SegWit2x was a proposed hard fork of the cryptocurrency Bitcoin. The fork was slated to occur on 16 November 2017, but was cancelled due to lack of consensus. The fork would have increased the block size to 2 megabytes. Segregated Witness has been previously activated on the Bitcoin chain from which SegWit2x would have forked.
The implementation of Segregated Witness in August 2017 was the first half of the so-called "New York Agreement" in which those who wanted to increase effective block size by SegWit compromised with those who wanted to increase block size by a hard fork to a larger block size. The second half of SegWit2X involves a hard fork in November 2017 to increase the blocksize to 2 megabytes. Some companies that originally supported the New York Agreement backed-out, including F2Pool, Bitwala and Wayniloans.
A major issue of contention was the choice by the SegWit2x developer not to implement mandatory replay protection. Opt-in replay protection means that the Segwit2x chain will still accept transactions intended for the original chain, in addition to replay-protected transactions only valid on Segwit2x. Users sending transactions on the Bitcoin chain, or who failed to send replay-protected Segwit2x transactions, would have been vulnerable to having their transactions replayed to the other chain, resulting in accidental loss of funds. This absence of strong replay protection has created considerable controversy in the bitcoin community.
Although the stated reason for the cancellation of the hardfork was "lack of consensus", several bugs in the codebase would have prevented the fork from occurring. The official fork was planned to occur at block height 494,784, however the actual code stalled waiting for block height 494,783 due to an off-by-one coding error.
- Haywood, Matthew (16 August 2017). "Segwit2x, 'The New York Agreement'". bravenewcoin.com. Retrieved 6 October 2017.
- Hertig, Alyssa (12 July 2017). "Explainer: What Is SegWit2x and What Does It Mean for Bitcoin?". CoinDesk. Retrieved 6 October 2017.
- tendencialglobal (18 September 2017). "Segwit2X loses support between mining groups and blockchain companies". cryptocurrency. Steemit. Retrieved 7 October 2017.
- "List of Segwit2x contributors". Retrieved 10 December 2017.
- "segwit2x-announce should mention how to safely opt-out of changes #10". Retrieved 10 December 2017.
- Song, Jimmy (4 October 2017). "How Segwit2x Replay Protection Works". bitcointechtalk.com. Retrieved 6 October 2017.
- van Wirdum, Aaron (22 September 2017). "SegWit2X and the Case for Strong Replay Protection (And Why It's Controversial)". Bitcoin Magazine. Retrieved 6 October 2017.
- Hertig, Alyssa (8 November 2017). "2x Called Off: Bitcoin Hard Fork Suspended for Lack of Consensus". CoinDesk. Retrieved 8 November 2017.
- Vigna, Paul (8 November 2017). "Bitcoin Dodges Split That Threatened Its Surging Price". The Wall Street Journal. Retrieved 8 November 2017.
- "Segwit2x Final Steps". 8 November 2017. Retrieved 1 December 2017.
- Song, Jimmy (20 November 2017). "Segwit2x Bugs Explained". Retrieved 1 December 2017.
- Akolkar, Bhushan (18 November 2017). "Amidst Doubts, the SegWit2x Hard Fork Fails to Get Activated". Retrieved 10 December 2017.
- "Bitcoin Proposal Support by Block (historical) Summary". Retrieved 10 December 2017.
- "Network Snapshot of Satoshi:1.14.5 Nodes". Retrieved 10 December 2017.