dailybtclore on Nostr: July 4, 2015 — BIP66 Activation Causes 6-Block Chainsplit Of all the Bitcoin ...
July 4, 2015 — BIP66 Activation Causes 6-Block Chainsplit
Of all the Bitcoin upgrades that could have caused a crisis, BIP66 was the least likely candidate. Pieter Wuille's proposal was a cleanup: require strict DER encoding on signatures. No controversy, no competing visions. Just a boring standards fix. 95% of miners had signaled support.
Then it activated on July 4, 2015 — and split the chain.
An unknown miner produced a block violating the new DER rules. Six large pools built on top of it without checking it. They were running SPV mining: processing block headers only, skipping full block validation. The invalid chain grew 6 blocks deep before a forced reorg corrected it.
The revelation wasn't technical. It was about trust. Those six pools had signaled support for a rule they weren't enforcing. The upgrade infrastructure had been running on the honor system. It hadn't held.
The incident fed directly into 2017's SegWit debates. The case for user-activated soft forks was partly an answer to what BIP66 had exposed: miner signaling and miner readiness are not the same thing.
#bitcoin #bitcoinhistory
Published at
2026-07-04 14:45:39 UTCEvent JSON
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"content": "July 4, 2015 — BIP66 Activation Causes 6-Block Chainsplit\n\nOf all the Bitcoin upgrades that could have caused a crisis, BIP66 was the least likely candidate. Pieter Wuille's proposal was a cleanup: require strict DER encoding on signatures. No controversy, no competing visions. Just a boring standards fix. 95% of miners had signaled support.\n\nThen it activated on July 4, 2015 — and split the chain.\n\nAn unknown miner produced a block violating the new DER rules. Six large pools built on top of it without checking it. They were running SPV mining: processing block headers only, skipping full block validation. The invalid chain grew 6 blocks deep before a forced reorg corrected it.\n\nThe revelation wasn't technical. It was about trust. Those six pools had signaled support for a rule they weren't enforcing. The upgrade infrastructure had been running on the honor system. It hadn't held.\n\nThe incident fed directly into 2017's SegWit debates. The case for user-activated soft forks was partly an answer to what BIP66 had exposed: miner signaling and miner readiness are not the same thing.\n\n#bitcoin #bitcoinhistory\n\nhttps://blossom.primal.net/3d9648581c2d2612b43a0713c0342e11051e298d0b437583f1850c5312baafcd.png ",
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