The Bitcoin block size war was a dispute over how to increase Bitcoin's transaction capacity and who could authorise changes to its rules. Proposals in 2015–2017 ranged from larger blocks through a hard fork to Segregated Witness and payment-channel scaling. The disagreements concerned both technical limits and the authority of miners, businesses, developers, and users.123

Competing prioritiesReport an errorSuggest an improvement

Gavin Andresen's June 2015 BIP 101 proposed replacing the one-megabyte limit with an initial eight-megabyte limit and scheduled growth. Its motivation was to prevent limited transaction capacity from constraining Bitcoin adoption. The specification proposed a hard fork, requiring participating software to accept blocks that older rules would reject.1

Gregory Maxwell's December 2015 roadmap emphasised the cost of independent validation. He argued that excessive resource requirements could force users to trust intermediaries, while insufficient capacity could also make direct access too expensive. His proposed approach combined efficiency improvements, SegWit, and mechanisms such as payment channels.2

SegWit and activationReport an errorSuggest an improvement

BIP 141 separates witness data, including signatures, from the traditional transaction structure while committing to it within the block. Its block-weight rule discounts witness bytes and caps weight at four million units. This increases effective capacity without being a simple fourfold increase in the number of transactions. It also addresses transaction malleability for supported transactions, helping protocols that depend on stable transaction identifiers.4

Activation itself became contentious. BIP 148 specified that enforcing nodes would reject blocks without the required SegWit signal from 1 August 2017 until lock-in, subject to its activation conditions. BIP 91 offered miner coordination using an 80% threshold to require that signal. SegWit ultimately activated on 24 August 2017 at block 481,824.567

The forks and agreementsReport an errorSuggest an improvement

The May 2017 New York Agreement, published by Digital Currency Group, combined support for SegWit with a two-megabyte hard fork within six months. Bitcoin.org opposed the resulting SegWit2x proposal and argued that miner support could not alone redefine Bitcoin. Its objections included coin naming, replay risks, and treatment of customer balances.83

Bitcoin Cash split from Bitcoin on 1 August 2017. Its project website presents that split as a decision to pursue onchain scaling for low-cost everyday payments. It became a separate network rather than an agreed change applied to all Bitcoin users.9

The SegWit2x hard-fork effort was suspended in November 2017. In a contemporaneous statement, BitPay's Stephen Pair said its participation had aimed to reconcile the community, but that proceeding amid division would be harmful; he subsequently recorded supporters suspending the effort. The outcome left SegWit active on Bitcoin and Bitcoin Cash following a separate scaling path.1079

See alsoReport an errorSuggest an improvement

ReferencesReport an errorSuggest an improvement

  1. ^ a b Andresen, G. (2015). BIP 101: Increase maximum block size. https://bips.dev/101/ 

  2. ^ a b Maxwell, G. (2015-12-07). Capacity increases Roadmap for the Bitcoin system. https://bitcoincore.org/en/2015/12/07/roadmap/ 

  3. ^ a b Bitcoin.org (2017). Bitcoin.org to denounce “Segwit2x”. https://bitcoin.org/en/posts/denounce-segwit2x 

  4. ^ Lombrozo, E., Lau, J., and Wuille, P. BIP 141: Segregated Witness (Consensus layer). https://bips.dev/141/ 

  5. ^ Shaolin Fry (2017). BIP 148: Mandatory activation of segwit deployment. https://bips.dev/148/ 

  6. ^ Hilliard, J. (2017). BIP 91: Reduced threshold Segwit MASF. https://bips.dev/91/ 

  7. ^ a b Blockstream (2017-10-12). The Status of SegWit at Blockstream. https://blog.blockstream.com/en-the-status-of-segwit-at-blockstream/ 

  8. ^ Digital Currency Group (2017-05-23). Bitcoin Scaling Agreement at Consensus 2017. https://dcgco.medium.com/bitcoin-scaling-agreement-at-consensus-2017-133521fe9a77 

  9. ^ a b Bitcoin Cash. Peer-to-Peer Electronic Cash, project history. https://bitcoincash.org/ 

  10. ^ Pair, S. (2017-11-08). Segwit2x Should Be Canceled, including subsequent update. https://medium.com/@spair/segwit2x-should-be-canceled-b7399c767d34