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OP Stack interop is in active development. Some features may be experimental.
OP Stack interoperability is a set of protocols that lets OP Stack chains read each other’s state, so a network of chains can feel like a single blockchain: ETH and ERC-20 tokens move between chains by native minting and burning, and contracts can compose with events from other chains at low latency. Interop is in active development and is being rolled out iteratively, so read these materials as a picture of where the stack is going and what you can already build against, not as a finished production system. Start with the short introduction, then work through the mechanism pages in order: they build from the message-passing model up to reorg safety and the runtime that enforces it. The tutorials let you try everything on local or devnet chains, and the spec is the normative definition throughout.

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Start here

  • OP Stack Interoperability: read this first for what interop enables (native asset transfers, cross-chain composability, horizontal scalability) and where to start building.

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Go deeper

  • OP Stack interoperability explainer: the architecture end to end, covering initiating and executing messages, access-list validation, block safety levels, and dependency sets and clusters.
  • Interop message passing overview: the messaging lifecycle at contract level, from the low-level CrossL2Inbox to the L2ToL2CrossDomainMessenger most apps use.
  • Reading logs with OP Stack interop: the pull model, where a contract validates a log from another chain directly instead of receiving a message.
  • Message expiration: why an unrelayed message eventually expires and how to reemit one that did.
  • Superchain ETH Bridge: how native ETH moves between chains through SuperchainETHBridge and the ETHLiquidity contract.
  • Interop reorg awareness: how interop delivers low-latency messages without opening the door to cross-chain double-spends.
  • OP Supernode: the runtime that hosts every chain in a dependency set in one process and performs the cross-chain verification work.

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Get hands-on

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The normative spec

The definitive definition of interop behavior lives in the OP Stack specifications:
  • Interop: the root of the interop specs and the map of everything below it.
  • Messaging: the normative definitions of initiating and executing messages and their safety rules.
  • Predeploys: the CrossL2Inbox, L2ToL2CrossDomainMessenger, and the other interop predeploy contracts.
  • SuperchainETHBridge: the specification of native ETH bridging between interop chains.

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Audits and security

  • Crosschain security measures: the trust model, what happens under sequencer equivocation, and the latency versus security tradeoff each chain configures.
  • Audit reports: the standing index of OP Stack security reviews, which routes to the full list in the monorepo.