Bitcoin Rollup Liveness Guarantees

No Native Settlement Guarantee. Bitcoin's consensus only secures its own chain. A rollup's sequencer can censor or halt without the L1 enforcing its progression, unlike Ethereum where L1 smart contracts can force transaction inclusion.

Operator Dependency is Fatal. Projects like BitVM or Rollkit rely on a federated or single operator to post data and fraud proofs. This reintroduces the trusted intermediary that decentralization aims to eliminate.

Compare to Ethereum's Enshrined Security. On Ethereum, rollups like Arbitrum and Optimism inherit liveness from the base layer's ability to force inclusion via contracts. Bitcoin's scripting limitations make this impossible, creating a hard security ceiling.

Evidence in Design. The BitVM whitepaper explicitly states the model requires at least one honest participant in its challenge-response protocol. This is a probabilistic, not deterministic, liveness guarantee.

Liveness over consistency: Bitcoin's Nakamoto Consensus prioritizes chain liveness, accepting temporary forks. Rollups require strong consistency for state finality, a direct architectural mismatch.

Sequencer centralization risk: A rollup sequencer on Bitcoin must wait for block confirmation (10+ minutes) before finalizing a batch. This creates a massive, uncompetitive time window vulnerable to MEV extraction and censorship.

Compare to Ethereum: Ethereum's 12-second slot time with proposer-builder separation (PBS) enables fast pre-confirmations via EigenLayer, a luxury Bitcoin's Proof-of-Work schedule denies.

Evidence: The 10-minute block target means a Bitcoin rollup sequencer operates with a 10x to 100x slower finality cadence than its Ethereum counterparts, making its liveness guarantees economically non-viable for high-frequency applications.

Bitcoin's consensus is data-agnostic. It secures a chain of hashes, not the validity of arbitrary data within transactions. A fraud proof system like Arbitrum's requires nodes to verify state transitions, a computation Bitcoin's scripting language (Script) explicitly avoids.

Fraud proofs require a judge. On Ethereum, a light client can trustlessly sync block headers and verify fraud proofs. Bitcoin has no equivalent on-chain light client protocol, forcing reliance on a centralized committee or multi-signature bridge like Multichain was.

Timelocks create liveness attacks. Even with a judge, a malicious sequencer can censor the fraud proof submission. On Ethereum, forced inclusion via EigenLayer or direct L1 calls solves this. Bitcoin's slow block time and lack of priority fee markets make censorship trivial.

Evidence: Projects like Botanix Labs and Chainway sidestep fraud proofs entirely, opting for proof-of-stake federations. This confirms the architectural mismatch; secure Bitcoin rollups today are validity-proof systems or trusted multisigs.

Probabilistic finality is sufficient. Bitcoin rollups like BitVM and Citrea rely on a small, honest minority of watchers to challenge invalid state transitions. This creates a liveness guarantee that is high-probability, not absolute, which mirrors the security model of Bitcoin's proof-of-work itself.

The alternative is stagnation. The Nakamoto consensus bottleneck is the root constraint. Demanding absolute, instant liveness on a base layer that finalizes every 10 minutes is architecturally impossible. The pragmatic choice is a fraud-proof window (e.g., 7 days) that provides ample time for intervention.

Compare to optimistic rollups. This model is battle-tested. Arbitrum and Optimism secured tens of billions with a 7-day challenge period. The key difference is the data availability guarantee, which for Bitcoin rollups is the immutable Bitcoin blockchain, a superior foundation.

Evidence: The Lightning Network operates on a similar principle—it's a probabilistic payment channel network secured by the threat of on-chain settlement. Its success demonstrates that sufficient liveness for a use case, not perfection, drives adoption.

Liveness is non-negotiable. A Bitcoin rollup that cannot force-include transactions is a custodial sidechain. The sequencer's ability to censor directly threatens user sovereignty and capital efficiency, as assets remain locked.

Bitcoin's consensus is the ultimate arbiter. Unlike Ethereum's social consensus for L2s, Bitcoin's unforgeable timestamps and block ordering provide a deterministic, on-chain mechanism for resolving disputes and ensuring state progression.

Soft forks enable hard guarantees. Proposals like OP_CHECKTEMPLATEVERIFY (CTV) and BitVM create covenants that enforce honest sequencer behavior. These are trust-minimized escape hatches for users, not just optimistic promises.

Compare to Ethereum's model. Ethereum rollups rely on a social layer and multi-sigs for upgrades and emergency exits. Bitcoin's approach is cryptoeconomic and automated, removing human committees from the liveness equation.

Evidence: The 10-block challenge. A functional Bitcoin rollup must allow any user to force-include a state transition within a fixed number of Bitcoin blocks, typically 10-20, making censorship economically irrational.