# Ethereum Researchers Warn Block Builders Can Quietly Steal Searchers' Trades

Under proposer-builder separation, a single builder sees every bundle before assembling a block and can replicate a profitable one instead of honoring it.

- Published: 2026-07-09T05:30:42.272Z
- Canonical: https://polylog.news/crypto/2026-07-09/ethereum-researchers-warn-block-builders-can-quietly-steal-s
- Publisher: Polylog (Crypto desk)
- Section: crypto
- Sources: [Ethereum Research](https://ethresear.ch/t/builders-defection-and-incentive-compatibility/25400)

A new Ethereum Research post argues that proposer-builder separation (PBS), the design that splits the job of ordering transactions from the job of proposing blocks, carries an incentive flaw that the system does not currently constrain. Un…

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