Off-chain relayers—entities that collect, order, and forward transactions to block producers—can concentrate power in the transaction pipeline, but whether they erase on-chain decentralization over time depends on incentives, design, and countermeasures. Research shows that private transaction channels enable extractive behaviors that shift where power resides without necessarily changing on-chain consensus rules. Philip Daian, Cornell University identified how private relays and searcher economies create outsized advantages for parties that control ordering, a phenomenon described as Miner Extractable Value and later generalized as Maximal Extractable Value. Vitalik Buterin, Ethereum Foundation has proposed structural changes like proposer-builder separation to rebalance incentives and reduce centralized builder power.
How relayers can centralize ordering
Off-chain relayers reduce latency and enable complex matching, attracting sophisticated searchers and large builders. Over time this leads to a small set of builders capturing the majority of block construction opportunities because they can offer higher payments and faster execution. The effect is a shift from many independent mempool participants to fewer, specialized intermediaries. This concentration creates single points where censorship, collusion, or policy pressure can be applied. Not every relay becomes dominant, and market competition can limit consolidation, but economic rents favor aggregation.
Consequences and contextual nuances
Centralized relays can undermine practical decentralization by making validators dependent on a handful of builders for revenue and well-formed blocks. That dependence increases systemic risks: censorship of transactions, coordinated reordering, and barriers for geographically or economically marginalized participants to participate fully. Human and territorial dimensions matter because relayer operators and data centers often cluster in regions with reliable infrastructure and capital; that clustering raises legal exposure and potential regulatory coercion from local authorities. Environmental implications are indirect: centralized services may optimize for throughput in ways that change hardware and energy demands, concentrating infrastructure and supply chains.
Mitigations exist and are being actively researched. Protocol-level responses like proposer-builder separation advocated by Vitalik Buterin, Ethereum Foundation, transparent public relays, and open-builder incentives reduce single-point power. Community and engineering measures promoted by projects following the findings of Philip Daian, Cornell University and others aim to preserve on-chain rule-making while keeping off-chain innovation. In short, off-chain relayers create a real centralization pressure, but design choices and governance can limit long-term erosion of on-chain decentralization. The balance depends on how communities align incentives, build transparent tooling, and enforce open access.