EIP-8178 Binary SSZ Transport for the Engine API

DraftCorecreated 2026-03-01

Specifies a binary SSZ transport as an alternative to JSON-RPC for Engine API communication

Author: Giulio Rebuffo (@Giulio2002)

What the specification covers

Abstract Motivation Specification Transport Base URL Content Types Authentication Versioning HTTP Status Codes Success Client Errors Server Errors Constants SSZ Type Mappings Container Definitions WithdrawalV1 ExecutionPayloadV1 ExecutionPayloadV2 ExecutionPayloadV3 PayloadStatusV1 ForkchoiceStateV1 PayloadAttributesV1 PayloadAttributesV2 PayloadAttributesV3 ForkchoiceUpdatedResponseV1 ExecutionPayloadBodyV1 BlobsBundleV1 BlobsBundleV2 BlobAndProofV1 BlobAndProofV2 TransitionConfigurationV1 GetPayloadResponseV2 GetPayloadResponseV3 GetPayloadResponseV4 GetPayloadResponseV5 PayloadBodiesV1Response GetBlobsV1Response GetBlobsV2Response GetBlobsV3Response ClientVersionV1 GetClientVersionV1Response Endpoints Payloads POST /engine/v{N}/payloads — Submit execution payload GET /engine/v{N}/payloads/{payload_id} — Retrieve built payload POST /engine/v{N}/payloads/bodies/by-hash — Get payload bodies by hash POST /engine/v{N}/payloads/bodies/by-range — Get payload bodies by range Forkchoice POST /engine/v{N}/forkchoice — Update fork choice Blobs POST /engine/v{N}/blobs — Get blobs by versioned hash Client POST /engine/v1/client/version — Exchange client version Endpoint Summary Example Submit payload Retrieve built payload Update fork choice Rationale Why REST instead of raw SSZ over TCP?Why same port instead of a separate port?Why application/octet-stream?Why text/plain for errors instead of JSON?No hard fork required Backwards Compatibility Security Considerations Copyright

This proposal declares no Solidity interface, so there is nothing to compute. It may be a core protocol change, a meta proposal, or written in prose only.

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