Multi-party block construction (MPBC) is now live on Ethereum mainnet, allowing multiple builders to contribute transactions to one block through an append-only design. One builder creates the initial block, while others can add eligible transactions before it reaches the proposer; existing transactions cannot be altered. The system extends Ethereum’s proposer-builder separation (PBS) without changing the established auction through which proposers select blocks. About 3% of blocks used MPBC during its first 24 hours, while more than 20,000 transactions have been included faster since testing began in late August. Some blocks included up to 810 additional transactions, and gas usage in certain cases rose nearly 14-fold. Aestus, Titan and Ultra Sound are among the infrastructure providers supporting the rollout, while more than 85% of the connected transaction pipeline and over 90% of connected validators supported the initial deployment. The figures apply to infrastructure connected to MPBC, not all Ethereum validators. Wallets, decentralized applications and Layer 2 networks do not need to change how they submit transactions. The Blockspace Forum plans to publish further specifications, documentation and live data as the system develops, including work toward compatibility with enshrined proposer-builder separation and FOCIL.