Ethereum Classic (ETC) is the native cryptocurrency of Ethereum Classic, a proof-of-work blockchain that continues the original Ethereum transaction history without the 2016 reversal of the DAO hack. ETC pays transaction fees, rewards miners who secure the network, and runs smart contracts written for the Ethereum Virtual Machine. Its total supply is limited to about 210.7 million ETC.
ETC should not be confused with Ethereum (ETH), the coin of the much larger chain that adopted the 2016 fork and later moved to proof of stake. The two chains share their first 1.92 million blocks but have run separately ever since; see the Ethereum Blockchain for the other branch.
Ethereum Classic in plain terms
Picture a club whose rule book says that whatever the club's vending machine does is final. One day someone finds a flaw in the machine and drains a large share of the members' money. Most members vote to rewind the machine's records and give the money back. A minority refuse: they say the rule book is the rule book, and that rewinding history once makes it possible to do it again.
The club splits in two. The majority keep the old name with the rewound records, and the minority carry on with the original, untouched records under a new name: Ethereum Classic. ETC is the money of that second club, and its members still see "the code is the law" as the point of the whole system.
History
Ethereum launched in July 2015. In June 2016 an attacker exploited a flaw in The DAO, a decentralized autonomous organization that had raised more than 11 million ETH, and used a hack of its code to move roughly 3.6 million ETH out of it. In July 2016, at block 1,920,000, the Ethereum community adopted a hard fork that returned the funds. Miners and users who rejected it kept the unaltered chain running, arguing that the network should never overrule the outcome of its own code. Within days the exchange Poloniex listed the coin of the original chain as ETC, and other exchanges followed. In 2017 the community adopted a capped supply. When Ethereum switched to proof of stake in September 2022, Ethereum Classic became the largest smart-contract network still secured by mining, and many former Ethereum miners moved to it.
How it works and its fixed supply
New blocks are mined with Etchash, a variant of Ethereum's original mining algorithm adopted in late 2020. Instead of Bitcoin's halving, ETC follows a schedule set by the improvement proposal ECIP-1017, often called "5M20": the block reward falls by 20 percent every 5 million blocks, about every two years. The reward per block is:
- is the block reward in ETC during era .
- counts completed 5-million-block eras, starting at 0 for the first 5 million blocks.
- reflects the 20 percent cut at each new era.
The reward was 5 ETC at the start, 3.2 ETC from block 10 million in March 2020, and 2.048 ETC after block 20 million in May 2024. At block 25,000,001, and the reward is ETC, the level that applies from that block, which the chain was expected to reach around mid-2026. Because each era pays less than the one before, total issuance approaches a ceiling of about 210.7 million ETC, a similar idea to Bitcoin's 21 million cap.
Security and the 51% attacks
Because ETC's mining power has been much smaller than that of larger proof-of-work chains, renting enough hardware to control it has been relatively cheap. In January 2019 the exchange Coinbase detected deep chain reorganizations in which an attacker double-spent about 219,500 ETC, worth around $1.1 million. In August 2020 the chain suffered three 51% attacks in one month; the first rewrote more than 3,600 blocks and was used to double-spend about 807,000 ETC, roughly $5.6 million, through deposits at the exchange OKEx. The attacks led some exchanges to require far more confirmations for ETC deposits and to threaten delisting. Developers responded later in 2020 with a scoring rule that makes deep reorganizations harder and with the switch to Etchash, intended to separate ETC's miners from Ethereum's.
Uses and criticism
ETC is used to pay fees, to reward miners and to run Ethereum-compatible applications, and it trades on most centralized exchanges. Supporters value its fixed supply, its refusal to reverse transactions, which they see as protecting immutability, and its continued use of mining. Critics point out that it has far fewer developers, users and applications than Ethereum, that its history of attacks shows the weakness of a smaller proof-of-work network, and that much of its trading is speculative rather than tied to real use. Mining also concentrates power in a handful of large pools, so a few operators produce most blocks at any given time.