Cointelegraph Research describes MATT as a proposed Bitcoin smart contract framework that would carry contract state across transactions. Its proposed OP_CCV implementation would let scripts check that a Taproot output commits to updated state; the article does not describe it as an active Bitcoin feature.
Combined with OP_CAT, the framework could verify Merkle proofs on-chain and support fraud proofs that reveal only a disputed computation step. That use would require the computation to be represented as steps committed in a Merkle tree. In OP_CCV’s default and deduct modes, fees would need separate fee-paying inputs.
