Bitcoin OP_RETURN as a Cross-Chain Signal
tactic
Core idea
On Bitcoin, an OP_RETURN output carries arbitrary data and plays a role similar to input data on EVM: bridges and services sometimes use it to embed routing or reference information. Seeing an OP_RETURN next to a transfer is a clue that a service is involved, and it can point you to the next hop.
When to use
When a Bitcoin transaction you are tracing contains an OP_RETURN output, or when you suspect a bridge or service is in play but cannot see an explorer link.
Components
- Spot it: an OP_RETURN shows up as a data output, usually near-zero value, among the normal outputs.
- Identify the service by counterparty, not just by the code: put the Bitcoin address into an attribution tool such as Arkham and read its top counterparties. A large share of value flowing to a known service address (for example RelayLink) attributes the address and tells you which bridge or service to consult.
- Decode the data if useful: OP_RETURN decoder sites can expose the raw message (which may look like a reference or a hash), but they often leave further work to do and some are low-trust, so corroborate anything you pull from them.
- Resume via the right explorer: once the service is identified, use its own explorer (search the address or the reference) to find the destination leg.
Example
A Bitcoin transaction shows an OP_RETURN plus two small outputs. Arkham attributes the receiving address to RelayLink by its counterparties; searching that address on relay.link then reveals the two deposits paying out as USDC on Polygon.
Related
Non-Explorer Bridge Correlation, Time-and-Value Analysis, Decoding a Cross-Chain Destination Address from Input Data, Cross-Chain Obfuscation Categories