OP_PAIRCOMMIT
BIP 442, PAIRCOMMIT
A proposed tapscript opcode that hashes two stack elements into one tagged commitment, enabling Merkle-style commitments inside script.
OP_PAIRCOMMIT is a draft opcode proposed in BIP 442 for Taproot script spends. When executed, it takes the top two stack elements, hashes them together with a tagged hash construction, and pushes one 32-byte commitment back onto the stack.
Bitcoin script already has simple ways to commit to single items with hashes. OP_PAIRCOMMIT adds a compact way to commit to pairs of items, and repeated applications can build Merkle-style commitments to larger sets of data. That makes it useful for advanced contracts that need to commit to structured data while revealing only the branch being used.
The proposal is discussed as a building block for more expressive tapscript contracts, including designs that need better in-script data commitments or staged delegation logic. It is also one of the opcode candidates discussed in the broader LNHANCE proposal set.