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Add experimental builder bid streaming - #10418
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After Gloas, the beacon node asks each direct builder for a bid with
getExecutionPayloadBid at block production. With the experimental
--builder-bid-streaming flag (off by default) it can instead open a
websocket bid stream to each builder just before its slot:
GET /eth/v1/builder/execution_payload_bid_stream/{slot}/{parent_hash}/
{parent_root}/{proposer_pubkey}, one [0x01][fork byte][SSZ
SignedExecutionPayloadBid] message per bid.
The beacon node keeps the builder_preferences entries the validator
client posts, and once it knows the parent for its next slot it prepares
a stream per entry. Each stream connects a second before the slot, with
Date-Milliseconds and X-Timeout-Ms giving slot start as the deadline, the
same way an HTTP bid request gives its deadline, so builders send their
bid just before it. The latest bid is kept until block production.
At block production each builder's bid comes from its stream or from
HTTP, and goes through the same validation as an HTTP bid:
- A stream with a bid gives that bid. If it fails to decode or validate,
request over HTTP.
- A stream that connected but got no bid means no bid.
- With no stream, a stream that never connected, or one opened for a
different parent or auth, request over HTTP as before.
The proposal's streams are then closed, and they are also closed when
block production skips direct bids. A bid's signature is only decoded at
block production, on the blocking pool. Each stream has limits on message
size, message count and bytes read, a proposal streams from at most 64
builders, and a stream doesn't connect with less than 500ms left. Streams
trust the same roots as the HTTP client.
- Do all bid stream timing on the slot clock instead of Instant::now. - Read the proposer pubkey for bid streams from the head state, so proposer prep doesn't lock the pubkey cache. - Call the time block production takes the bids the auction end. - Try a builder that answered 404 or 405 again at its next proposal, instead of using HTTP for it until restart.
jimmygchen
marked this pull request as ready for review
October 22, 2026 02:55
eserilev
approved these changes
Oct 22, 2026
eserilev
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Couldn't find any issues, LGTM!
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Issue Addressed
From Gloas, the beacon node requests each direct builder's bid with
getExecutionPayloadBidat block production, and waits up to 400ms for responses. With bid streaming, it connects to each builder shortly before the slot, and builders can keep sending better bids, each replacing the last. At block production we use each builder's latest bid.Proposed Changes
Bid streaming is experimental and off by default (
--builder-bid-streaming). Onceprepare_beacon_proposerknows the next slot's parent, the beacon node opens a websocket to each builder in the VC'sbuilder_preferencesa second before the slot:Each message is
[0x01][fork byte][SSZ SignedExecutionPayloadBid]. As with HTTP bid requests,Date-MillisecondsandX-Timeout-Msset slot start as the deadline, so the proposer decides when bidding closes.Additional Info