Force Inclusion

Force Inclusion is a protocol-level guarantee in optimistic rollups and validiums that allows users to directly submit their transaction data to the underlying Layer 1 (L1) blockchain, such as Ethereum, if the rollup's designated sequencer fails to do so within a predefined time window. This mechanism acts as an economic and cryptographic escape hatch, ensuring that users can always withdraw their assets or prove their state transitions, even if the rollup operator is malicious or offline. It is a foundational component of the trust-minimized security model for Layer 2 solutions.

The process is typically triggered when a user submits a force inclusion transaction or a data availability request directly to a smart contract on the L1. This contract verifies the request's validity—often requiring a cryptographic proof or a challenge period—and then compels the rollup's state to process the transaction. This ensures data availability, a prerequisite for anyone in the network to reconstruct the rollup's state and verify correctness. Without force inclusion, users could be indefinitely censored by a sequencer, locking their funds in the L2.

A key distinction exists between its implementation in optimistic rollups versus validiums. In an optimistic rollup like Arbitrum, force inclusion ensures transaction data is posted to L1, allowing watchers to build fraud proofs. In a validium like StarkEx, it ensures data availability certificates (DA proofs) are published, enabling the generation of validity proofs. In both cases, the mechanism enforces a service-level agreement (SLA) on the sequencer, making censorship economically non-viable and preserving the self-custodial properties of the underlying blockchain.

Force inclusion is a protocol-level guarantee that allows a user to directly submit a transaction's data to the Layer 1 (L1) blockchain if a rollup's sequencer fails to process it within a predefined time window. This mechanism is the user's ultimate recourse against a malicious or malfunctioning sequencer that might censor transactions or become unavailable. By bypassing the sequencer, force inclusion ensures that the rollup's state can still be advanced and that user funds remain accessible, preserving the system's core security properties derived from the L1.

The process typically involves the user submitting a transaction with its full calldata to a special contract on the L1, often called the Inbox or Sequencer Inbox. This contract verifies that the sequencer has exceeded the allowed delay—commonly several hours to a day—for including the transaction. Once verified, the data is permanently recorded on-chain. Validators or provers for the rollup are then obligated to incorporate this force-included data into the next state update, ensuring the transaction's effects are reflected in the rollup's state.

This mechanism is a foundational component for censorship resistance in optimistic and zero-knowledge rollups. Without it, a sequencer could theoretically freeze user assets indefinitely. Force inclusion aligns with the Ethereum roadmap's concept of enshrined rollups, where certain functions are baked into the protocol for stronger guarantees. It represents a key difference from sidechains, which lack this type of enforceable bridge to the settlement layer, and is crucial for maintaining the trust-minimized and permissionless nature of rollup ecosystems.

Force inclusion is a protocol-level mechanism that guarantees a transaction will be included in a future block, overriding a block producer's ability to censor or indefinitely delay it. This is achieved by allowing a user to submit a transaction with a special flag or by invoking a specific smart contract function, which creates a cryptographic commitment that subsequent validators are obligated to honor. The mechanism acts as a countermeasure against Maximal Extractable Value (MEV) extraction and censorship, ensuring network liveness and fairness even when block space is contested.

The technical implementation typically involves two phases: a commit and a reveal. First, a hashed version of the transaction (the commitment) is submitted on-chain, often with a bond or fee. After a predetermined number of blocks, the original transaction data is revealed. Validators for subsequent blocks are then compelled by protocol rules to include the revealed transaction, often prioritizing it over others in the mempool. This design prevents front-running, as the transaction's full details are hidden during the commitment phase.

A prominent example is Ethereum's block.blobbasefee and EIP-4844 blobs, where force inclusion rules ensure data blobs are published within a specific time window. Another implementation is found in Flashbots' SUAVE chain, where force inclusion is a native primitive for fair transaction ordering. The mechanism's security relies on cryptoeconomic incentives: validators who fail to include a force-included transaction are subject to slashing penalties or miss out on guaranteed fee revenue, making censorship economically irrational.

From a system design perspective, force inclusion introduces trade-offs. It can complicate block construction logic and potentially reduce a validator's flexibility in optimizing block revenue from MEV. Therefore, parameters like the force inclusion delay and fee premium must be carefully calibrated. These parameters balance user urgency against validator autonomy, ensuring the mechanism is used for its anti-censorship purpose rather than for general transaction prioritization, which should remain a function of the fee market.

Ultimately, force inclusion is a foundational primitive for credible neutrality. It ensures that no single entity can control access to the blockchain's state transition function, which is vital for applications like on-chain voting, governance proposals, and arbitration systems where guaranteed execution is paramount. As blockchain scaling evolves with rollups and alternative data availability layers, variations of force inclusion are being standardized to protect users across the entire modular stack.