At block 200,000 on September 7, 2015, the Frontier Thawing upgrade removed the initial 5,000 gas limit that had been in place since genesis, enabling miners to vote on gas limit increases.
What Changed
The Frontier genesis launch deliberately set a 5,000 gas per block limit — enough for simple ETH transfers but too low for meaningful smart contract execution. Frontier Thawing unlocked this limit and set the default target to 3,141,592 gas per block, allowing miners to adjust the limit through the standard voting mechanism.
Difficulty Bomb Introduced
Frontier Thawing also introduced the exponential difficulty bomb — a mechanism that progressively increases mining difficulty to make block production impractical. The bomb was designed to force future protocol upgrades by making the chain unusable without them.
Ethereum Classic later removed the difficulty bomb permanently at block 5,900,000 (ECIP-1041), affirming its commitment to proof-of-work consensus. Ethereum delayed the bomb five times before transitioning to proof-of-stake in September 2022.
Significance
This upgrade marked the moment smart contract deployment became practical on the network. The blockchain that Ethereum Classic continues today first became a usable smart contract platform at this block.