Constant BIP65_ACTIVATION_MAINNET 

pub const BIP65_ACTIVATION_MAINNET: u64 = 388_381; // 388_381u64

BIP65: OP_CHECKLOCKTIMEVERIFY (CLTV) - Mainnet activation height

Starting at this block, CLTV opcode is enabled. Reference: BIP65, consensus activation at block 388,381