Role of Non-Finality Testing in the Fusaka Upgrade

Non-finality testing is presented as one of the most critical pre-fork validation processes for Ethereum's Fusaka upgrade, simulating unstable network conditions to uncover client-specific vulnerabilities and validate recovery. The Fusaka Devnet-3 non-finality tests, led by Nico Flaig, use three phases: validator outages that push participation below 66%, bandwidth throttling of about 30% of validators to 1 Mbps, and network splits and merges. The article says these tests will shape client readiness for September's Holesky and Sepolia forks and precede the targeted November 5, 2025 mainnet launch.