Advocates of restoring a Satoshi-era command in Bitcoin's programming language have introduced new code that includes the number 420 as the change's purported BIP number. The code, known as OP_CAT, aims to expand the toolbox of Bitcoin developers by enabling the creation of covenants on Bitcoin, which can be used in areas like automated payments and reversible transactions. The proposal's renewed framing comes as developers push the technical envelope on Bitcoin in other ways.