Some people have suggested repurposing OP_NOP3 as a new opcode, OP_CHECKSEQUENCEVERIFY.

What would the new opcode do? Why is it useful? Can't the signer choose the sequence field when they sign?

1 Answer 1


OP_CHECKSEQUENCEVERIFY (a.k.a OP_RELATIVECHECKLOCKTIMEVERIFY) can do relative lock times (used for sidechains and lightning).

It basically checks, if an input's sequence number is smaller than the sequence threshold (1 << 31 = 2147483648), and if so, it will compare the nLockTime against the sequence number of the input.

More info:

  • 4
    OP_CSV (BIP112) only constrains the nSequence value. The comparison of nSequence against time happens independently of OP_CSV's usage (BIP68). Commented Feb 8, 2016 at 2:41

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