Proof System

X Layer has launched its Hybrid Proof system, combining optimistic proposal with on-demand ZK proving to substantially improve L2 security without sacrificing block production efficiency. Under normal operation, the Proposer submits Output Roots optimistically with no proof generation. When a Challenger disputes a proposal, the system enters a proving window during which the Proposer self-attests via the SP1 zkVM. Compared to interactive Fault Proofs that require many rounds of on-chain bisection, Hybrid Proof reduces dispute resolution to a single ZK verification, sharply cutting both Gas cost and time-to-resolution. The upgrade went live on X Layer testnet on May 6, 2026, shortening the challenge period from the OP Stack default of 7 days to 1 day.This article walks through the design rationale, mechanism, and engineering choices behind X Layer's Hybrid Proof, and examines its impact on developers and users.