Ethereum Protocol Shift: FOCIL and FairFIL Enforce Censorship Resistance

Woofun AI reports that Ethereum is fundamentally restructuring its transaction inclusion logic to eliminate centralized censorship risks, moving beyond reliance on a few powerful block builders toward protocol-enforced neutrality.

This shift addresses the core vulnerability where compliant transactions could be indefinitely delayed or excluded based on the subjective preferences of centralized participants, a scenario that undermines the network’s foundational promise of open access. The initiative, highlighted by imToken, underscores a critical technical evolution: ensuring that any transaction adhering to protocol rules—such as those initiated in an imToken wallet with sufficient balance and gas fees—is guaranteed a fair chance of being recorded in a block, rather than remaining in a perpetual "Pending" status while inferior transactions are processed. This transformation is not merely a political stance but a rigorous engineering response to the centralization inherent in current block-building practices, aiming to decouple transaction inclusion from the discretionary power of individual entities.

The origin of this censorship risk lies in the structural changes introduced by Ethereum’s transition to Proof of Stake and the subsequent adoption of the PBS (Proposer-Builder Separation) architecture. When a user signs and sends a transaction, it enters the mempool, a public waiting area for unconfirmed transactions.

However, entry into the mempool does not guarantee inclusion; someone must select, order, and package these transactions into a block. To mitigate the risk of large staking pools exploiting MEV (Maximal Extractable Value) to create economic monopolies, Ethereum separated the roles of Builder and Proposer. Builders are responsible for collecting transactions, optimizing their order for maximum profit through arbitrage and liquidation opportunities, and constructing candidate blocks.

Proposers, on the other hand, select one of these candidate blocks and submit it to the network for confirmation. This division was designed to allow ordinary validation nodes to participate in block proposals without needing the complex infrastructure required for MEV optimization, thereby preserving staking decentralization. Yet, this architectural choice inadvertently concentrated the power of transaction selection in the hands of a few specialized entities, creating a new vector for potential censorship.

The centralization risks associated with this block-building concentration are stark and quantifiable. Currently, over 90% of Ethereum blocks across the network are produced by just a handful of professional Builders. These entities typically operate with clear corporate backgrounds, making them susceptible to external pressures from regulatory bodies and legal frameworks in specific jurisdictions. For instance, Builders may face pressure to comply with the OFAC sanctions list, leading to the selective filtering of transactions involving sensitive contracts like Tornado Cash or addresses flagged by regulators. This creates a de facto "implicit ban" where certain transactions are excluded not due to protocol violations, but due to the risk-averse behavior of centralized participants. For ordinary users, Ethereum appears as an open network where anyone can transfer funds or interact with smart contracts.

However, from a protocol operation perspective, the ability of a transaction to take effect depends entirely on whether it is selected by these centralized Builders. If these entities act as gatekeepers, Ethereum’s operational reality diverges significantly from traditional financial systems, which are inherently permissioned and subject to similar regulatory constraints. The risk is that the network’s openness becomes conditional, dependent on the compliance posture of a few powerful actors rather than the immutable rules of the protocol.

To address this vulnerability, Ethereum researchers proposed the concept of Inclusion Lists, a mechanism designed to restore balance to the transaction inclusion process. The core logic is straightforward: while Builders retain the responsibility for constructing blocks and optimizing transaction order, they no longer hold unilateral power over which transactions are included. Validation nodes actively participating in Ethereum staking are granted the authority to submit a "must-board list" of transactions that must be processed. Using a bus station analogy, a block can be viewed as a bus with limited seating. Builders determine the seating arrangement to maximize efficiency and profitability, akin to deciding who sits where.

However, validation nodes can submit a list of passengers who must board the bus. As long as the transactions on this list are valid, willing to pay reasonable fees, and there is sufficient block space, Builders cannot ignore them based on personal or corporate preferences. This mechanism ensures that the power to exclude transactions is not concentrated in a single point of failure, introducing a layer of protocol-level oversight that constrains the discretionary power of Builders and enhances the network’s resistance to censorship.

Woofun AI data shows that FOCIL (Fork-Choice Enforced Inclusion Lists) represents a significant advancement in this domain by distributing the power to create inclusion lists across a decentralized committee. Instead of relying on a single proposer to decide which transactions must be included, FOCIL establishes a validation node committee composed of multiple randomly selected nodes during each block generation cycle. Each member of this committee independently observes the network mempool and submits their own local inclusion list.

This distributed approach ensures that even if 99% of Builders and proposers in the network attempt to censor a particular transaction, the presence of just one honest node in the committee that includes it in the list can trigger protocol-level constraints. The advantage of this design is that it does not require assuming neutrality from all committee members; it only requires a minimal threshold of honesty to override censorship attempts. If censors wish to exclude a transaction, they must bypass multiple independent participants rather than influencing a single entity, significantly raising the barrier to coordinated censorship and enhancing the robustness of the inclusion mechanism.

However, the existence of an inclusion list is insufficient without enforcement mechanisms. If a Builder ignores the list after receiving it, the inclusion list becomes a non-binding suggestion, rendering the entire system ineffective. To address this, FOCIL introduces the Fork-Choice Rule as a mandatory constraint, forcing all nodes responsible for voting and verification in the network to strictly examine the blocks submitted by Builders. If a Builder violates the inclusion list established by the committee, the entire network will refuse to vote for that block, effectively deeming it invalid.

This means that violating blocks are instantly rejected by the protocol, and the Builder faces significant penalties for failing to generate a valid block. The Fork-Choice Rule transforms the inclusion list from a soft recommendation into a hard protocol requirement, ensuring that censorship attempts are not only difficult to coordinate but also economically unviable. By aligning the incentives of validators with the enforcement of inclusion rules, FOCIL creates a self-sustaining mechanism that protects transaction integrity without relying on the goodwill of centralized participants.

FairFIL (Fair Forward Inclusion Lists) complements FOCIL by introducing an accountability mechanism that makes censorship economically costly and unsustainable. While FOCIL focuses on preventing censorship through consensus rules, FairFIL emphasizes the need for public records and verifiable explanations for why certain transactions were not included in a block. In actual network operations, Builders may require a short buffer period to optimize transaction ordering and pursue MEV arbitrage opportunities.

FairFIL allows for this flexibility under certain constraints, but if a Builder continues to censor transactions in subsequent blocks, the protocol initiates an accountability process. The logic involves three steps: first, the protocol establishes public, verifiable reference rules to determine which transactions in the mempool qualify for inclusion. If eligible transactions are omitted, Builders must publicly list them in FairFIL.

Second, validators check the completeness of this list, detecting any deliberate omissions. Third, valid transactions listed in FairFIL become priority tasks for subsequent blocks, and repeated omissions can lead to the loss of validator support and economic penalties, including the slashing of staking deposits. This progressive penalty structure ensures that censorship is not only visible but also financially ruinous for those who attempt it.

For ordinary users interacting with DeFi protocols or using wallets for daily transactions, these underlying mechanisms do not require changes to existing habits. Users will continue to enter amounts, confirm gas fees, and sign transactions in their wallets, waiting for confirmation.

However, the certainty of the transaction inclusion process is significantly enhanced. A compliant transaction no longer relies entirely on the discretion of a single Builder; even if the current Builder is unwilling to process it, other validators can enforce its inclusion through protocol-level requirements. The power to include transactions is gradually separating from the power to order them, allowing Builders to continue optimizing for MEV while restricting their ability to decide "who is eligible to enter the market.' This shift towards credible neutrality means that users do not need to trust the neutrality of specific Builders; instead, they can rely on protocol rules automatically enforced by clients. Validation nodes will check blocks against the same set of rules, making it difficult for blocks that violate inclusion obligations to gain network acceptance, thereby reinforcing the integrity of the Ethereum ecosystem.

The current development status of these mechanisms reflects a structured progression towards implementation. As of August 2026, EIP-7805, which corresponds to FOCIL, is in the Draft stage but has been selected as a Headliner for the Hegotá upgrade’s consensus layer. It has entered the Scheduled for Inclusion phase, meaning client teams have agreed to implement and test it on the network, although the exact mainnet launch date remains unfinalized. FairFIL is at an earlier stage, currently a research proposal released in July 2026.

Its inclusion in Ethereum’s roadmap requires broader discussion, implementation, and security verification. Looking ahead, wallets and block explorers may provide more detailed transaction statuses, indicating whether a transaction is on an inclusion list, has received inclusion obligations, or is delayed due to insufficient gas, nonce conflicts, or expired contract execution conditions. This transparency will empower users with better insights into the status of their transactions, distinguishing between protocol-level delays and network congestion issues.

In conclusion, Ethereum’s journey from value statement to protocol reality underscores a fundamental shift in how censorship resistance is achieved. It is impossible to guarantee that every Builder, validator, and infrastructure operator will always remain neutral, as participants may face regulatory pressure, pursue self-interest, or accept external incentives. A truly resilient decentralized network cannot rely on the ideal assumption that "everyone will do the right thing.'

Instead, it must ensure that even if some participants attempt to interfere, others have the ability to break such control. By making censorship visible, costly, and unsustainable through mechanisms like FOCIL and FairFIL, Ethereum is transforming its promise of neutrality from a philosophical ideal into a technical reality. This evolution ensures that the network remains open and accessible, protecting the rights of all users to have their transactions included in the blockchain, regardless of external pressures or centralized interests.