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Now the SegWit2x Hard Fork Has Really Failed to Activate


           Now the SegWit2x Hard Fork Has Really Failed to Activate

In case there were any remaining doubts, it now seems clear that the SegWit2x hard fork will not happen.

The SegWit2x project, a product of the New York Agreement signed onto by a long list of companies and miners in May, had scheduled a hard fork to double Bitcoin’s block weight limit today. And while the controversial effort was suspended by leaders of the project last week, this would not have stopped anyone else from proceeding with it. Companies like Coinbase were indeed taking into account that the SegWit2x hard fork could still happen.

The Fork That Wasn’t

SegWit2x nodes — most notably btc1 — were programmed to fork away from the Bitcoin blockchain this afternoon (UTC) to create the SegWit2x blockchain and a new currency, often referred to as B2X. However, not a single SegWit2x block has been mined since fork point, nor is there any indication that this is likely to happen. For all intents and purposes, there is no SegWit2x — nor a B2X.

Further, software bugs in the btc1 codebase made all btc1 implementations grind to a halt even before it reached the expected fork point. While Bitcoin and SegWit2x nodes were widely expected to share a single blockchain up until block 494783 and then to go their own ways at block 494784, btc1 nodes never made it past block 494782.

This is mainly because the first block on the SegWit2x chain was required to have a “base block” larger than one megabyte. This is how the chain would diverge from the original Bitcoin protocol. But due to what is referred to as an “off-by-one error,” SegWit2x blocks started to reject smaller-than-one-megabyte blocks one block too soon — at block 494,783 instead of 494,784.

Moreover, another btc1 bug prevented miners from mining a big enough block when it was needed. So even if some miners did want to proceed with the fork, they accidentally wouldn’t have done so — at least not automatically. Miners would instead have had to manually configure their block weight settings, but it’s unlikely they knew about this step. Btc1 maintainer Jeff Garzik (while also denying there was a problem) has since released a patch to resolve this issue.

But judging by the absence of any SegWit2x blocks, the patch hasn’t made a difference, most likely because few, if any, miners were interested in mining on the SegWit2x chain in the first place.


Despite the seeming failure of SegWit2x to take off in any way, it should be noted that there is technically no way to declare a fork like SegWit2x officially “dead” or “failed.”

While unlikely, it’s always possible that the SegWit2x hard fork could proceed at some point in the future. In fact, there is no way to tell whether the SegWit2x chain is currently being mined with a little bit of hash power right now, and it is strictly impossible to foresee whether it will be mined later on. Perhaps a SegWit2x block will be found a day from now, a week from now or even ten years from now, at which point SegWit2x and B2X will technically come into existence.

However, since the SegWit2x chain did not include a mining difficulty reset, it will be as hard to mine a B2X block as it currently is to mine a BTC block. Meanwhile, market support for B2X appears to be extremely low, with B2X futures trading below 2 percent of BTC. So even if miners decide to mine B2X blocks, they’d almost certainly be earning far less than they would by mining BTC. Or, more accurately, they’d spend more on electricity bills than they’d be able to earn by mining B2X. The financial incentive to mine the SegWit2x chain just isn’t there.

Alternatively, SegWit2x could see a bit of a rebirth in the form of “BitcoinX” (BTX). This project, supposedly started by disappointed SegWit2x supporters, will take a snapshot of bitcoin balances at block height 494,783 and start a SegWit2x-like altcoin that offers all BTC holders the equivalent amount in BTX. Though, while this coin is arguably more viable than B2X thanks to a mining difficulty reset and more, it really is a new coin — arguably even more so than B2X would have been.

Aaron van Wirdum retouched by


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