What Is BIP91 and Why Does It Matter?

With the Bitcoin scaling deadline drawing closer, people are getting anxious regarding what the future may hold. SegWit2x and the user-activated soft fork are not mutually exclusive; it appears they may still cause a chain split. The BIP 91 proposal is designed to counter this problem and make both SegWit2x and BIP148 compatible. In the best-case scenario, this patch will prevent a Bitcoin split come August 1st.

BIP91 May Save Bitcoin After All

The vast majority of Bitcoin enthusiasts do not want to see a chain split, as such an event would be disastrous for the entire ecosystem. Having multiple Bitcoin blockchains competing with one another would cause disruption and create a turbulent price. It is certainly possible that there could be different iterations of Bitcoin itself at some point, even if the longevity of each were short.

BIP91 is one way to prevent this from happening. This particular project is created by James Hilliard, an engineer of Bitmain Warranty, which is a company very different from Bitmain, the mining hardware manufacturer. The goal of BIP91 is to prevent a chain split from happening by makeing BIP148 and SegWit2x compatible with one another. Considering how both concepts will activate on the network within 36 hours of one another, compatibility is of the utmost importance.

How does BIP91 work exactly? At first glance, one immediately sees some resemblance with BIP148. Once BIP91 activates on the Bitcoin network, all of the network nodes signaling this solution will reject blocks which are not SegWit compatible. This is exactly what BIP148 aims to achieve as well, as its top priority is to ensure that Segregated Witness activates on the Bitcoin network once and for all. Assuming that the BIP91 chain will be the largest blockchain in existence, it will only support SegWit-signaling blocks.

And that is where most of the similarities between BIP91 and BIP148 end. The biggest difference is that BIP91 has no official flag day or activation date in place, though it requires significant means of hashpower to support it. We have seen such an approach before with the initial SegWit activation period, which was easily countered by competing implementations of the Bitcoin client. Bitcoin Unlimited, for example, easily blocked Segregated Witness from activating originally.

All BIP91 network nodes would reject non-SegWit signaling blocks if 80 percent of network blocks first indicate that is what will happen. Choosing this golden path between BIP148 and SegWit2x would allow both parties to get what they want: we would see the activation of SegWit2x with its 80% mining support threshold, while still also honoring the original SegWit proposal. This BIP would have to gain sufficient traction before August 1st, the date on which the UASF goes into effect.

Judging by the information from Coin Dance — which may need to be updated — BIP91 has 9.5% hashpower support already. However, over 60% of the Bitcoin blocks mined over the past 24 hours support BIP91, which is a strong indication that this new solution may effectively get enough traction to prevent a chain split. The coming two weeks will be incredibly important for Bitcoin, to say the least. BIP91 may be one of the more important scaling solutions Bitcoin has seen to date.