Ethereum Classic · 2016
The block where Ethereum became two histories
At block 1,920,000, operators faced a decision that the code could implement but could never make for them.
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On 20 July 2016, Vitalik Buterin posted a short report on the Ethereum Foundation blog. A change had taken effect at block 1,920,000. Roughly twelve million ether held in contracts associated with The DAO had been moved into a recovery contract. People entitled to recover funds could begin claiming them. On the chain running that software, the intervention was already an observable fact.
Near the end of the report was an instruction for readers who disagreed. They could run a client configured to oppose the fork. That detail captures the stakes better than the word “upgrade” does. An operator could accept a one-time change to the ledger after The DAO exploit, or continue validating transactions under the earlier rules. Enough participants chose each path for both histories to survive. The latter network became known as Ethereum Classic.
For a holder at the time, this was more than a philosophical distinction. Buterin warned about replay: a signed transaction intended for one branch could also be accepted on the other. The communities could disagree about which ledger to follow while the software still recognised the same signature. Today the Ethereum guide and the Ethereum Classic guide describe separate assets. For their earliest blocks, the two guides share a history.