Adding ZK to @Arbitrum BoLD protocol was surprisingly simple. How does it work? Today, BoLD settlement works like this: → Proposers can make assertions (a claim about the chain's new state); when a new assertion comes in a challenge timer starts → No rival assertion within the challenge window? The assertion is confirmed → Rival posted? The challenge protocol kicks in New multi-prover path (everything above still holds, plus): → A proposer can prove any unconfirmed assertion with a ZK proof + K-of-N attestations from the Fast Confirmation Committee → ZK proof verifies on the parent chain & enough attestations check out? The assertion settles early - no waiting out the challenge window Why this beats a ZK-only design: 1. Multi-prover security: Fast confirmation needs two independent systems to agree: a ZK proof verified on the parent chain + attestations from committee nodes re-executing the chain. To fast-confirm a bad state, an attacker has to break both at once. TEE-run committee nodes are planned as a further hardening step. 2. Deterministic upper bound on settlement: If the prover stalls or has a bug, the chain simply falls back to optimistic settlement: slower, never halted, funds untouched. A ZK-only chain in the same spot may never settle without security council action. 3. Pay for proving only when you need it: Proving is optional per assertion: pure fraud-proof chains pay nothing, Hybrid ZK chains proves on demand to settle early or resolve disputes, and ZK Prove All chains prove everything for always-fast settlement. ZK-only stacks have one mode: prove every batch, forever. @Offchain will bring a proposal to the DAO to upgrade Arbitrum One to ZK settlement, and other chains built with Arbitrum Platform will be able to upgrade at will. Stay tuned for more 👀