Transaction: 51bae58fa9d413b86d74da60d5366987dcdeb0586d39b93b2ca22f9e40dc83de.

Block: 856182

OP_CAT is one of many proposals trying to find their way into Bitcoin Core, though it is not strictly a covenant proposal, but a way to concatenate elements from the Stack onto a Script. OP_CAT could mimic the behavior of many others.

Covenants, which are nothing more than specific spending conditions, enable many improvements to the Lightning Network, coordinatorless coinjoins, BitVM, L2 bridges, and many other things that cannot be done properly in Bitcoin today due to the lack of expressiveness of Script.

OP_CAT transactions, while non-standard, are valid because nodes that do not enforce OP_CAT only need to read it as OP_SUCCESS. The only way to get OP_CAT out of Bitcoin is to reorganize or hard fork the chain.