In Ethereum MEV relay networks, the amounts paid as priority fees are proposed by the party trying to capture value, typically the searchers, while the final acceptance and collection depend on relays and validators. This division of roles shapes who effectively sets and enforces the economic priority delivered to block producers.
Roles and who proposes fees
Searchers construct transaction bundles that bundle MEV-extracting trades and include a priority fee (a tip) intended for the validator. Flashbots team at Flashbots explains that relays exist to privately forward those bundles to validators rather than broadcasting them on-chain, allowing searchers to signal tips off-chain. Vitalik Buterin at the Ethereum Foundation clarified the fee-market distinction introduced by EIP-1559, where base fees are protocol-determined but tips remain discretionary and are set by transaction proposers or searchers.
Who enforces acceptance
Although searchers propose the amount, validators ultimately set which bundles they include by accepting or rejecting them. Relays implement policies and admission controls — for example minimum tip thresholds or whitelists — so relays can effectively influence which priority fees are surfaced to validators. Dan Robinson at Paradigm and the Flashbots team at Flashbots have analyzed how relay policies and validator-configured acceptance rules together determine which proposed priority fees translate into real payments.
This arrangement has clear relevance: the separation of proposal and acceptance creates strategic behavior. Searchers compete by increasing tips and optimizing bundle content, relays curate and filter traffic, and validators balance revenue against consensus, censorship, or decentralization concerns. The causes stem from transaction-order-dependent profit opportunities (MEV) and Ethereum’s fee design that leaves tips as a flexible lever.
Consequences include incentives for centralization and specialized tooling. When only a few relays or large searcher firms dominate, ordinary users face higher front-running risk and potential exclusion, impacting market fairness and the cultural norms of permissionless finance. On the technical and environmental side, competitive searcher activity increases off-chain computational work and network messaging, though Ethereum’s move to proof-of-stake reduces the protocol’s energy footprint relative to proof-of-work.
Understanding who effectively sets priority fees requires seeing the whole pipeline: searchers propose fees, relays shape which proposals reach block builders, and validators exercise final acceptance — a three-way interaction documented by the Flashbots team at Flashbots, analyzed by Dan Robinson at Paradigm, and situated within Ethereum’s fee framework by Vitalik Buterin at the Ethereum Foundation. Policy choices by relays and validators can therefore change market dynamics as much as searcher strategies do.