Fast Confirmation Rule (FCR) Meeting #4, March 3, 2026

Ethereum Magicians

Agenda Bi-weekly, Tuesdays @ 14:00 UTC Facilitator: Will Corcoran ( will@ethereum.org · @corcoranwill ) YouTube Transcript Discord Spec PR Explainer Slides Prysm Write-up Client Implementation Status Client Status Contact Prysm Old algo impl; 25% on latest spec Terence Lighthouse EPF PoC; needs team review — Teku PoC complete; production dev starting Anton Nimbus Spec reviewed; active in spec PRs Etan Lodestar Spec tests passing; deploying to staking env Nazar Grandine TBD — Testing Format : Extended fork choice tests (Altair+) Status : Revert/restart tests merged; epoch boundary fix tests in progress Paper : Targeting mid-March Repo : [consensus-spec-tests TBD] Call 03 Summary (Feb 17, 2026) Headline Three spec PRs opened that directly reduce implementation complexity — a key theme from client dev feedback. Lodestar has all spec tests passing and is deploying to staking environments. We need more client teams engaged. Client Updates Lodestar (Nazar) : All spec tests passing after Mikhail fixed an attestation edge case. Next: fine-tune impl, add logging, deploy to staking environments for performance metrics. Nimbus (Etan) : Not on call but active in spec PR discussions — drove the FCR trigger timing proposal (see below). Teku / Prysm / Lighthouse / Grandine : No updates this call. Spec Changes — Reducing Implementation Complexity Three PRs opened against the spec branch. Client dev feedback on all three is welcome and needed. # PR What Status 1 #25 Epoch boundary checkpoint fix — FCR was consuming the updated checkpoint in the same slot it was written; fix defers the switch to the first slot of the current epoch Fix confirmed; tests updating this week 2 #26 Flexible FCR trigger timing — let clients call FCR after block arrival / attestation deadline instead of slot start, avoiding a redundant fork choice call Open for feedback; may leave unspecified so clients decide 3 #27 Use head state for FFG check — replace checkpoint state with head state in will_checkpoint_be_justified , since head state is always available in client implementations Open for feedback Additionally, Mikhail floated reusing fork choice weight/balance data instead of recomputing from state. Nazar confirmed this would significantly simplify Lodestar’s implementation. Worth exploring as a spec-level change. Exchange Integration / Engine API Exchanges get confirmation status via the EL safe block tag — FCR automatically populates this with the confirmed block . No exchange-side changes needed. In failure/revert cases, safe falls back silently to the finalized block. If FCR trigger timing moves within the slot, the rule must run before forkchoiceUpdated so the safe block propagates correctly. See related discussion . ePBS Sequencing Lodestar plan: merge ePBS fork choice changes first (~2 weeks), then layer FCR on top. FCR adds store fields but doesn’t change fork choice behavior — limited conflict surface, but worth monitoring. Testing & Research Test format adjusted per Call 02 feedback. Revert/restart tests merged. Next: update tests for epoch boundary fix ( #25 ); add coverage for new code paths. Paper targeting mid-March. Action Items Owner Item Nazar Deploy to staking env; report performance metrics Mikhail Update tests for #25 ; gather client feedback on #26 and #27 Luca Adjust tests for #25 ; continue paper work All client devs Review spec PRs #25 , #26 , #27 Will Async outreach to LH, Prysm, Grandine teams Agenda for Call 04 A. Client updates (round-robin) B. Spec PRs — #25 landed? Decisions on #26 and #27 ? C. Lodestar staking env metrics (Nazar) D. ePBS merge sequencing check-in E. Testing coverage update F. Open discussion Add agenda items : Comment below with topic Prior Calls Call Date Agenda / Minutes #01 Jan 20, 2026 ethereum/pm#1870 #02 Feb 3, 2026 ethereum/pm#1887 #03 Feb 17, 2026 ethereum/pm#1924 Meeting Time: Tuesday, March 03, 2026 at 14:00 UTC (60 minutes) GitHub Issue 1 post - 1 participant Read full topic