OP_TXHASH

OP_TXHASH is a proposed, experimental Bitcoin opcode described in BIP 346, authored by Steven Roose and Brandon Black. It is not active in Bitcoin consensus and would require a soft fork. We present it neutrally as one of several covenant-enabling ideas under discussion as of 2026, with no activation scheduled.

How it works

OP_TXHASH would activate as new semantics for an OP_SUCCESS opcode inside Tapscript. It produces a hash over a caller-chosen set of transaction fields, selected via a structure called a TxFieldSelector. A script can then require that hash to equal a committed value, enforcing that specific inputs, outputs, or global fields are spent exactly as pre-defined while leaving other fields free to change at spending time.

Comparison to CTV

OP_CHECKTEMPLATEVERIFY (CTV) commits to an entire transaction template. OP_TXHASH is sometimes described as a more granular relative: it lets the author pick precisely which pieces of a transaction are constrained and which remain flexible. Proponents argue this granularity improves privacy and coordination in multiparty and Layer 2 protocols, since participants only fix the parts that matter to the contract. Critics raise the usual covenant questions about added Script complexity and long-term consensus surface, and the proposal remains a topic of active, respectful debate.

OP_TXHASH is closely related to OP_CHECKCONTRACTVERIFY and to signature-introspection primitives like OP_CHECKSIGFROMSTACK. See also our overview of MATT.