# OP_RETURN

URL: https://blockspace.wiki/glossary/op-return/

An output whose script begins with `OP_RETURN` (0x6a), which makes it provably unspendable; Bitcoin Core never adds it to the UTXO set. Its bytes are non-witness, so each costs one vbyte. Consensus has never limited its size; the limits are relay policy, and Bitcoin Core 30.0 raised the default to 100,000 bytes and allowed several such outputs per transaction. The data-types reference lists Runes, alkanes protostones, small Counterparty messages, Omni Class C, Pipe and Charms among its users. BTI attributes the whole output serialization: 8 value bytes, the script length and the script.

Sources:

- block.space docs: data types · https://block.space/docs/datatypes

Updated: 2026-10-20