Post-Quantum (PQ) Interop #28, February 25, 2026

[will-corcoran]

UTC Date & Time

February 25, 2026, 14:00 UTC

Agenda

Resources

• Facilitator email: will@ethereum.org
• Facilitator Telegram: @corcoranwill
• Telegram: PQ Interop — threads: #general, #devnet-1, #devnet-2, #devnet-3, #tooling, #leanVM, #onboarding

High-Level Documents

• Devnet-0 : lean consensus client interop
• Devnet-1 : PQ signature signing & verification
• Devnet-2 : single-layer PQ signature aggregation
• Devnet-3 : aggregator role separation + subnet aggregation

A. Devnet-3: Implementation Status

Client Readiness

Client	Implementation	Spec Tests	Interop	Docker	Notes
Zeam	✅	✅	⏳	✅	Ready to interop, waiting for other clients. Working on checkpoint sync issues. leanQuickStart ready for Devnet-3.
Ream	✅	🔶	⏳	🔶	Spec fully implemented. Self-finalization tests not passing yet (debugging). Docker image ready for testing imminently.
Qlean	🔶	⏳	⏳	⏳	Kamil traveling (AFK this call).
Lantern	✅	✅	⏳	✅	All specs implemented, tests passing. Local 4-node test showed justification/finalization. Ready to release Devnet-3 image for interop.
Ethlambda	🔶	🔶	⏳	⏳	Internal 4-node Devnet running. Testing Devnet-3 implementation. Added checkpoint sync + chain guidance support. Next: code review/polish for Devnet-3 branch.
Lighthouse	⏳	⏳	⏳	⏳	Back after ~1 month. Starting to target Devnet-3. Will take more time.
Grandine	🔶	⏳	⏳	⏳	Multiple Devnet-2 fixes landed, more stable now. Still significant work remaining for Devnet-3.
Nimbus	❓	❓	❓	❓	No representative on call.

Legend: ✅ Complete | 🔶 In progress | ⏳ Not started | ❓ Unknown

Devnet-3 Interop Status

• Zeam + Lantern: Both ready to begin interop testing
• Ream: Docker image expected within days; debugging self-finalization
• Ethlambda: Internal testing in progress, polish phase next

B. Devnet-4: Specification Status

🎉 Recursive Aggregation API Complete (Emil)

• Finished: Recursive aggregation implementation ready
• API approach: Simplified — no Merkle tree of pubkeys needed
  • When verifying aggregated signature, simply feed the list of public keys directly
  • Most efficient approach after testing alternatives
• Link: Test with API shared in Telegram (leanVM channel)
• Next: Working on optimizations

Spec Discussion: SSZ Signature Container

Issue raised (Unnawut): leanSpec serializes signatures as variable-size lists (path/hashes), but all clients implement fixed-size bytes.

Discussion:

• Lantern implemented variable-size per spec but added fixed-size fallback
• Fixed-size is cheaper and matches all client implementations
• Root cause: Variable-size was likely an early spec choice that doesn't reflect the constant dimensions

Resolution: Thomas to update spec to use fixed-size (vector instead of list). Unnawut reverting Ream back to fixed-size.

Research Updates

• leanSpec minimal client (Thomas): Interop tests passing locally (self-interop). Sync still flaky, but networking and fork choice stable.
• Specification book (Thomas): Added 3SF-mini section, to be published soon.
• Pubkey PQ registry (Thomas): Starting to draft a post on post-quantum public key registry.
• Beacon spec modernization: Discussions ongoing about merging with leanSpec.

C. Long-Running Devnet-2 & Checkpoint Sync

Devnet-2 Stability

• 🎉 24+ hours finalized: Long-running Devnet-2 reached almost 24 hours of continuous finalization
• Ream: Reached 13,000 slots; fixed log size issues
• Grandine: Multiple stability fixes landed

Checkpoint Sync Testing (Katya)

• Found working combination for 4 clients
• Testing order: Zeam → Ethlambda → Lantern
• Lantern implementing checkpoint sync flag for Devnet-2 image (serving finalized/justified states)

Devnet-2 Bug Fixes

Client	Fix
Lantern	QUIC certificate rotation when expired
Ethlambda	Reduced memory during long syncs (upload pending blocks to disk); improved checkpoint sync; added chain guidance support; wrote checkpoint sync + consensus documentation

D. New Client Onboarding

Client	Target Devnet	Implementation	Spec Tests	Interop	Docker	Notes
Gean	Devnet-1 → 2	✅	✅	⏳	🔶	Integrated leanSig (block/attestation signing, signature verification). Integrated leanMetrics for Devnet-1. PR for leanQuickStart expected tomorrow for multi-client interop. Then targeting Devnet-2.

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PQ Interop

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