A Complete History of Bitcoin’s Consensus Forks

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Terminology

TermDefinition
ChainsplitA split in the blockchain, resulting in two separate chains with a common ancestor. Can occur due to hardforks, softforks, or neither.
HardforkA loosening of consensus rules, making previously invalid blocks valid. Requires node upgrades.
SoftforkA tightening of consensus rules, making previously valid blocks invalid. Existing nodes may not require upgrades.

(Originated April 2012, formalized in BIP99 and BIP123.)


List of Bitcoin Consensus Forks

DateActivation BlockBIP/VersionDescriptionTypeOutcome
28 Jul 2010n/a0.3.5Disabled OP_RETURN, fixing a critical bug allowing arbitrary Bitcoin spends.SoftforkSmooth upgrade, no issues.
31 Jul 2010n/a0.3.6Disabled OP_VER/OP_VERIF, removing DoS vectors.SoftforkUsers advised to upgrade or shut down.
15 Aug 201074,6380.3.10Fixed output-value-overflow bug post-184.5B BTC exploit.SoftforkChainsplit (51 "bad" blocks reversed).
12 Sept 201079,400n/aEnforced 1MB blocksize limit.SoftforkNo issues.
24 Mar 2013227,835BIP34Required block height in coinbase TX.Softfork95% threshold success.
11 Mar 2013225,4300.8.0Unplanned hardfork from BDB to LevelDB migration.N/AChainsplit (24 blocks), reverted.
14 Nov 2021709,632BIP341 (Taproot)Combined Schnorr signatures and MAST for privacy/scalability.Softfork90% miner activation success.

Key Takeaways

  1. Hardforks require network-wide upgrades (e.g., Taproot).
  2. Softforks maintain backward compatibility (e.g., SegWit).
  3. Chainsplits are rare but possible (e.g., 2010 overflow bug).

👉 Explore Bitcoin’s evolution for deeper insights.


FAQ

Q: What’s the difference between hardforks and softforks?
A: Hardforks relax rules, requiring upgrades; softforks tighten rules, often backward-compatible.

Q: Did Taproot cause a chainsplit?
A: No, it activated smoothly with 90% miner support.

Q: Why was the 1MB limit introduced?
A: To prevent spam attacks and ensure network stability (2010).

(Sources: BitMEX Research, Bitcoin Core GitHub, BIP documentation.)


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