Bitcoin Cash ABC vs. BCHSV: The 2018 Hard Fork and Hash War Explained

In November 2018, Bitcoin Cash (BCH) split into two competing chains: Bitcoin Cash ABC, backed by Roger Ver and Jihan Wu, and Bitcoin Cash SV (Satoshi's Vision), driven by Craig Wright and CoinGeek's Calvin Ayre. The disagreement was not about price but about protocol direction — ABC wanted ordered transactions and smart-contract groundwork, while SV wanted larger blocks and a return to the 2009 design. Because neither side added strong replay protection, the dispute escalated into a hash war, with miners pointing raw computing power at each chain to claim the dominant ledger and the BCH ticker.

Why Bitcoin Cash Forked in the First Place

Bitcoin Cash itself was born from a fork of the original Bitcoin chain on August 1, 2017. The split came out of a years-long scaling debate: one camp wanted to keep Bitcoin's blocks small and push transactions onto second layers, while another wanted bigger blocks so the base chain could handle more payments directly. The big-block camp created BCH and increased the block size limit, arguing that cheap, on-chain transactions were closer to the original peer-to-peer cash vision.

The early reference client was "Bitcoin ABC," where ABC stands for "Adjustable Blocksize Cap." Rather than hard-coding one block size forever, it let operators configure their own limit. This implementation drew its heaviest support from large mining pools and from high-profile backers including bitcoin.com's Roger Ver and Bitmain co-founder Jihan Wu.

📷 a simple timeline graphic showing BTC → BCH (Aug 2017) → BCH ABC + BCH SV (Nov 2018)

If you want the conceptual foundation before going deeper, our explainer on the difference between protocol-level upgrades is a useful companion: see our guide on soft forks versus hard forks.

ABC vs. SV: Two Competing Visions

The fork date was set for November 15, 2018. The split crystallized two factions with genuinely different roadmaps.

ABC followed a policy of forking roughly every six months to ship upgrades. The November release planned to add CTOR, which forces transactions into a deterministic order inside each block — a change the team argued would make future scaling and parallel validation easier. ABC also wanted a new script primitive to enable on-chain oracles and a handful of smaller fixes such as minimum transaction sizing.

SV took the opposite stance. Its central change was a much larger default block size of 128 MB, and it deliberately rejected CTOR and stripped the size limit on scripts. The longer-term ambition was to keep pushing the chain back toward the original 2009 Bitcoin design — even hinting at removing the block size cap entirely. Some of the proposals were openly contentious, including suggestions about dormant coins.

How a Disagreement Became a Hash War

The most dangerous detail was technical: a lack of clean separation between the two chains. Normally, a contentious hard fork ships with replay protection so that a transaction valid on one chain is invalid on the other. ABC implemented replay protection; SV intentionally mirrored it to cancel it out, leaving both chains vulnerable to a replay attack.

A replay attack happens when a transaction looks identical on both chains, so it can be "replayed" on the second ledger and lead to accidental double-spends. The same class of problem hit users in 2016 when Ethereum and Ethereum Classic split. If you want the parallel case study, see our breakdown of Ethereum Classic versus Ethereum.

With no separation, both camps declared they would direct all available hash power at their preferred chain. Craig Wright publicly threatened a 51% attack to guarantee SV's survival, and SV-aligned mining pools were estimated to control as much as 70% of network hash power going into the fork — the spark for the hash war.

📷 a chart showing BCH ABC vs. BCH SV share of network hashrate in the days after Nov 15, 2018

ABC's Playbook Against a 51% Attack

ABC was not defenseless. A chain under hash-power siege has several rational responses, and the economics often favor the defender because an attacker burns money for every block they orphan. The options on the table were:

1. Wait it out. Every block an attacker mines on a fork they then abandon is pure cost, so patience can simply drain the aggressor's treasury.
2. Mobilize more hash power. ABC supporters could redirect additional miners — even idle Bitcoin miners — onto the ABC chain to out-mine the attack.
3. Change the algorithm (the "nuclear option"). Fork again and swap the proof-of-work algorithm, instantly rendering the attacker's specialized hardware useless on the new chain.

That third option is the strategic trump card in any miner standoff: the moment you change the hashing function, billions of dollars of ASICs aimed at you become scrap metal for that chain.

What Actually Happened After the Fork

Reality was less explosive than the threats. Both sides mined some empty blocks early on, and there was never a clean 51% attack on the network. ABC quickly pulled ahead in accumulated hash power, and nearly every exchange assigned the BCH ticker to the ABC chain, with SV listed separately as BSV.

The fork did, however, ripple outward. In the days after November 15, the broader Bitcoin price fell sharply, and a meaningful share of that pressure was attributed to the hash war. Hardware that had been pointed at BTC was temporarily redirected toward BCH mining to fight the fork battle, reducing BTC's hash power and feeding a wider market sell-off. For a refresher on how that competition for blocks works, see our guide on how mining pools work.

By November 23, 2018, the SV camp had not surrendered — at one point on-chain trackers showed SV controlling roughly 53% of relevant hash power, and BSV's price had spiked over 50% in 24 hours. A standoff that had been declared "finished" several times was, in practice, still smoldering.

Worked Example: The Cost of Spite-Mining a Fork

To see why a hash war is mostly a contest of who can afford to lose more, run a simplified calculation. Suppose a faction commits 1 EH/s (exahash per second) to mining empty or quickly-orphaned blocks purely to suppress the rival chain.

• Assume electricity and overhead of roughly $0.05 per kWh and hardware drawing about 30 J/TH (joules per terahash).
• 1 EH/s = 1,000,000 TH/s, so power draw ≈ 1,000,000 × 30 J = 30,000,000 J/s = 30 MW.
• Over 24 hours that is 30 MW × 24 h = 720 MWh ≈ 720,000 kWh.
• At $0.05/kWh, that is about $36,000 per day in pure energy — before depreciation, and with effectively zero block-reward income if the blocks are orphaned.

Multiply that across a multi-week standoff and the attacker is voluntarily lighting hundreds of thousands of dollars on fire. This is exactly why ABC's "just wait" strategy was credible: the longer the assault ran, the more it bled the attacker. The numbers above are illustrative, but the direction is the lesson — sustained hash warfare is a wealth-destruction machine for everyone involved.

Risks and Pitfalls for Investors

The ABC/SV episode is a compact case study in fork risk. Watch for these:

• No replay protection. When a contentious split lacks replay protection, sending coins on one chain can unintentionally move them on the other. If you ever face a split, wait for exchanges and wallets to confirm replay-safe handling.
• Ticker ambiguity. Which chain inherits the original ticker is a market and exchange decision, not a settled fact at fork time. Always confirm exactly which asset you hold and are trading.
• Custody during chaos. Exchanges frequently freeze deposits and withdrawals around forks. Coins held on an exchange may be locked precisely when you most want to act.
• Concentrated hash power. A chain where one entity can muster a majority of hash power is structurally fragile, raising the odds of reorgs and double-spend attempts.
• Narrative-driven price spikes. Post-fork pumps (like BSV's 50%+ jump) are often liquidity-thin and reverse quickly. Treat hash-war headlines as volatility signals, not value signals.

COINOTAG Perspective

The ABC vs. SV war is best read not as a one-off feud but as a stress test of consensus mechanism economics. The episode proved two durable truths. First, social consensus — which client exchanges, wallets, and users actually run — ultimately decides which chain "wins" far more than raw hashrate threats. Second, a credible algorithm-change response makes pure 51%-attack blackmail a losing strategy, because the aggressor's hardware moat can be neutralized overnight. For long-term holders, the practical takeaway is unglamorous but reliable: in any contentious fork, do nothing risky until replay safety and ticker assignment are confirmed by the venues you actually use. The chain with the deepest ecosystem and exchange support almost always becomes the canonical asset, regardless of who shouts loudest about hash power.

📷 a side-by-side comparison card summarizing BCH (ABC) vs. BSV outcomes — ticker, ecosystem, market cap