Today, Bitcoin Script answers one question: who may spend this coin? A covenant would also restrict how it can be spent, for example "only to this exact set of outputs" or "only to a vault address after a delay".
Status
As of October 2026, no general covenant opcode is active on Bitcoin. Proposals such as CTV (BIP119), OP_CAT (BIP347), CHECKSIGFROMSTACK (BIP348) and OP_CHECKCONTRACTVERIFY (BIP443) would each need a soft fork.
Why people want them
Vaults that protect against key theft, cheaper shared UTXOs, and more efficient layer-2 designs such as Ark and channel factories.
Why people are careful
Some designs could let coins be restricted forever ("recursive" covenants), and any consensus change is hard to undo.