ANYPREVOUT
A proposed SIGHASH flag (BIP-118) enabling partially signed transactions without strictly binding to specific inputs, unlocking advanced Layer-2 protocols.
ANYPREVOUT (specifically SIGHASH_ANYPREVOUT and its variant SIGHASH_ANYPREVOUTANYSCRIPT) is a proposed Bitcoin Script signature-hashing mode that would let a signed transaction be applied against any matching prior output rather than committing to one specific input. Specified in BIP-118, it's the key cryptographic primitive needed for Eltoo-style channels and various advanced protocols.
The technical change in plain terms:
- Today, when you sign a Bitcoin transaction, the signature commits to specific input txids - "I'm signing a transaction that spends UTXO X." If those input UTXOs change for any reason (e.g., a different transaction emerges that spends them under different terms), your signature is invalid.
- With ANYPREVOUT, you can sign in a way that says "I'm signing a transaction that would spend whichever UTXO matches a certain script template." If the actual input is changed before broadcast, the signature still applies as long as the script template matches.
What this enables:
- Eltoo channels. The proposed simpler alternative to current Lightning channel design. Every new channel state is signed in a way that lets it apply against any prior commitment, replacing the punishment-based mechanism with a simpler "newer states override older states" model.
- Lightning Network protocol cleanups. Various advanced Lightning constructions (multi-party channels, channel factories, simplified routing) become more practical.
- Simpler vault designs. Some vault constructions become easier with ANYPREVOUT.
ANYPREVOUT has been proposed for years. As of 2026, it has not activated. The technical implementation is well-understood; the holdup is the same as for other proposed soft forks - building broad enough community consensus to activate. It's discussed in roughly the same activation conversations as BIP-119 (CTV) and other covenant-adjacent proposals, with similar arguments for and against expanding Bitcoin's scripting flexibility.
See Eltoo for the flagship use case and Covenants for the broader expansion debate.
Key takeaways
- New SIGHASH type that loosens input binding
- Key for advanced Layer-2 designs (e.g., Eltoo)
- Still under active development and review