Ethereum core developers and researchers kicked off Berlin Blockchain Week with an interop hacking week, dubbed Berlinterop, focused on both short-term implementation of the Fusaka upgrade and longer-term research directions. The Ethereum Foundation said the event included an all-week coworking session where devs launched fusaka-devnet-1 on day one and berlinterop-devnet-2 on day five.

During the week, developers identified changes that could not be included in a canonical fusaka-devnet-2 without consulting the public All Core Devs governance process, which is expected to happen this Thursday. Following that, devs plan to launch fusaka-devnet-2 and, in an optimistic scenario, do not expect to need a devnet-3 before moving to the Sepolia testnet around the end of the boreal summer.

The event also included a stress-testing challenge with a leaderboard, where devs earned points for breaking or hardening devnets. The Ethereum Foundation said consensus was reached on a safe immediate higher throughput level and a plan for higher levels, with details to be shared once client optimizations ensuring the safety of the 45M throughput level are released within the next week.

Long-term research

On the research side, devs discussed slot restructuring, including shortening slots and rebalancing sub-slot timings, and how proposals like ePBS, Delayed Execution, and FOCIL interact with slot structure. They also made progress on history expiry, with a blog post expected on how validators will default to dropping pre-merge history on mainnet, and identified 26 areas for consensus layer hardening.

Representatives from major L2s including Arbitrum, Base, Linea, OP Labs, Polygon, Scroll, Soneium, Starkware, World Chain, and ZKsync provided feedback on optimizing the L1-L2 relationship, focusing on more blobs, faster finality, and being kept in the loop on EVM changes. A separate ZK day with teams like RISC Zero, Succinct, and Starkware discussed the path to a zkEVM future, with consensus that it is too early to enshrine a particular ISA and that a generic RISC-V target is favored.

The Ethereum Foundation noted that interop weeks remove async-communication barriers and create contagious motivation, adding: "I'm beginning to think we really will see a 2025 Fusaka!"