Why Bundlers Are the New Validator Set

Bundlers are the new validators. They do not just order transactions; they control the gateway to block space, deciding which user operations get included and which fail. This grants them power comparable to L1 validators but within the application layer.

The power shift is economic. Unlike L1 validators who secure the base chain, bundlers extract value from user intent. They arbitrage MEV, sponsor gas, and act as the primary interface for protocols like UniswapX and 1inch Fusion.

This creates a new attack surface. Centralization of bundling services, as seen with early dominance by entities like Pimlico and Alchemy, risks censorship and creates single points of failure for the entire ERC-4337 account abstraction stack.

Evidence: Over 90% of ERC-4337 UserOperations on mainnet are processed by just three bundler providers, a concentration of power that mirrors early Proof-of-Stake validator sets.

Bundlers control state transitions. In a rollup, validators order transactions but do not execute them. The bundler is the actor that resolves user intents into concrete on-chain transactions, directly determining the final state.

This inverts L1 governance models. Ethereum's security stems from validator consensus on execution. With intents, security depends on the economic security and liveness of the bundler network, not just chain validation.

Searcher-Builder-Proposer separation proves this. The PBS model on Ethereum shows execution (block building) accrues maximal extractable value and influence. Projects like Flashbots SUAVE and CowSwap solvers formalize this execution-layer governance.

Evidence: In Arbitrum Nova, the Data Availability Committee (DAC) controlled by Offchain Labs held unilateral upgrade power, demonstrating that execution-layer control supersedes token voting.

Bundlers control execution flow. They decide transaction ordering and inclusion, replicating the core power of L1 validators. This makes them the primary extractors of User Operation MEV.

Fee markets are now two-tiered. Users pay bundlers, who then pay L1. This creates a proposer-builder separation (PBS) dynamic where bundlers compete on efficiency, not just gas.

Censorship resistance is outsourced. Account Abstraction (AA) inherits the censorship properties of its bundler set. A decentralized network like Pimlico's bundler infrastructure is required for credible neutrality.

Evidence: The success of Flashbots SUAVE and MEV-Boost on Ethereum proves that separating block building from proposing is the dominant model. AA bundlers are the natural extension of this architecture.

Bundlers are execution validators. A mempool is a passive queue; a bundler is an active execution node. It must solve the UserOperation ordering problem, validate signatures, and simulate transactions, which requires staked capital and slashing risk, unlike a simple relay.

Economic alignment replaces passive relay. Traditional mempools rely on miner extractable value (MEV) for security. Bundlers like Pimlico and Stackup are explicitly paid via a bundler fee market, creating a sustainable, accountable service layer distinct from L1 block builders.

The validator set is permissionless. The ERC-4337 standard does not specify bundler implementation, creating a competitive market. This is analogous to the evolution from centralized RPC providers to decentralized networks like Pimlico's ERC-7677 and Alchemy's Account Kit.

Evidence: The Ethereum Foundation's ERC-4337 audit treats bundlers as a new trust assumption, requiring them to be honest for system liveness. This formalizes their role as a critical, accountable component of the chain.

Bundlers become validators. The current permissionless relay model is unsustainable for high-value transactions. Future rollups will require bonded, slashable operators to guarantee execution and censorship resistance, mirroring L1 validator economics.

Staking defines liveness. A bonded bundler network ensures transaction inclusion even during mempool congestion or MEV attacks. This creates a predictable service-level agreement that applications like UniswapX or Safe{Wallet} require for mainstream adoption.

Slashing enforces correctness. Malicious bundlers that censor, reorder for maximal extractable value (MEV), or submit invalid bundles face direct economic penalties. This aligns incentives, moving security from social consensus to cryptographic guarantees.

Evidence: The mempool is the attack surface. Flashbots' SUAVE and Ethereum's PBS roadmap prove that untrusted block building creates systemic risk. Account abstraction, with its complex intents, amplifies this, making a staked operator set a logical evolution.