Ethereum has deployed multi-party block construction (MPBC) on the mainnet, enabling multiple builders to contribute transactions to a single block.

The first production implementation of MPBC went live on September 16, 2026, with ongoing work to publish additional specifications, live data, and documentation as development continues.

An open‑source reference implementation for MPBC is available for infrastructure providers, and development will continue to expand specifications, documentation, and live data as rollout progresses.

The current PBS auction mechanism remains unchanged; MPBC operates at the block-construction layer and does not create a separate validator auction.

Early adoption appears strong, with over 90% of connected validators and more than 85% of the transaction pipeline reportedly supporting the rollout.

MPBC builds on proposer-builder separation (PBS) by enabling an append‑only model where initial block content can be augmented by additional builders before finalization by the proposer.

MPBC could alter transaction competition and censorship-resistance, as extra builders may add transactions excluded by others, depending on participation levels.

MPBC is part of broader Ethereum infrastructure efforts and is distinct from projects like Lido’s ValOS or Aave V4, which address validator operations and DeFi infrastructure, respectively.

Infrastructure providers such as Aestus, Titan, and Ultra Sound are participating in MPBC, coordinating inputs from different builders before blocks proceed through the standard transaction pipeline.

End users—wallets, DApps, and Layer 2 networks—do not need to change how they submit transactions, as MPBC operates at the block-construction layer and remains largely transparent.