Crypto

Ethereum Rebuilt Its Block Factory So More Builders Can Share Each Block

By Omar aka Crypt0 · Sep 17, 2026

Ethereum shipped an upgrade this week that changes how every block gets built, and almost every user will experience it working silently. Multi party block construction, or MPBC, went live on mainnet September 16, letting multiple builders contribute transactions to a single block for the first time. The block auction stays exactly as it was. The construction crew just got bigger and more open. For readers, the payoff is subtle and durable: fairer ordering and stronger inclusion guarantees in every block you interact with.

Under Ethereum's existing proposer builder separation, builders assemble complete blocks and compete to have validators select theirs. MPBC extends that architecture with an append only model: one builder creates the initial block, and additional builders can append eligible transactions before the block reaches the proposer. The crucial detail is that appended contributions leave the initial transactions untouched. One builder's block becomes a shared canvas, open to many contributors.

The rollout arrived with serious infrastructure behind it. The Blockspace Forum, which stewarded the deployment, lists participants including Titan Builder, Ultra Sound, Bomba, Quasar, ETH Gas, NasdaqBTCS, Kraken, Kiln, Blockdaemon, Lido, Puffer, and SSV Network, and published an open source reference implementation for anyone wanting to join. More than 85 percent of the transaction pipeline and more than 90 percent of connected validators supported the initial deployment. Wallets, decentralized apps, and layer 2 networks continue exactly as before. The open reference implementation means smaller builders can join from day one rather than rebuilding the stack themselves.

The design carries a quiet superpower: censorship resistance by construction. Under the old model, a transaction generally needed the winning builder to include it. With MPBC, a transaction that one builder leaves out can be picked up by another participating builder within the same block. Inclusion gets a second chance as a built in protocol feature. The system is also being built with compatibility in mind for enshrined proposer builder separation and the proposed FOCIL mechanism, so this layer keeps compounding.

This is Ethereum doing what it does best: decentralizing the machinery that runs beneath the surface. Block building had been consolidating into fewer hands, and MPBC answers by widening the door instead of picking a champion. The network's plumbing now resists capture one block at a time, and every user benefits automatically.

The beauty of this upgrade is its invisibility. Everything on the surface continues exactly as before, while the machinery underneath grows steadily harder to capture. The most meaningful decentralization happens in the layers that simply work.

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