“It Might Be Hard Explaining Future Devs Why We Did These Things With OP_CAT” Says BIP Author

As builders continue to test out the Satoshi-era opcode, prominent Bitcoin community members say the code, known as OP_CAT, has verbose scripting language that may add risk to the oldest blockchain.

Even one of the authors behind the Bitcoin Improvement Proposal to add OP_CAT says the code is only part of what the network needs.

“CAT” offers the opportunity to build really powerful features in Bitcoin “in the least invasive way,” but it’s still limited, Armin Sabouri, CTO of Bitcoin Layer 2 Botanix Labs, said in an interview.

“I’d be in favor of activated CAT plus something else,” he said.

His voice dampens some of the hype surrounding OP_CAT, even though builders continue to experiment with the still-defunct code.

Sabouri co-authored BIP 347, which seeks to activate OP_CAT into the Bitcoin network after Satoshi removed it back in 2011.

Expanding Support

The more critical perspective for the upgrade comes as the code slowly makes its way through the Bitcoin ecosystem. Ordinal’s wallet Xverse revealed on June 12 that it’s expanding support for Bitcoin’s Signet testnet, which will enable testing experimental features, including OP_CAT.

Meanwhile, one of Ethereum’s main scaling solutions, StarkWare, is also putting its chips in OP_CAT as it plans to help scale Bitcoin.

“OP_CAT is good for everyone,” Bob Bodily, CEO of Bioniq, a Bitcoin Ordinals marketplace, said in an interview. But, he added, it has a “super verbose way of writing script,” which might frighten byte-conscientious developers.

Attack Vectors

That said, concerns about attack vectors –which Satoshi voiced back in 2011– may be overstated, while it would allow for Bitcoin to scale up to 40 multiples its current capacity, according to Bodily.

In 2019, one of the authors behind the Bitcoin Improvement Proposal that aims to add “CAT” to Bitcoin, Ethan Heilman, put out a request for Bitcoiners to find a new attack vector which might surface if OP_CAT was activated.

“Nobody stepped up,” Bodily claimed.

Bodily reckons it’s the best option for Bitcoin at the moment, as it will offer the network more expressiveness and enable more use-cases.

Potential For MEV

Another concern surrounding OP_CAT is the potential for MEV.

Maximal extractable value (MEV) is the maximum profit that blockchain miners and validators can make by including, excluding, and changing the order of transactions in a block. It has been at the center of several discussions in large networks like Ethereum, the latest linked to a $25 million dollar heist orchestrated by two brothers who gamed the system.

Matt Corrallo, a Bitcoin core contributor said in an April 16 post that systems that have arbitrarily expressible smart contracts are likely to have the potential for advanced MEV extraction similar to what we see on Ethereum today.

But Bodily said “most of that MEV might head to Layer 2s,” which would spare users on the main chain from dealing with the threat.

Satoshi-era Code

OP_CAT, short for “Operation Concatenate,” is an opcode that was initially proposed by Bitcoin’s creator, Satoshi Nakamoto. The opcode allows for the combination of two pieces of data into a single piece of data during the execution of a Bitcoin transaction.

Essentially, OP_CAT enables specific features that can limit or expand how bitcoin can be transacted in the future. Use-cases include secure vaults that would allow reversible transactions, automated recurring payments, or time-locked transfers for inheritance schemes.

But Satoshi Nakamoto removed OP_CAT in 2011, citing concerns that it would expose the network to security issues, such as denial-of-service (DoS) attacks if used in conjunction with other similar scripts.

“Cultish Behavior”

Detractors to activating OP_CAT have argued that Bitcoin’s creator removed the script for a reason, which the developer community is now ignoring.

Shinobi, the pseudonymous technical editor for Bitcoin Magazine, wrote on X on March 14 that the “If we don’t know the limits of what this can do or the potential effects it could have, adding it into Bitcoin sounds like a horrible idea, imo.”

In addition to Corrallo, Shinobi, and other detractors, is the laser-eyed Bitcoin maximalist camp. That intransigent minority has also been tagged as “ossifiers,” or believers that the network has achieved what it’s meant for–neutral money–and we should leave it at that.

Sabouri pushes back against the argument.

“When Satoshi deactivated CAT it already had a fix in it,” he said, and underscored a dangerous undercurrent with the idea. “We adopt a weird cultish behavior if we avoid the script just because Satoshi canceled it,” Sabouri said, adding that, “we likely understand Bitcoin now better than they did back then.”

Chances For Activation

OP_CAT is currently being tested in Signet, Bitcoin’s testnet which allows for validation signatures. And depending on who you ask, the chances for activation are either extremely low or a certainty.

Bodily said that Udi Wertheimer, a Bitcoin influencer who is in favor of the network adding OP_CAT places the chances at 100% for it to happen this year. Udi has been at the forefront of the so-called Bitcoin Season 2, which aims to add all sorts of features to a network he claims has been left behind.

On the other hand, renowned Bitcoin developer Jeremy Rubin, and author of another BIP–which would implement Covenants– thinks that the chances are 3% every year for the foreseeable future.

Sabouri, who told The Defiant that he isn’t going to be one of the developers activating the opcode, stands somewhere in the middle.

A Contentious BIP Number

Even the number attributed to OP_CAT’s BIP has been controversial. Although the official number is 347, people in the Taproot Wizards community are calling it 420.

“We like to say BIP 420 is a community assigned BIP number,” said Head of Product for Taproot Wizards Tyler Whittle, who is also the creator of the interactive BIP Land map which helps to better understand the road from proposal to activation in the Bitcoin ecosystem.

Whittle said in an interview even the BIP numbering process is another sign of gatekeeping by a select group of individuals.

“For a long time the only person who could assign BIP numbers was Luke Dash Jr. (one of Bitcoin’s core contributors), and he wasn’t giving OP_CAT one for no apparent reason,” Whittle said.

Next steps for OP_CAT is continued testing in Bitcoin’s Signet, while developers try to find any existential threat vectors that might arise from activating the opcode into Bitcoin Core.

As the interactive BIP Land map shows, the script might end up in “Testnet Graveyard” or move on to a Bitcoin Core pull request on Github. There is no set time frame for either scenario to play out, but according to Whittle, “Over the next month I think you’ll see more news come out about what people are building on signets with OP_CAT enabled.”