# Optimism Upgrade 20 Replaces Output Roots With Multi-Chain Super Root

By Simon Yoon

Canonical URL: https://www.tokenpost.com/news/technology/24565
Published: 2026-09-27T08:13:20.000Z
Updated: 2026-09-27T08:13:20.000Z
Section: Technology

> The OP Stack update preserves existing withdrawal proofs while preparing its fault-proof system for future cross-chain messaging.

Optimism released Upgrade 20 on Sept. 25, replacing the OP Stack’s single-chain output root with a multi-chain super root to prepare its fault-proof system for cross-chain interoperability.

The super root combines a version byte, timestamp and multiple chain ID-output root pairs into a single hash. That structure can represent the state of multiple chains at the same point in time.

Dispute processes will continue to operate separately for each chain. The upgraded system is designed to account for dependencies between chains while preserving the independent handling of fault-proof disputes.

The rollout is incremental to reduce implementation risk. Withdrawal proofs will continue to use output roots, allowing existing withdrawal logic to remain compatible with the upgrade.

Node operators do not need to take action. Chain operators must update their configurations to support Upgrade 20.

A later hard fork will formally enable cross-chain message passing across the OP Stack. The ecosystem secured about $17 billion across OP Stack chains as of Aug. 31, 2026, extending Optimism’s infrastructure beyond OP Mainnet. That figure measures value secured across OP Stack networks, a metric distinct from decentralized-finance total value locked, which tracks assets deposited in protocols and applications. TokenPost previously reported on the OP Stack ecosystem’s secured value.

## Links in this article

- [reported on the OP Stack ecosystem’s secured value](https://www.tokenpost.com/news/technology/23697)