The lock in of the BIP91 proposal means that as long as 51% of the network hash power continues to mine blocks that support SegWit, the protocol will activate and there will be no risk of a major chain split.
BIP91 is a method of activating SegWit on the network as a result of what is known as the ‘New York Agreement’, which is very similar to the original BIP141 deployment method but with a few key differences:
The activation period is now 336 blocks, instead of the original 2016.
The activation threshold has been reduced to 80%, as opposed to the original 95%, which was deemed too high and impossible to achieve.
After this successful BIP91 lock in, miners signaling for BIP91 and running the BTC1 software developed by Jeff Garzik will start to reject all of the blocks which are not signaling for SegWit, which is very similar to the UASF (BIP148) concept. This should result in a successful SegWit activation since miners that aren’t signaling will effectively have their blocks constantly orphaned, leading to a significant loss in their mining revenue.
What is BIP91 ?
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 is a proposal by Bitmain Warranty (not to be confused with Bitmain) engineer James Hilliard which was specifically designed to prevent a coin-split by making SegWit2x and BIP148 compatible.
The proposal resembles BIP148 to some extent. Upon activation of BIP91, all BIP91 nodes will reject any blocks that do not signal support for SegWit through bit 1. As such, if a majority of miners (by hash power) run BIP91, the longest valid Bitcoin chain will consist of SegWit-signaling blocks only, and all regular BIP141 SegWit nodes will activate the protocol upgrade.
Where BIP91 differs from BIP148 is that it doesn’t have a set activation date, but is instead triggered by hash power. BIP91 nodes will reject any non-SegWit signalling blocks if, and only if, 80 percent of blocks first indicate within two days that’s what they’ll do.
With the news Bitcoin moving like rocket to $2900+ . Though there is some initial profit booking which pull it down .
Its a long relief.. Bitcoin has to go up..
All the Best !!