Optimism Upgrade 20 Approved for Mainnet Implementation on September 24

Optimism (OP) governance has approved Upgrade 20. The new fault proof system will undergo at least seven days of validation across four testnets before being applied to the mainnet on September 24, provided no issues arise. Optimism governance concluded voting on September 16. The Optimism Governance Forum set September 24 as the target date for mainnet execution.

The new system will first be implemented on OP Sepolia, Ink Sepolia, Sonium Minato, and Unichain Sepolia. The conditional schedule requires stability confirmation over a minimum of seven days on testnets. The key change involves shifting from the existing 'output root dispute game' to the 'super root dispute game' for fault proof verification.

Fault proof verifies whether Layer 2 states are correct before withdrawals are finalized on Ethereum (ETH) mainnet, acting as a security measure. Previously, validation was based on Layer 2 block numbers; after the upgrade, timestamps will be used instead. This change allows multiple OP Stack chains to verify states at the same time, enabling a more unified structure for managing states across several Layer 2 networks.

The Optimism-driven superchain aims to connect various Layer 2 networks using OP Stack into one ecosystem for cross-chain asset and data movement. However, Upgrade 20 does not immediately activate this functionality. Instead, it prepares the security infrastructure for future interoperability by updating fault proof systems before introducing cross-chain features.

CryptoSlate reported that after the upgrade, dispute infrastructures will remain separate per chain, with individual chains' output roots included in the super root dispute game. This means the new system does not simply consolidate multiple chains into one game but adjusts verification processes for future scalability. Chain operators must update relevant software: 'op-proposer' will use super root RPC and the new game type, while 'op-challenger' and 'op-dispute-mon' require super root RPC settings. Permissioned chains will use game type 5, and non-permissioned chains game type 9.

Legacy configurations will coexist for a period to complete existing validation processes. General users do not need to take action; withdrawal proofs submitted before the upgrade remain valid. The Optimism Portal supports both old output root formats and new dispute game types. There are no separate Layer 2 hard forks or node activation timelines, but chain operators must verify testnet validation and adjust software settings.

Upgrade 20 will deploy the new fault proof system on four testnets before a cooling period to identify errors and stability issues. If no problems arise during testing, the contract upgrade will be executed on OP, Ink, Sonium, and Unichain mainnets on September 24, subject to testnet validation results.