Why Rollup-to-Rollup Bridges Will Centralize If We're Not Careful

Shared sequencing is centralization. The dominant interoperability model for rollups like Arbitrum and Optimism relies on a shared sequencer or a canonical bridge. This creates a single point of failure for cross-rollup liquidity and composability, directly contradicting the modular goal of fault isolation.

Liquidity follows the path of least resistance. Projects like Stargate and LayerZero build canonical bridges that become the default. This creates winner-take-most network effects, where the dominant bridge's security assumptions become the de facto standard for the entire ecosystem.

The validator set is the attack surface. A bridge like Across or a shared sequencer operated by a consortium like Espresso or Astria centralizes trust. If that entity is compromised or coerced, the cross-rollup state is corrupted, making isolated rollup security irrelevant.

Evidence: The TVL and transaction flow for Arbitrum's canonical bridge dwarfs all third-party alternatives. This creates a systemic risk where the economic activity of dozens of rollups depends on the liveness of a handful of entities.

Winner-take-all liquidity concentrates in the bridge with the deepest pools and lowest latency. This creates a liquidity moat where protocols like Across and Stargate become the default, forcing smaller bridges to exit the market.

Centralized sequencing is the logical endpoint. Bridges that batch and route transactions, like LayerZero's Executor or Connext's routers, become de facto centralized sequencers for cross-chain state, creating a single point of failure and censorship.

The validator cartel problem emerges. To secure fast, trust-minimized bridges, protocols rely on a small set of bonded validators, replicating the Proof-of-Stake centralization they were built to escape. This is evident in the staking models of Axelar and Wormhole.

Evidence: The top three bridges by volume—Stargate, Across, LayerZero—control over 60% of all cross-chain liquidity. This mirrors the centralization seen in CEX order books, where the top three exchanges dominate 90% of spot trading.

Liquidity centralizes at hubs. Rollup-to-rollup bridges like Across and Stargate pool liquidity in a central vault on a single chain. This creates a single point of failure and forces all economic activity through a privileged hub, mirroring the financial system we aimed to escape.

Security models are custodial. Most bridges rely on a multi-sig or MPC committee for validation. This is a trusted third party, not a decentralized verifier. The security of billions in bridged assets depends on a handful of entities.

The winning bridge captures all. Network effects in liquidity and user trust create a winner-take-most market. This centralizes protocol development and fee extraction, stifling the permissionless innovation that defines rollups.

Evidence: Over 70% of cross-rollup volume flows through the top three bridge protocols. Their security councils, like those for Arbitrum and Optimism native bridges, control upgrade keys for hundreds of millions in TVL.

Liquidity centralization is inevitable. Native bridges like Arbitrum's and Optimism's already dominate because they are subsidized by sequencer revenue and offer instant guaranteed finality. Competing third-party bridges like Across or Stargate cannot match this without forming centralized liquidity cartels.

The trust model regresses. A secure bridge needs a decentralized set of attestors. For speed, bridges will rely on the rollup's single sequencer for attestation, creating a single point of failure and control. This is the permissioned model of Celestia's Blobstream, not a permissionless validator set.

Cross-chain MEV demands centralization. To capture atomic arbitrage across rollups, bridge operators must control transaction ordering on both sides. This requires becoming a validator or forming exclusive partnerships with sequencers, a dynamic already visible in LayerZero's off-chain executor network.

Evidence: Sequencer as Sole Attestor. Today, withdrawing from Arbitrum to Ethereum relies solely on the Arbitrum sequencer's state attestation. This centralized trust model is the blueprint for fast rollup-to-rollup bridges, not the exception.

Light clients require data availability. A rollup's light client needs the source chain's block headers to verify state. If the source is another rollup, you now need a trusted data availability layer for those headers, creating a recursive trust problem.

ZKPs shift, not eliminate, trust. A ZK proof of state transition is only as good as its inputs. You still need a trusted data feed to provide the proven state root, which is the same centralization vector for protocols like LayerZero.

Economic centralization is inevitable. The cost to run a verifier node for a ZK light client bridge between two rollups is high. This creates a professional validator class, mirroring the centralization of current sequencer sets.

Evidence: The canonical bridge from Arbitrum to Optimism is a multi-sig. The Across and Stargate bridges use off-chain relayers. No major production system uses a pure ZK light client for rollup-to-rollup communication today.

Native bridging centralizes sequencers. When a rollup's native bridge is the primary liquidity path, its sequencer becomes a single point of censorship and failure. This architecture mirrors the early days of Binance Smart Chain, where a single entity controlled the canonical bridge.

Liquidity fragmentation creates monopolies. Without a standardized messaging layer, each bridge (e.g., Across, Stargate) must bootstrap its own liquidity pools. This leads to winner-take-most dynamics where the first-mover captures all volume and dictates fees.

Intent-based systems are not a panacea. Protocols like UniswapX and CowSwap abstract bridging through solvers, but they outsource trust to solver networks. These networks will consolidate, creating a new cartel of centralized intermediaries.

Evidence: LayerZero's initial design relied on a single Oracle and Relayer, a flaw exploited in the Stargate hack. The subsequent push for the Omnichain Fungible Token (OFT) standard is a direct response to this centralization risk.