# L2 Interop Working Group - Call #15 **Oct 1, 2025** - [Recording](https://youtu.be/ySiKDAdyVMw) - [Calendar invite for future calls](https://docs.google.com/forms/d/e/1FAIpQLSfMFEJmyVgjLuiipgxprEkiQXwwK3F_PfGbWvU8ZmV6e_ka0A/viewform) ### [Agenda](https://github.com/ethereum/pm/issues/1741) 1. Fast Synchronous Finality (FSF) [EF Protocol Consensus team] 1. ENS-based chain registry [Unruggable + Wonderland] 1. Sync Composability UX [ssv.network] 1. L2 withdrawal windows / reducing 7 day challenge periods ## Call Notes *condensed notes below – watch the recording (above) for full discussion* --- ### 1. [Fast Synchronous Finality](https://docs.google.com/presentation/d/1kbl-yvLNaplca_PUecfUOO_KAI-SRyeVEMpx8JsHemw/edit?usp=sharing) (FSF) Development Update - Finality rule providing single slot finality under synchronous network conditions - [slides here](https://docs.google.com/presentation/d/1kbl-yvLNaplca_PUecfUOO_KAI-SRyeVEMpx8JsHemw/edit?usp=sharing) - 98.75% improvement over economic finality (12 seconds vs 16 minutes) - Accepts lower adversarial threshold (20-25% vs 33%) - No economic security guarantees (vs 33% stake requirement) - Requires synchronous network - Performance measurements show strong results: - 95% of blocks finalized in <20 seconds - 99% finalized in <2 slots - 100% finalized in 7-8 slots - Long tail performance issues due to late blocks/empty slots being addressed #### Technical Implementation & Trust Assumptions - Algorithm analyzes attestations with strong conditions to ensure canonical chain inclusion - Assumes maximum fraction β (20-25%, configurable) of committee stake is dishonest - Works by checking block support against threshold including adversarial weight considerations - Concerns about assumption strength vs economic finality - FSF doesn’t replace full finality for high-security use cases - Stronger than current block confirmation patterns for many applications - Highlighted need for L1 origin verification for L2 interop protocols #### Development Status & Next Steps - Current state: - Draft specifications and proof of correctness complete - Proof-of-concept in Teku and Lighthouse tracking latest spec - Proof-of-concept in Prysm implementing partial specs - Working on empty slot case improvements - Next priorities: - Finalize specifications and proofs - Write spec tests - Get more real-life measurements - Move proofs-of-concept to production - Implement FSF in any client - No hard fork required - algorithm applies by analyzing existing attestations - Ellie to help lead work on FSF at EF, will reach out for feedback ### 2. ENS-Based Chain Registry & Synchronous Composability - Unruggable/Wonderland presenting ENS resolver for chain name to ERC-7930 identifier resolution - Three contracts: chain registry (source of truth), chain resolver, reverse resolver - Migration script from GitHub to onchain registry - Multisig governance initially, ownership model to be refined ### 3. SSV Network introduced “Compose” project for sync composability - Latest work from ssv.network called Compose: shared publisher for synchronous crosschain composability - Uses shared publisher with independent sequencers vs shared sequencer model - see https://www.compose.network/shared-publisher - and https://github.com/compose-network - Custom RPC calls for cross-chain transaction coordination - Trust assumptions: shared publisher based on Ethereum validators, produces ZK proofs ### 4. L2 withdrawal windows discussion flagged for reducing 7-day challenge period to 1 day - Exploring secure designs while maintaining strong censorship protection - See old [ethresearch post](https://ethresear.ch/t/optimistic-rollups-the-challenge-period-and-strong-censorship-attacks/21721) from Donnoh (l2beat) for more context