Governance-approved, permissionless fault proofs are live on OP Mainnet, and with them the OP Stack arrives at Stage 1. This is a monumental milestone for the Superchain, and soon more OP Stack Chains will upgrade to include this functionality, starting with Base, Metal, Mode, and Zora.

The permissionless Fault Proof System enables withdrawals of ETH and ERC-20 tokens from OP Mainnet to be initiated without involvement from any trusted third parties. It also means that invalid withdrawals can be challenged and removed by any user that wants to participate in the protocol. While participation in the Fault Proof System is permissionless, the Optimism Security Council retains the power to intervene and revert the system back to a permissioned state in the event of a failure in the system. Having this fallback is part of a responsible and safe rollout of the Fault Proof System, and we believe the Security Council meets the well-formed, industry-standard definition of Stage 1 from L2Beat.

However, the OP Stack does not arrive at Stage 1 with the implementation of fault proofs alone. Additional safeguards explicitly targeted at the system ensure the Security Council can act swiftly and effectively in the event of a bug. In the event that safeguards are activated, withdrawals will be reset, necessitating the reproving of all pending withdrawals. Security is the first consideration for everything built into the OP Stack, and these efforts, in conjunction with the fault proofs work, bring the OP Stack to Stage 1 capabilities.

In 2022, Vitalik outlined a framework for how L2s could slowly remove their training wheels and move towards full decentralization. It’s common for L2 projects to launch early, at various stages of development, and kickstart  an ecosystem before the security model is fully permissionless. As projects progress, they can take off their training wheels and advance from Stage 0, to Stage 1, to eventually Stage 2 decentralization.

Now that we’re confident in the Stage 1 security model, and the Security Council’s ability to keep the system secure in all events has been thoroughly reviewed by core dev teams and some of the ecosystem’s most respected and diligent security auditors, working towards Stage 2 is the next step. Next up: the audit of the Dispute Game itself, taking place in July.

But looking ahead, we must progress beyond Stage 1.

L2s launch at various stages of development, and it’s common for these projects to build their ecosystem and strengthen their code in tandem. As projects mature, so does their code, and their progress towards decentralization also evolves. The safety measures or “training wheels” that were in place in the early stages are no longer necessary.

Launching fault proofs on OP Mainnet, extending the functionality to other OP Stack Chains in the Superchain ecosystem, and achieving Stage 1 decentralization are important milestones – but the endgame is Stage 2 decentralization.

Today’s Fault Proof System lays the groundwork for achieving “multi-proof nirvana” – like the OP Stack itself, it is open-source and modular by design. This framework aims to enable the OP Stack to support multiple proof systems, including zero knowledge proofs, alongside the current system, Cannon. Productionizing redundant proving schemes to secure withdrawals from OP Stack Chains back to Ethereum enables limiting the Security Council's role to only choosing between proofs in the event that they disagree.

The Fault Proof System was built and tested by core development teams from across the Superchain, like OP Labs, Base, and Sunnyside Labs. This collaborative approach has made this launch possible. The fault proof proposal was also approved by Optimism's Token House and Citizens' House, passing Optimism governance's two-step approval process.

In the coming months, we seek to roll out additional proof systems, including Asterisc and Kona, on testnet. Proving out the reliability and robustness of these redundant proof schemes will help the Superchain reach Stage 2 decentralization.

We’re celebrating the launch of fault proofs, and the OP Stack’s arrival at Stage 1, and feeling optimistic about the Superchain’s path towards realizing a fully decentralized future.