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…eflect optionality removal Removes `Optional[T]` mapping as it is replaced by specific zero/empty value encoding in container definitions. Updates `PayloadStatusV1`, `ForkchoiceUpdatedResponseV1`, `ExecutionPayloadBodyV1`, and `ExecutionPayloadBodyV2` to use non-optional types where JSON mapping implies a zero/empty value instead of true optionality. Updates SSZ mappings for `engine_getPayloadBodiesByHashV1/V2` and `engine_getBlobsV1/V2/V3` to use nested lists (`List[List[T, 1]]`) instead of `Optional[T]` to represent the presence or absence of data, consistent with non-null SSZ encoding for absent data. Adds notes explaining the zero/empty encoding for absent fields.
…update examples The documentation for how `T or null` maps to SSZ encoding is being clarified. Replaced the generic statement about `Optional[T]` being encoded as `List[T, 1]` with a more direct explanation that it is represented as `List[T, 1]`. Also updated the description for `payload_attributes` in `ForkchoiceUpdated` requests to explicitly state that presence is indicated by a list with 1 element, matching the SSZ type definition. Additionally, added missing vocabulary words to `wordlist.txt` to improve future documentation generation tools.
…ation to reflect capability exchange The transport negotiation mechanism has been updated to exclusively use `engine_exchangeCapabilities` over JSON-RPC for determining support of SSZ REST endpoints. This change clarifies the required steps for clients to discover and utilize the binary SSZ transport.
Update documentation to better explain how JSON-RPC remains the default for negotiation and fallback, explicitly stating when binary SSZ is used. This clarifies the steps involved for CL and EL during initialization.
shemnon
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Mar 5, 2026
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| - The CL uses SSZ natively, forcing a round-trip conversion (SSZ to JSON, then JSON to internal types) at the Engine API boundary. | ||
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| Binary SSZ eliminates all of this. The CL sends raw SSZ bytes over HTTP; the EL deserializes directly. No hex encoding, no JSON parsing, no intermediate representations. Payload sizes are reduced by 50% or more compared to JSON-RPC, and serialization is no longer a bottleneck in the critical path between CL and EL. |
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The EL uses RLP, why not RLP? The EL does not currently support SSZ while the CL does support RLP for various reasons. This would reduce the number of libraries in the EL but be net zero for the CL.
What unique utility does SSZ provide?
This was referenced Mar 8, 2026
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Core change: Full binary SSZ over REST. No JSON, no hex encoding - raw SSZ bytes over HTTP.
Rationale: