Interop is currently in active development and not yet ready for production use. The information provided here may change frequently. We recommend checking back regularly for the most up-to-date information.

OP-Supervisor

OP-Supervisor is a service that verifies cross-chain messages and manages interoperability between chains in the OP Stack. The main information it contains about other blockchains is:

Log entries, which could be initiating messages for cross-domain messages.
Blockchain heads, which are the latest blocks at various levels of confidence and safety:
- Unsafe (the latest block available through the gossip protocol)
- Local-safe (the latest block written to L1)
- Cross-safe (the latest block written to L1, and for which all the dependencies are written to L1)
- Finalized (the latest block written to L1, and that L1 block is safe from reorgs)

To do this, OP-Supervisor has to have RPC access to all the chains in the dependency set (all those that can contain an initiating message whose destination is this blockchain).

How other components use OP-Supervisor

The execution client (typically op-geth) queries op-supervisor during block-building to verify if a message is sufficiently safe to include. To do this, the execution client looks at every executing message and queries op-supervisor to see if there is a corresponding initiating message.
op-node queries cross-chain safety information and coordinates safety updates between OP stack nodes and op-supervisor. It uses the API provided by op-supervisor to:
- Retrieve the unsafe, local-safe, cross-safe, and finalized heads for other chains.
- Update the unsafe, local-safe, and finalized heads for its own chain.
- Attempt to promote blocks in its own chain to cross-safe status.
- Attempt to finalize L2 blocks based on L1 finality.

API

Here are the most important API methods exposed by OP-Supervisor. For a full listing of API names, see the source code (opens in a new tab).

Method(s)	Description
`UnsafeView` and `SafeView`	Return the Local and Cross heads for their respective levels
`DerivedFrom`	OP Nodes use to check the L1 source of the Supervisor (needed for Safe Head tracking)
`UpdateLocalSafe` and `UpdateLocalUnsafe`	Tell the Supervisor when the Node's heads change
`Finalized`	Returns the Finalized Head
`UpdateFinalizedL1`	Signals to the Supervisor new finality signals
`CheckMessage`	Checks logs in the DB directly in tests

Next steps

Build a revolutionary app that uses multiple blockchains within the Superchain
Deploy a SuperchainERC20 to the Superchain
Practice how to use Superchain interop message passing
Learn about manually relaying messages
Learn how ETH can move across chains (opens in a new tab)
Want to learn more? Read our guide on the anatomy of a cross-chain message or check out this interop design video walk-thru (opens in a new tab)