Multi-party block construction (MPBC) is now live on the Ethereum mainnet as of September 16, 2026. This system allows multiple builders to contribute transactions to a single block, moving away from the traditional model where one entity controls the entire block assembly process.
The initiative was coordinated by the Blockspace Forum, which organized workshops throughout 2026, including a meeting in Cannes with 32 teams representing over 95% of out-of-protocol block contributions. The design principles were established in research published in May 2026.
MPBC operates at the builder and operator layer without requiring protocol changes, hard forks, or consensus-level modifications. It functions independently of relays, creating a parallel path that reduces chokepoint risks and dilutes the control of a single builder over transaction ordering.
Early data from the first 24 hours shows that approximately 3% of Ethereum blocks were created using the multi-party approach. Since testing began in late August, over 20,000 transactions have been included faster, with some blocks containing up to 810 additional transactions and gas usage increasing nearly 14-fold.
