Why Bundler Censorship is Inevitable

Bundlers are profit-maximizing entities. Censorship is not a bug but a feature of their revenue model. They will naturally exclude transactions that threaten their extractable value or align with blacklists.

• Profit Motive: Blocking transactions that enable competing MEV searchers or arbitrage opportunities is rational.
• Regulatory Pressure: Compliance with OFAC sanctions becomes trivial when you control transaction ordering, creating a centralized choke point.
• Network Effect: Dominant bundlers like those in the Ethereum PBS ecosystem set de facto standards for what gets included.

In intent-based systems (e.g., UniswapX, CowSwap), the solver/bundler is the liquidity gateway. Whoever controls the bundler controls market access.

• Vertical Integration: Bundlers affiliated with specific DEXs or L2s will prioritize their own liquidity, censoring routes to competitors.
• Cross-Chain Control: Bridges like LayerZero and Across rely on relayers—a form of bundler—creating censorship risk for entire asset flows.
• User Lock-in: Protocols become dependent on a few bundled liquidity sources, losing sovereignty over their own transaction flow.

Bundler infrastructure is highly centralized, running on AWS, Google Cloud, and other censorable services. The software stack itself creates single points of failure.

• RPC Reliance: Most bundlers use a handful of centralized RPC providers (e.g., Alchemy, Infura), which can filter transactions upstream.
• Fast Finality Trade-off: To achieve ~500ms latency, bundlers must make centralized, pre-confirmation decisions, which are inherently censorable.
• Opaque Logic: The proprietary matching engines in solvers and bundlers are black boxes, making detection of subtle censorship nearly impossible.

The only credible mitigation is to bake credibly neutral transaction ordering into the protocol layer itself.

• L1 PBS: Ethereum's roadmap aims to enshrine PBS, separating block building from proposing, but builder centralization remains a risk.
• L2 Enshrined Sequencers: Rollups like Fuel and Espresso are exploring decentralized, shared sequencer sets to prevent single-operator censorship.
• Force Inclusion Lists: Protocols like Arbitrum have mechanisms to bypass sequencers, but they are slow and costly, a last resort.
• Sovereign Rollups: By posting data to Celestia or EigenDA and letting anyone produce blocks, they eliminate the dedicated bundler role entirely.

If bundlers are unavoidable, the system must be designed to punish censorship through economic slashing and competitive routing.

• SUAVE: Aims to create a decentralized block builder marketplace, but its own sequencer set could become centralized.
• Reputation-Based Routing: Users/clients could route intents based on a bundler's historical censorship score, creating a market for neutrality.
• Staked Bonding: Requiring bundlers to post slashable bonds for liveness and censorship resistance, similar to EigenLayer restaking for AVSs.
• Multi-Bundler Clients: Wallets and protocols must integrate multiple bundlers and RPCs, forcing competition on inclusion, not just price.

Reduce bundler discretion by making user intents explicit, verifiable, and executable by any compliant party.

• Standardized Intents: Define a common schema (e.g., ERC-7521) so intent fulfillment is a verifiable computation, not a discretionary service.
• Open Solver Networks: Create open auctions for intent fulfillment where any solver can participate, breaking bundler monopolies. CowSwap's CoW Protocol is a model.
• User-Signed Constraints: Allow users to attach specific requirements (e.g., "must not use these OFAC addresses") that are cryptographically verifiable, making censorship detectable.
• Fully On-Chain Auctions: Move the bundler auction on-chain with programmable rules, as explored by Astria and Radius.

Bundlers are just specialized block builders. Their profit is derived from maximal extractable value (MEV), not just base fees. This creates an inherent conflict: a user's transaction can be censored if it threatens a more profitable MEV opportunity for the bundler or its searcher partners.

• Economic Inevitability: Profit-maximizing bundlers will always prioritize the most valuable bundle.
• Centralization Pressure: Only large, well-capitalized entities can compete for top-of-block positioning, leading to oligopoly.

Bundlers are identifiable, on-chain entities with clear fiat off-ramps. This makes them low-hanging fruit for regulators enforcing sanctions lists (e.g., OFAC). Compliance is not optional for sustainable businesses.

• De Facto Censorship: Compliance-driven bundlers will filter sanctioned addresses, fragmenting the mempool.
• Legal Precedent: The Tornado Cash sanctions set the template; bundlers are the next logical enforcement target.

Simply having a permissionless bundler set doesn't prevent censorship. The economic and latency advantages of professional bundlers are insurmountable for hobbyists.

• Stake & Latency Arms Race: Winning the auction requires high-performance infrastructure and significant stake (e.g., EigenLayer AVS), creating barriers.
• Solution Path: Censorship resistance must be engineered at the protocol level via mechanisms like proposer-builder separation (PBS) and inclusion lists, not assumed from decentralization.