Ethereum Classic activated the Thanos network upgrade at block 11,700,000 on November 28, 2020, implementing ECIP-1099 to modify the mining algorithm's DAG growth schedule.
The DAG Size Problem
The Ethash mining algorithm requires miners to store a DAG (Directed Acyclic Graph) in GPU memory. The DAG grows approximately 8 MB every 30,000-block epoch (~5 days). By late 2020, the DAG was approaching the 4 GB memory limit of consumer GPUs like the GTX 1050 Ti and RX 570/580, which would force these miners offline.
ECIP-1099: Epoch Doubling
Thanos doubled the DAG epoch from 30,000 to 60,000 blocks, halving the DAG growth rate. This extended the viability of 4GB GPU mining by approximately three additional years.
Etchash Algorithm
With the epoch length change, ETC's mining algorithm is now called Etchash to distinguish it from Ethereum's Ethash. The algorithms are identical in all other respects — the only difference is the epoch duration parameter. Existing mining software required only minor configuration updates.
Mining Decentralization
The decision preserved mining accessibility for operators running consumer-grade hardware, preventing centralization toward ASIC operators and large GPU farms with 8GB+ cards. This aligns with ETC's commitment to censorship resistance through distributed mining.
Client Requirements
- Core-Geth v1.11.22 or later
- Hyperledger Besu with ETC Thanos support