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devcon8 / light client backfill in prysm

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Light Client Backfill in Prysm

Duration: NaN:NaN:NaN

Speaker: Fuchuan Jeff Chung

Type: CLS - EPF Talk

Expertise: No prior knowledge

Event: Devcon

Date: Nov 2026

Most beacon nodes today checkpoint-sync, meaning they never process historical states and cannot serve old-period light client data. As adoption grows, supply of historical LC updates decays — threatening bridges and mobile wallets that need to sync from old trusted roots. I will be presenting how a backfill protocol is designed and implemented in Prysm as part of EPF Cohort 7. The protocol downloads per-period anchor proofs, exhaustively verifies block coverage to prevent omission attacks, locally re-runs is_better_update to determine canonical best updates, and reconstructs bootstraps — all anchored to already-trusted data via Merkle proofs. Each backfilled period turns the node into a supplier, reversing the supply decay.

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ConsensusDecentralization