Distributed database that is used to maintain a continuously growing list of records, called blocks
Segregated Witness, defined by BIP141, locks in if at least 95% of miners signal support for the upgrade within a two-week difficulty period. In order to do so, miners need to embed a piece of data called “bit 1” in the blocks they mine. This is technically the only way for SegWit to be activated right now.
However, there are some alternative strategies to reach this threshold “indirectly” — those like BIP91.
BIP91 is a Bitcoin Improvement Proposal adopted due to the New York Agreement and supported by a number of Bitcoin companies and mining pools.
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Bitcoin Improvement Proposal 91 (BIP91) has just locked in as up to 90% of all hash power signaled support for this softfork signaled in support of this decision. The next step is to be the activation of Segregated Witness (SegWit). As a result, this should make BIP148 obsolete and the risk of chain split on August 1st will be avoided.
Proposal Activation Spotlight by coin.dance
Thus, miners have been signaling support for BIP91 over the past couple of days through another piece of data, “bit 4.” Once 269 blocks within a 336-block window include bit 4, this BIP91 soft fork gets locked in. And this is exactly what just happened.
Congratulations Bitcoin! BIP91 will lock in this period and we will finally get SegWit on Bitcoin! https://t.co/0cJEQbXWJJ
— Charlie Lee (@SatoshiLite) 21 июля 2017 г.
After another 336 blocks, a little over two days from now, all BIP91-compatible nodes will reject any block that doesn’t include bit 1.
As long as a majority of hash power enforces BIP91, this majority should eventually control the longest valid chain according to all Bitcoin nodes. And as this chain consists of bit 1 SegWit-signaling blocks only, it would in turn activate SegWit on all SegWit-ready nodes.
In this case, BIP141 should lock in by mid-August, and SegWit should be live on the Bitcoin network after a two-week “grace period” by the end of the month.