Fault proofs have been implemented into Optimism smart contracts. Additional OP Stack Chains - including the likes of Base, Metal, Mode, and Zora -  are expected to upgrade soon to include this functionality.

The team announced,

“Open source, permissionless fault proofs are live on OP Mainnet, and with them the OP Stack arrives at Stage 1 decentralization. This is a major step forward for the Superchain!”

On the Ethereum L2 network, users can now initiate withdrawals of ETH and ERC-20 tokens from the mainnet sans the involvement of any trusted third parties.

Retrospectively, invalid withdrawals by sequencers can be challenged and removed by any user who submits a fault proof depicting that the withdrawal is invalid.

Fault proofs can be invalidated by the Optimism Security Council, provided it secures a six-of-eight vote. Further elaborating on this, the blog post clarified,

“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.”

According to Vitalik Buterin’s list of milestones, Optimism has now reached “Stage 1” of decentralization.

The Ethereum co-founder has time and again asserted that users should accept some L2 centralization right off the bat, but developers ought to fully decentralize ecosystems with time.

According to the Optimism team, the fault proof system lays the groundwork for achieving “multi-proof nirvana.” The endgame is Stage 2 decentralization. They asserted,

"Looking ahead, we must progress beyond Stage 1. Working towards Stage 2 is the next step.”

In the coming months, the team is looking to roll out additional proof systems - including Asterisc and Kona - on the testnet.