Core Development Timeline

Ethereum Classic genesis. The original Ethereum codebase launches — the first production EVM with smart contract capability. The ledger begins.

Gas limit raised from 5,000 to allow network growth. Mining difficulty threshold adjusted.

First major planned upgrade. Removed the provisional Frontier protective measures; the network transitions from beta to a stable production platform.

Gas cost repricing for IO-heavy operations to prevent denial-of-service attacks that had been exploiting underpriced opcodes.

Delayed the difficulty bomb and implemented replay protection via chain ID. ETC's chain ID 61 derives from its coin_type value in the BIP44 derivation path (m/44'/61'/0'/0/index). ETC's first independent protocol deviation from Ethereum.

Established ETC's fixed monetary policy: the 5M20 era system with a 210,700,000 maximum supply. Block rewards reduce 20% — a fifthening — every 5,000,000 blocks, roughly every two years. Inspired by Bitcoin's halving schedule but designed to soften the miner hardware shock and spot price dislocation a 50% supply cut produces: the gradual reduction preserves the same long-term predictability with a smoother transition at each era boundary.

Permanently removed the difficulty bomb — the artificial mechanism designed to pressure migration to Proof-of-Stake. With the bomb gone, Ethereum Classic became the canonical long-term Proof-of-Work EVM, establishing the two-EVM model: a flagship PoS chain and a flagship PoW chain, each with distinct security properties and trust assumptions, both sharing the EVM execution standard.

Byzantium parity. Added precompiles for elliptic curve arithmetic enabling ZK-proof compatibility, REVERT opcode, and receipt status codes.

Constantinople and Petersburg parity. Introduced bitwise shifting opcodes, CREATE2 for deterministic contract deployment, and EXTCODEHASH.

Istanbul parity. Added BLAKE2 precompile, repriced elliptic curve operations, chain ID opcode, and improved gas cost accuracy for storage operations.

Introduced ETChash — a modified DAG growth algorithm keeping ETC mineable on GPU hardware — and MESS (Modified Exponential Subjective Scoring) for chain finality. Following Ethereum's Merge, ETC absorbed a significant portion of the global GPU mining network and every purpose-built Ethash ASIC miner — the only chain still running an ETChash-compatible algorithm.

Berlin parity. Repriced cold storage access operations, introduced typed transaction envelopes, and added optional access lists for gas optimization.

Partial London parity — gas refunds reduced, 0xEF bytecode prefix reserved — without EIP-1559. The fee market was deliberately deferred to gather empirical data on adoption and gas dynamics, and to resolve where the basefee should flow: burned as on Ethereum, or redirected to a protocol treasury. The 2021 developer consensus landed on the treasury model, a position formalized four years later with the Olympia upgrade.

Partial Shanghai parity, excluding Proof-of-Stake validator withdrawals not applicable to Ethereum Classic. Warm COINBASE access, PUSH0 opcode, and initcode size limit. Remaining Shanghai gaps are filled by the Olympia upgrade.