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Bitcoin Cash fork

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Bitcoin Cash (BCH) is the durable chain bifurcation produced by the scaling conflict: a user-activated hard fork at block 478,558 on August 1, 2017, that raised the block-size limit to 8MB, rejected SegWit, and split from Bitcoin with replay protection so both chains could coexist. The fork's early history is unusually eventful — an Emergency Difficulty Adjustment that oscillated hashrate between chains and accelerated BCH issuance, a public contest over the "Bitcoin" name, the November 2018 "hash war" that split off Bitcoin SV, and a 2020 governance dispute that split off eCash — and its long arc is unusually clear: from roughly 8% of Bitcoin's market value at the fork to roughly 1% by 2026, with its expanded on-chain capacity persistently underutilized. BCH matters as the cleanest natural experiment in Bitcoin's history: the big-block design philosophy, implemented by capable people with substantial industrial backing, tested against the market. This note treats the fork and the chain; the governance conflict lives in Block Size Wars - History and the comparative fork record in Bitcoin forks - History.

Why this note matters

Every consequential claim about Bitcoin’s governance — that users rather than miners or companies control the protocol, that its monetary properties cannot be forked away, that the market prices decentralization — cites the Bitcoin Cash episode as its principal evidence. The episode carries that weight because it was a fair test: the big-block coalition had majority-hashrate sympathy, major-exchange support, the largest mining-hardware company, and a coherent design philosophy, and it still failed to carry the economy with it. The governance mechanics of the preceding conflict are treated in Block Size Wars - History and the pattern across all forks in Bitcoin forks - History; this note gives the fork itself the single-event depth those treatments defer.

The road to August 1

The fork was the exit ramp from a governance war this note only summarizes. By mid-2017, the multi-year block-size conflict had produced an activation standoff: SegWit — the Core-developer-track capacity-and-malleability upgrade — was stalled by miner non-signaling, the UASF (BIP 148) movement had committed economic nodes to enforcing SegWit by August 1 regardless of miner support, and the SegWit2x corporate compromise was attempting to buy miner activation with a promised later hard fork (see Block Size Wars - History and SegWit upgrade).

Inside the big-block coalition, a faction concluded that no activation path within Bitcoin would ever deliver meaningful on-chain scaling. In June 2017, developer Amaury Séchet announced Bitcoin ABC — a client implementing a user-activated hard fork: rather than fighting for activation thresholds, the software would simply begin enforcing different consensus rules at a scheduled time, splitting the chain for whoever followed. The UAHF was explicitly framed as a contingency against BIP 148 chaos and, in substance, as the big-block program’s declaration of independence. Roger Ver’s promotional reach, Jihan Wu’s Bitmain (whose internal contingency plan had sketched the UAHF concept), and the ViaBTC pool (which announced the “Bitcoin Cash” name and the first futures market) formed the launch coalition.

Fork mechanics

At block 478,558 (August 1, 2017, early afternoon UTC), nodes running the ABC ruleset diverged from Bitcoin:

  • Block size raised to 8MB — the coalition’s founding purpose (later raised to 32MB in May 2018).
  • SegWit rejected — BCH removed the upgrade entirely, keeping the pre-SegWit transaction format as a matter of design identity.
  • Replay protection via SIGHASH_FORKID — BCH signatures commit to a fork-specific flag, so a transaction valid on one chain is invalid on the other. This deserves emphasis: unlike the planned SegWit2x fork (which notoriously refused replay protection), BCH engineered a clean split — holders of pre-fork bitcoin simply held both coins, spendable independently. Whatever one thinks of the project, the split mechanics were responsible.
  • A new proof-of-work difficulty regime — as a minority-hashrate chain, BCH could not inherit Bitcoin’s difficulty, so it added an Emergency Difficulty Adjustment (EDA) allowing rapid downward retargeting when blocks came slowly.
  • A distinct address format (CashAddr, January 2018) — added after months of costly user confusion from the shared legacy format.

Every pre-fork UTXO existed on both chains, so the fork functioned as an airdrop: every bitcoin holder received an equal BCH balance, and the market’s subsequent relative pricing of the two chains became a continuous referendum on the two design philosophies.

The EDA episode

The Emergency Difficulty Adjustment kept the minority chain alive — and then nearly discredited it. Because the EDA cut difficulty sharply after slow stretches while Bitcoin’s difficulty stood still, profit-switching miners oscillated en masse: mine BCH while its difficulty was crashed, abandon it once difficulty recovered, wait for the next crash. Through autumn 2017 the BCH chain lurched between hour-long block droughts and minutes-apart block floods; the accelerated stretches pushed BCH’s cumulative issuance tens of thousands of coins ahead of Bitcoin’s schedule, permanently steepening its early supply curve. Bitcoin’s own block production, anchored by its unmodified retargeting, was untouched throughout (see Difficulty adjustment).

The episode was fixed on November 13, 2017, with a new rolling difficulty-adjustment algorithm (DAA), and it left two durable lessons: consensus-parameter design under adversarial incentives is unforgiving — the EDA was a rational patch with an exploitable dynamic its designers did not intend — and a minority-hashrate chain lives at the sufferance of profit-switching miners, a structural fragility no later BCH upgrade removed.

The contest for the name

BCH launched claiming not merely legitimacy but identity: the fork, in its supporters’ telling, was Bitcoin — the restoration of Satoshi’s peer-to-peer-cash design from a developer clique that had captured it. The claim was pressed through Ver’s bitcoin.com (whose wallet and site framing led many newcomers to buy BCH believing it was Bitcoin), through the r/btc forum, and through a brief November 2017 market episode — after SegWit2x’s cancellation — when BCH’s price tripled in days amid open “flippening” talk and coordinated hashrate shifts.

The contest resolved through no formal mechanism, which is the point of the episode. Exchanges converged on the BCH ticker and the “Bitcoin Cash” label; wallets, merchants, media, and eventually courts and regulators followed the same social consensus; the brief price surge reversed. The name “Bitcoin” proved to be held by the network’s users collectively — not by miners, not by companies, not by the loudest claimants — which is the social-layer counterpart of the governance lesson in Block Size Wars - History. The identity claim’s later, stranger chapter — Craig Wright’s — belongs to the next section and to Craig Wright and the Faketoshi controversy.

The hash war and the BSV split

In November 2018, the BCH coalition split along the same fault line it had itself created: a scheduled protocol upgrade (BCH hard-forks on a fixed twice-yearly cadence — itself a notable governance contrast with Bitcoin’s consensus-gated upgrades, see How upgrades happen) became a contest between Bitcoin ABC’s roadmap and a faction led by Craig Wright and Calvin Ayre demanding bigger blocks (128MB) and restored original-protocol opcodes under the banner “Satoshi’s Vision.”

The November 15 fork became an open hashrate battle — both sides renting and redirecting enormous SHA-256 capacity (much of it borrowed from Bitcoin mining) to out-mine the other, amid threats to 51%-attack the rival chain. The ABC side, backed by Ver and Wu, retained the BCH ticker and ecosystem; the Wright–Ayre chain became Bitcoin SV (see Bitcoin SV fork (not yet built) and, for the chronicle-level treatment, Bitcoin forks - History). Two details outlived the week. ABC added protocol-level checkpointing to prevent deep reorganization by hostile hashrate — a security-model concession that a minority proof-of-work chain cannot, in fact, rely on proof-of-work alone. And the spectacle of leaders openly directing hashrate as a weapon made explicit how far the fork ecosystem’s governance had drifted from the credible neutrality both chains claimed to embody.

Later splits and the ecosystem after

The fragmentation continued. In November 2020, a dispute over Bitcoin ABC’s proposed “Infrastructure Funding Plan” — redirecting 8% of the block reward to a developer fund — ended with the ecosystem siding against its own founding client: the community-run BCHN node displaced ABC, and Séchet’s chain continued separately as eCash (XEC). The project that began by rejecting one developer team’s authority had, within three years, deposed its own lead developer over a self-funding proposal — evidence that the governance instability was structural rather than personal.

The chain itself has continued operating without interruption: twice-yearly upgrades, a small committed developer and user community, real (if modest) payments usage in a few niches. The empirical record on its founding thesis, though, is stark — BCH’s expanded capacity has run persistently far below its ceiling, its transaction volumes a small fraction of Bitcoin’s, while Bitcoin’s fee-market and layered-scaling path (see The Lightning Network) absorbed the demand the big-block thesis predicted would migrate. By 2026 BCH trades at roughly 1% of Bitcoin’s market value, down from ~8% at the fork and ~25% at its December 2017 peak.

Counter-arguments and tensions

This note’s framing — BCH as the failed empirical test of the big-block philosophy — has serious counter-readings: that BCH is a legitimate ongoing experiment whose value is not exhausted by its exchange rate; that the 2017 split was a healthy mechanism (a peaceful divorce beats a captured protocol, and both communities got the chain they wanted); and that Bitcoin’s small-block victory owed as much to incumbency, brand, and exchange-listing inertia as to design merit. The first and third are engaged substantively, with responses, in Bitcoin forks - History § Counter-arguments; the peaceful-divorce reading has genuine merit and is partially absorbed into this note’s acknowledgment that the split mechanics were responsible and the coexistence stable. For the broader critique that contentious forks reveal a governance weakness in Bitcoin itself, see the governance treatment in Block Size Wars - History and the engagement in Development and governance.

Open questions for further development

  • BCH retains a genuine low-fee on-chain payments niche in a few regions and merchant communities. Is there a durable equilibrium for a specialist payments chain at ~1% relative scale, or does security-budget decay (fee revenue on a low-fee chain, post-subsidy) make the position terminal?
  • The checkpointing concession has never been fully analyzed in this area’s notes: what is the honest security model of a minority SHA-256 chain that shares its hardware base with a vastly larger rival?
  • The fixed twice-yearly upgrade cadence is a real governance alternative to Bitcoin’s consensus-gated model — arguably BCH’s most interesting ongoing experiment. What has it actually produced, and at what cost in splits?

Canonical sources for this note

Primary documents

  • The Bitcoin ABC UAHF specification and announcement materials (June–July 2017) — the fork’s technical self-definition, including SIGHASH_FORKID replay protection.
  • The BCH DAA specification (November 2017) — the EDA fix; the primary record of the difficulty episode.
  • Contemporary exchange and wallet policy announcements (August–November 2017) — the primary record of the ticker/naming resolution.

Secondary and historical treatments

  • The Blocksize War (book) - Jonathan Bier — the canonical chronicle; its closing chapters cover the UAHF, the fork, and the November 2017 endgame in detail.
  • Pete Rizzo’s retrospective journalism on the fork and the hash war — careful post-resolution reconstruction.
  • Contemporaneous technical analyses of the EDA oscillation (mining-pool and developer write-ups, autumn 2017) — the quantitative record of the issuance acceleration.

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