Without OP_CAT, Bruce Liu says Bitcoin is as "useful as a jumbo jet without wings" capable of much more than it’s allowed to do, but stuck on the ground while Ethereum and Solana soar.

Liu, the founder of OPCAT_Labs, says a single opcode, OP_CAT, could transform Bitcoin from static digital gold into programmable money that rivals other Layer-1 chains.

OP_CAT is a long-disabled opcode in Bitcoin’s code that, if re-enabled, would allow developers to concatenate data in scripts and unlock a range of new possibilities, from vaults and covenants to decentralized exchanges and zero-knowledge proofs.

The Bitcoin blockchain, if OP_CAT was re-enabled , would be as programmable as Ethereum or Solana, said Liu.

"OP_CAT is not new code. It was never deleted, just commented out and disabled. We are not adding my opcode or somebody else’s. It’s Satoshi’s,” Liu told CoinDesk during an interview on the sidelines of BTC Asia in Hong Kong.

But the push for OP_CAT doesn’t come without friction.

Satoshi disabled it in 201 0 over concerns it could enable denial-of-service attacks. Opponents argue that any new opcode introduces “unknown unknowns,” threatening Bitcoin’s hard-won stability. Others take a philosophical stance: Bitcoin should remain digital gold, rather than chasing Ethereum’s programmability.

Liu pushes back by appealing to Satoshi Nakamoto’s design.

“If Bitcoin was only for payments, why did Satoshi include Script at all?” he asked. “OP_CAT isn’t my invention, it’s Satoshi’s code. It was never deleted, only disabled.”

Liu says OP_CAT would bring Script to life – the basic programming language built into the Bitcoin blockchain – allowing Bitcoin to do more than just payments and enabling features like vaults or even basic DeFi.

OP_CAT, he said, would unlock more of that potential, letting developers build things like vaults, covenants, or even simple DeFi apps on Bitcoin.

To reinforce the point, he points back to Nakamoto’s own explanation of why Script existed in the first place.

In a 2010 Bitcointalk post , Nakamoto wrote that Bitcoin’s design was effectively “set in stone” from its first release, so he wanted it to accommodate every type of transaction he could imagine.

Hard-coding each one would have created endless special cases, Satoshi explained, so instead the Bitcoin creator introduced Script as a general solution that let users define their own conditions while nodes only needed to check if those conditions were met.

Already, the company launched a fork of Bitcoin in a virtual machine with OP_CAT enabled to demonstrate its potential, complete with SDKs, APIs and a JavaScript-like programming language designed to make building on Bitcoin accessible to Web2 developers.