CLTV (BIP-65)
CLTV - CheckLockTimeVerify (BIP-65)
| Year | 2015 |
| Type | Soft fork (MASF) |
| BIP | BIP-65 |
| Status | Active |
What it does
Adds the OP_CHECKLOCKTIMEVERIFY opcode, which allows a transaction output to be made unspendable until a specific block height or time. This enables absolute time locks at the script level.
Why it mattered
- Enabled trustless payment channels (predecessor to Lightning)
- Made escrow and time-locked contracts possible without third parties
- Critical building block for layer-2 protocols
How it activated
Miner-activated soft fork using BIP-34-style version bits. Required 750 of the last 1000 blocks. Activated in December 2015.
Outcome
Smooth activation, no chain split. CLTV is now fundamental to Lightning Network and other time-locked constructs.