Multi-Party Block Construction (MPBC) has officially launched on the Ethereum mainnet, a development coordinated by the Blockspace Forum. This new system allows multiple builders to contribute transactions to a single block, aiming to enhance network efficiency and reduce centralization in block production.
In the first 24 hours following its activation on September 16, approximately 3% of Ethereum blocks were constructed using the MPBC approach. Since testing commenced in late August, over 20,000 transactions have been included at an accelerated rate. Early data indicates that some multi-party blocks have incorporated up to 810 additional transactions compared to blocks built by a single entity. In certain instances, gas usage has seen a significant increase, jumping nearly 14-fold.
Context: The Evolution of Block Construction
Prior to MPBC, Ethereum’s block construction largely operated on a single-builder model. Following the adoption of Proposer-Builder Separation (PBS) after the Merge in 2022, validators propose blocks while specialized builders assemble them. Builders compete in an auction, and the winner’s block is included in the chain. This model, however, allowed a single builder to control transaction ordering within a block, potentially leading to prioritization of certain transactions over others.
MPBC: A Shift in Dynamics
MPBC introduces a fundamental shift by enabling multiple builders to contribute to the creation of a single block. This creates multiple inclusion paths, rather than funneling all transactions through one entity. The design of MPBC is strictly additive, meaning it does not require protocol changes, hard forks, or consensus-level modifications. The system operates at the builder and operator layer and does not depend on relays for its core functionality.
The Blockspace Forum has been instrumental in coordinating this initiative, holding workshops throughout 2026, including a meeting in Cannes attended by 32 teams. These teams represent over 95% of out-of-protocol block contributions on Ethereum. Foundational research outlining MPBC design principles was published in May 2026.
The implementation of MPBC aims to dilute the control that single entities have over transaction ordering and inclusion. While it does not eliminate these dynamics entirely, it distributes the influence across multiple builders. This approach can lead to fuller blocks, greater transaction diversity, and faster confirmation times for pending transactions, as service transactions gain additional pathways into blocks without competing solely within a single builder’s priority queue.
Public documentation and a live dashboard for MPBC metrics have been released, providing transparency into the system’s operation. The current PBS model, where a single builder wins each auction, has structural issues that can compound over time. MPBC addresses this by introducing a parallel path that reduces chokepoint risks associated with a single point of control.
Why This Matters
The materials describe a narrow update: Multi-party block construction (MPBC) is now live on the Ethereum mainnet, allowing multiple builders to contribute transactions to a single block without protocol changes. MPBC changes the model so that multiple builders can each contribute transactions to a single block, creating multiple inclusion paths rather than funneling everything through one entity.
Broader Context
Source materials place the factual news in this context: Ethereum blocks have traditionally been a one-builder affair.
