BIP-371 drops the finalizer clause from a Taproot PSBT field
Victoria Shinder1 min readA commit merged into the BIPs repository removes the finalizer clause from the description of PSBT_OUT_TAP_BIP32_DERIVATION in BIP-371, the proposal that defines Taproot fields for Partially Signed Bitcoin Transactions. The edit is to the per-output types table, where the field carries a 32-byte X-only public key involved in the output - the output key, the internal key, or a key present in a leaf script - together with a count of leaf hashes, the leaf hashes themselves, a 4-byte master key fingerprint and the derivation path as little-endian 32-bit indexes.
What it means
Output fields in a PSBT describe what is being created, not what has to be signed, and a finalizer's job is the input side. A clause telling implementers what a finalizer should do with an output-side derivation field was therefore instruction in the wrong place, and every implementer reading it had to decide whether to obey it.
Specification edits of this kind rarely change behaviour and often change compatibility, because two implementations that each resolved an ambiguous sentence differently now agree. That is worth more in a wallet interchange format than most feature additions.