Bitcoin XT was a fork of Bitcoin Core created by Mike Hearn in 2014. Originally designed to introduce alternative P2P rules, it later gained significant notoriety and support after its adoption of BIP 101 without community support in 2015, giving it importance in the block size limit controversy.

After Andresen’s resignation from the position of Bitcoin Core maintainer, he and Mike Hearn organized Bitcoin XT to address several controversial ideas lacking the consensus required to be implemented in Bitcoin Core.

BIP 101 was implemented in Bitcoin XT on August 6, 2015, and released on August 15.[4] If 75% of the last 1000 blocks were observed to have particular version bits set, it would have ceased enforcing the 1 MB block size limit and also have added a few new rules. However, this threshold was never achieved and no new XT blocks are being created today.

In January 2016, BIP 101 was removed from Bitcoin XT and replaced with the one-time block size increase to 2 MB present in Bitcoin Classic. In the year following this change, adoption of Bitcoin XT decreased dramatically, with fewer than 30 nodes remaining by January 2017.

Later attempts by other codebases to increase the block size to 2 MB including Bitcoin Classic and SegWit2x have also failed.

Miners

Miners that side with Bitcoin XT will produce blocks with a new version number.[8] This indicates to the rest of the network that they support XT.[8] When 75% of the last 1000 blocks are new-version blocks, these miners will automatically abandon Bitcoin and begin mining on a new Bitcoin XT blockchain.[8] This will begin after a waiting period of two weeks in hopes the economy in this time may force anyone who hasn’t switched yet to do so.[8]

Users and miners running full Bitcoin nodes will reject the XT blockchain starting with the first block that is larger than one megabyte in size, and thus be unaffected provided it fails to achieve economic consensus.

Users and merchants

If insufficient mining hash power runs XT to reach supermajority then nothing will happen. If enough does, XT users will follow a new blockchain and cease to be using and trading bitcoins.

Controversy

Later in January 2016, frustrated with his proposal being massively outvoted, Mike Hearn made a media stunt declaring on various US national and international press agencies that “Bitcoin has failed”. Max Keiser quoted Bram Cohen in describing Hearn’s move as “whiny rage quitting” and other members of the community pointed to an extensive account of manipulations http://gettopical.com/bitcoin/e289a9a5189008d994e80666e9038089 (unfortunately today many twitter screenshots are broken).

Bitcoin Unlimited

Bitcoin Unlimited “follows the release of Bitcoin XT and Bitcoin Classic”.

XT and Classic were two previous attempted hard forks that also failed. Like Classic and XT, Unlimited is also supported by a small group of Bitcoin mining pools.

With the Remote Exploit Crash bug discovered in Bitcoin Unlimited, the proposal went down the path of failure like XT and Classic.

The Remote Exploit Crash bug was the second major bug exposed in Unlimited and caused more than 350 Bitcoin Unlimited nodes to crash instantly.

The first bug occurred when a mining pool running Unlimited mined an invalid block, resulting in the loss of 13.2 BTC.

Like Classic, many of the Bitcoin Unlimited nodes were to be fake. New Unlimited nodes popped up in massive numbers at around the same time.

Bitcoin Classic

Bitcoin Classic was the second failed attempt to fork Bitcoin.

The proposal itself gained wide support from Bitcoin companies and a few mining pools.

Like XT, a lack of support for the proposal among the Bitcoin community as a whole led to the failure of this hard fork attempt.

Most of the Classic nodes that popped up were fake and hosted from the same ISP.

Bitcoin XT

Bitcoin XT was the first unsuccessful hard fork of Bitcoin.

Led by developers Gavin Andresen and Mike Hearn, XT attempted to raise the Bitcoin block size to 8 MB.

Despite support from a few large Bitcoin companies, the proposal failed to gain enough support from the community and Bitcoin users.

Frustrated with the lack of support for XT, Hearn labeled Bitcoin a failure, quit working on the project, and sold all of his bitcoins in January 2016.

Bitcoin’s price is up more than 300% since Hearn quit.

The Bitcoin Cash hard fork slated for Nov. 15 is getting closer and network participants are preparing for the upgrade in several ways.

On Oct. 22, the mining initiative SV-Pool, supported by Nchain and the firm’s chief scientist Craig Wright, announced the pool is now open to the public.

This means that Bitcoin Cash miners can direct their hash rate towards the SV-Pool and get paid by an initial pay-per-last-n-shares (PPLNS) system.

The pool details it plans to add more payment structures this November.

At the time of writing, according to Coin Dance statistics, SV-Pool has been capturing around 2.6 percent of the global BCH hashrate over the last seven days.

According to the pool’s recent announcement, SV-Pool says it stands by a “miners’ choice, miners first philosophy.” News.Bitcoin.com reported on the pool’s first mined block on Oct. 10 and at the time SV-Pool was using an invitation-only beta period.

During that time, the Bitcoin SV team launched its codebase and the Bitcoin Unlimited (BU) team also launched a new client.

The latest BU code is prepared for the Bitcoin ABC team’s ruleset changes and the team stated on Twitter that SV ruleset compatibility was “pending.” BU’s plan is to let the miners vote for features by using a system called the BIP135 bits standard.

Following the recent announcements concerning new clients and BIP135, the statistical data website Coin Dance has prepared its website for things like explicit mining pool support by proposal and a new politics and public opinion section.

The explicit mining pool support section, which seems to incorporate the most important data to most BCH proponents, currently says that “Voting should begin shortly.”

The politics and public opinion section is a different story as it shows a list of BCH-supporting businesses and organizations revealing specific proposal stances.

The Nov. 15 Bitcoin Cash network hard fork is approaching quickly and on Sunday the Bitcoin Unlimited (BU) programmers published BU version 1.5.0.

The latest BU client is fully compatible with the BCH chain and previous hard fork consensus changes that took place in the past.

BU’s 1.5.0 comes with some notable changes in contrast to the previous client release.

Team developer Andrea Suisani (Sickpig) detailed that the BU software includes canonical transaction ordering (CTOR), the opcode OP_Checkdatasigverify (CDSV), an enforced “clean stack” rule, a “push only” rule for script-sig, a 100-byte minimum transaction size and more.

This version means the BU implementation will be fully compatible with Bitcoin ABC’s ruleset changes, and on Twitter the developers have explained that SV support is “pending.”

On the Reddit forum r/btc, BU’s lead developer Andrew Stone explained he hopes miners use the voting system the team collaborated on with the Bitcoin XT developers.   

“What I would really like to see is miners start voting based on the BIP135 bits that we defined together with Bitcoin XT — Miners that support the Nov. 15 hard fork could start voting for the SV features they support,” Stone stated on the forum.

“Miners that don’t support the hard fork (even if that miner will follow the hash power majority come Nov. 15) should start using BIP135 to vote for the features it supports.

A vote for a feature is basically saying ‘I like the feature, but I want a different activation mechanism.’”

BIP135 Voting, Grace Periods, and Bitcoin SV

Stone further detailed that if there is a significant amount of votes showing a majority consensus then they should stop the November fork or start BIP135 activation.

The engineer continues by explaining that people don’t have to run BU to vote on these features as miners can set the BIP135 bits in their block version fields using mining pool software.

Following these statements, a BCH community member asked the programmer if the BIP135 system enabled the features automatically.