Opcodes · reserved · reserved

OP_UNKNOWN212–255 (0xd4–0xff)

Bytes 0xd4 through 0xff (212–255) are undefined. A script fails if it executes one, which keeps them free for future upgrades. Libauth names them OP_UNKNOWN212 to OP_UNKNOWN255. BCHN names 0xd4 and 0xd5 OP_RESERVED3 and OP_RESERVED4, and 0xff INVALIDOPCODE. Byte 0xef also serves as the CashTokens token prefix: it marks token data placed ahead of an output's locking bytecode, outside the script the VM runs. As an opcode it stays undefined.