It is official. Bitcoin Improvement Proposal 91 (BIP 91) locked in after 90 percent of all hash power supported the soft fork. Activation of Segregated Witness (SegWit) can become the next step, which makes BIP 148 unnecessary and August 1 a non-event.
Offered by Bitmain Warranty engineer James Hilliard, BIP 91 found support of multiple Bitcoin companies and mining pools. It is compatible with the New York Agreement as well as with BIP 148, another strategy to trigger the BIP 141 threshold indirectly.
However, technically SegWit activation is up in the air. There is a compulsory condition for SegWit activation – at least 95 percent of miners (by hash power) must signal their support for BIP 141 within next two weeks. If miners choose to support, they need to embed a piece of data called “bit 1” in the blocks they mine. This figure hasn’t been reached so far.
BIP 91 is one of the alternative strategies to trigger this threshold “indirectly”. Miners have been embedding “bit 4” in the blocks for the past couple of days. As a result, 269 blocks within a 336-block window included “bit 4” and BIP 91 soft fork locks in.
Now, miners should embed “bit 1” for the next two days. All BIP 91–compatible nodes will reject any block that doesn’t include “bit 1”.
If the majority of miners support BIP 91, they will control the longest valid chain consisting of bit 1 SegWit-signaling blocks only. In its turn, this will result in BIP 141 lock in approximately in the middle of August followed by SegWit activation.
The fact that majority of hash powers signaled “bit 4” for BIP 91 lock in doesn’t mean that they will signal “bit 1” for SegWit. Quite the opposite, now less than 50 percent of miners have signaled “bit 1”.
BIP 91 lock in is possible only due to hash power so miners can back out of BIP 91 with little more than reputational damage. If the majority of miners choose not to signal “bit 1”, they will still control the longest valid chain: valid according to most miners, and valid to most users.
Moreover, miners who do enforce the BIP 91 soft fork would then be forked off the Bitcoin network. They would mine blocks that will be ignored by the rest of the entire Bitcoin network.
Miners have already demonstrated their intention to start activating the SegWit soft fork within a couple of days by signaling “bit 4”. SegWit will be activated next week if miners stick to their stated choice.