Ethereum’s multi-party block construction goes live on mainnet

Ethereum blocks have traditionally been a one-builder affair. One entity assembles the transactions, one entity wins the auction, one entity gets the slot. As of September 16, that changed. Multi-party block construction, or MPBC, is now running on the Ethereum mainnet, allowing multiple builders to contribute transactions to a single block without requiring any changes to the underlying protocol. The initiative was coordinated by the Blockspace Forum, which spent much of 2026 herding an impressive coalition of block builders toward this moment. The early numbers are modest but meaningful: roughly 3% of Ethereum blocks in the first 24 hours were constructed using the multi-party approach, and more than 20,000 transactions have been included faster since testing began in late August. What MPBC actually does To understand why this matters, you need to understand how Ethereum blocks get built today. After the Merge in 2022, Ethereum adopted a system called proposer-builder separation, or PBS. Validators propose blocks, but specialized builders actually assemble them. Builders compete in an auction, and the winner’s block gets included. MPBC changes the model so that multiple builders ...