At a recent SF Bitcoin Developers meetup, Bitcoin Core contributor and Blockstream CTO Greg Maxwell provided a technical presentation on the upcoming 0.15 release of Bitcoin Core. During the Q&A portion of his talk, Blocktime co-host Michael Tidwell asked Maxwell for his thoughts on SegWit2x and specifically what he thinks would happen in a situation where the hard fork portion of the proposal gains majority support from the network hashrate.

SegWit2x came out of the New York Agreement where large Bitcoin companies and the vast majority of the network hashrate agreed to implement a hard-forking increase to the block weight limit in November; however, some signers have already backed out of the deal or clarified that they were never for the hard fork portion of the agreement.

In his response to Tidwell’s question, Maxwell noted that the major contributors to Bitcoin Core are not interested in SegWit2x and will not implement it.

“I think it’s unlikely that [SegWit2x] will get more work behind it for the same reason that miners are mining [Bitcoin Cash] right now,” said Maxwell of the prospects of the proposal. “Miners are going to follow the money.”

The ‘Most Work’ Chain is Not What Matters

From Maxwell’s perspective, Bitcoin is defined by the rules of the system rather than the desires of the majority of the network hashrate.

“More work is always secondary to following the rules of Bitcoin, said Mawell.”

To further his point, Maxwell noted that there may have already been situations where Ethereum has had more joules of energy pumped into its mining process than Bitcoin.

“I don’t just suddenly go, ‘Oh, Ethereum is Bitcoin now because it’s got more joules of energy pumped into its security,’”

It is Possible for Bitcoin to Hard Fork, But It’s Hard

Although Maxwell is against the SegWit2x proposal, he did concede that it is possible for Bitcoin to hard fork in the future.

“But it has to be a hard fork the users as a whole choose to do,” Maxwell clarified. “Maybe that’s really hard to achieve, especially since we can do so many things without hard forks.”

The contributors to Bitcoin Core tend to prefer soft forks over hard forks because they’re backwards compatible and can be rolled out on an opt-in basis.

“That’s an important part of the security model because if you can easily change Bitcoin to take one controversial, probably okay change, then you can change it in lots of other ways as well,” Maxwell added.

According to Maxwell, bitcoin’s value proposition is as a “digital asset that isn’t going to change out from under you”.

In terms of the types of hard forks that could work, Maxwell noted that one potential process is to add a soft-forking change to Bitcoin and then use a hard fork to clean up the technical debt related to the change at a later date. Maxwell believes it would be much easier to gain social consensus around these sorts of hard forks.

“There is a proportional relationship [between] the distance you have to the code — and the operation of the system — and how viable you think some of these proposals are,” Maxwell later added about hard fork proposals more generally.

How Would Bitcoin Core Contributors React to SegWit2x?

In terms of how the contributors to Bitcoin Core may react to SegWit2x gaining the majority of the network hashrate, Maxwell first reiterated that the proposal would probably only gain majority support from miners if users as a whole were adopting it.

“I think that if users as a whole were adopting it, then the people that are developing Bitcoin today would go and do something else instead, said Maxwell”

In a situation where the majority of miners are supporting SegWit2x and users still prefer the original chain, Maxwell noted that a change to Bitcoin’s proof-of-work algorithm (SHA-256) would “make sense”. The Blockstream CTO does not view SHA-256 as a defining trait of the Bitcoin system, and he noted that it may need to be changed in the future for security reasons anyway.

Changing the proof-of-work algorithm would effectively destroy the investments bitcoin miners have made into specialized hardware used for the mining process. Maxwell referred to this as a “nuclear option”.

“When you have no other choice, you do it because duh,” Maxwell added. “Do you choose a system that’s non-functional and insecure or do you choose a system that works?”