INTRODUCING BIP-420: FORMAL BITCOIN IMPROVEMENT PROPOSAL FOR OP_CAT

Summary from the TLDR Crypto newsletter

The OP_CAT opcode has formally received proposal number 420. BIP-420 will allow two values to be concatenated in the Bitcoin scripting language. Though trivial in implementation, this feature greatly increases Bitcoin's functionality by introducing covenants that enable smart contracts, cryptographically secure bridges, zero-knowledge proof verification, and other useful features. OP_CAT has received much attention recently because the Taproot Wizards promoted the opcode through its Quantum Cats Ordinals.