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Superchain interop is in active development. Some features may be experimental.
OP-Supervisor is a service that verifies cross-chain messages and manages interoperability between chains in the OP Stack. Anyone is able to run OP-Supervisor but only chain operators and full-node operators are expected to run OP-Supervisor. 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).

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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.

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API

Here are the most important API methods exposed by OP-Supervisor. For a full listing of API names, see the source code.
Method(s)Description
UnsafeView and SafeViewReturn the Local and Cross heads for their respective levels
DerivedFromOP Nodes use to check the L1 source of the Supervisor (needed for Safe Head tracking)
UpdateLocalSafe and UpdateLocalUnsafeTell the Supervisor when the Node’s heads change
FinalizedReturns the Finalized Head
UpdateFinalizedL1Signals to the Supervisor new finality signals
CheckMessageChecks logs in the DB directly in tests

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Next steps

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