651](https://github.com/ethereum/beacon-APIs/pull/651) `GET /eth/v1/beacon/blinded_blocks/{block_id}` deprecated         |                                                  |                                                  |                                                    |                                                 |                                           |
 | [#651](https://github.com/ethereum/beacon-APIs/pull/651) `POST /eth/v2/beacon/blinded_blocks` deprecated         |                                                  |                                                  |                                                    |                                                 |                                           |
 | [#651](https://github.com/ethereum/beacon-APIs/pull/651) `GET /eth/v3/validator/blocks/{slot}` deprecated         |                                                  |                                                  |                                                    |                                                 |                                           |
diff --git a/apis/eventstream/index.yaml b/apis/eventstream/index.yaml
index 0ead32ca..cd0e2002 100644
--- a/apis/eventstream/index.yaml
+++ b/apis/eventstream/index.yaml
@@ -144,6 +144,9 @@ get:
                 - `parent_block_root`: the beacon block root of the parent block to be built upon.
                 - `parent_block_number`: the execution block number of the parent block. Removed from `gloas` onwards.
                 - `parent_block_hash`: the execution block hash of the parent block.
+                - `safe_block_hash`, `finalized_block_hash`: the execution block hashes the node would pass
+                   as `safeBlockHash` and `finalizedBlockHash` in `engine_forkchoiceUpdated` when building
+                   on `parent_block_hash`. Added from `gloas` onwards.
                 - `proposer_index`: the validator index of the proposer at `proposal_slot` on
                    the chain identified by `parent_block_root`.
                 - `payload_attributes`: beacon API encoding of `PayloadAttributesV<N>` as
@@ -159,7 +162,7 @@ get:
                 ignored by block builders and most other API consumers.
               value: |
                 event: payload_attributes
-                data: {"version": "gloas", "data": {"proposer_index": "123", "proposal_slot": "10", "parent_block_root": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "parent_block_hash": "0x9a2fefd2fdb57f74993c7780ea5b9030d2897b615b89f808011ca5aebed54eaf", "payload_attributes": {"timestamp": "123456", "prev_randao": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "suggested_fee_recipient": "0x0000000000000000000000000000000000000000", "withdrawals": [{"index": "5", "validator_index": "10", "address": "0x0000000000000000000000000000000000000000", "amount": "15640"}], "parent_beacon_block_root": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "slot_number": "10", "target_gas_limit": "60000000"}}}
+                data: {"version": "gloas", "data": {"proposer_index": "123", "proposal_slot": "10", "parent_block_root": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "parent_block_hash": "0x9a2fefd2fdb57f74993c7780ea5b9030d2897b615b89f808011ca5aebed54eaf", "safe_block_hash": "0x9a2fefd2fdb57f74993c7780ea5b9030d2897b615b89f808011ca5aebed54eaf", "finalized_block_hash": "0x9a2fefd2fdb57f74993c7780ea5b9030d2897b615b89f808011ca5aebed54eaf", "payload_attributes": {"timestamp": "123456", "prev_randao": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "suggested_fee_recipient": "0x0000000000000000000000000000000000000000", "withdrawals": [{"index": "5", "validator_index": "10", "address": "0x0000000000000000000000000000000000000000", "amount": "15640"}], "parent_beacon_block_root": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "slot_number": "10", "target_gas_limit": "60000000"}}}
             data_column_sidecar:
               description: The node has received a DataColumnSidecar (from P2P or API) that passes all gossip validations on the data_column_sidecar_{subnet_id} topic
               value: |