Chain Quality (CQ) is a core property of blockchains. Informally, it means: if you hold 3% of the staked stake, then over an average time period, you control 3% of the block space. For early blockchains with low throughput, chain quality is already sufficiently applicable.

However, modern blockchains have significantly higher bandwidth—so much so that a single block can contain a large number of transactions. This gives rise to a stronger and more granular concept. It goes beyond merely ensuring the average proportion of block space allocated over time, and instead focuses on how block space is partitioned within each individual block. We call this “Strong Chain Quality” (SCQ): if you hold 3% of the staked stake, then in every block, you control 3% of the block space. Fundamentally, this property grants stakeholders “virtual lanes” inside a high-throughput blockchain, thereby guaranteeing inclusion of their transactions.

One of Bitcoin’s key innovations—now present in nearly every blockchain—is the introduction, within the protocol itself, of a reward mechanism for block proposers: the party that successfully appends a block to the state machine receives newly minted tokens and transaction fees. These rewards are specified by the state transition function and ultimately reflected in the system state. In traditional distributed computing models, participants are divided into honest and malicious parties. There is no need to reward honest behavior, because honesty is assumed by default in the model. In contrast, in cryptoeconomic models, participants are viewed as rational agents whose utility functions may be unknown. The goal is to design incentives such that, in pursuing their own profit maximization, these participants naturally align with the successful operation of the protocol.

Combining this in-protocol reward mechanism, we arrive at the following idealized definition of chain quality:
Chain Quality (CQ): A coalition holding X% of the total staked stake has an X% probability of being the proposer of each block entering the chain after Global Stabilization Time (GST). If a chain deviates from CQ requirements, certain coalitions may receive a disproportionately larger share of rewards—undermining the incentive for honest behavior and threatening protocol security. Many blockchains satisfy—or strive to satisfy—this property via “stake-weighted random leader rotation.” Typical current challenges include: Bitcoin’s “selfish mining” problem; Monad’s tail-fork resistance issue; and issues within Ethereum’s LMD GHOST protocol.

When block space is sufficiently abundant, there is no need to entrust the entire contents of a block to a single proposer. Instead, block space within the same block can be jointly partitioned among multiple participants. Strong Chain Quality (SCQ), as a cryptoeconomic definition, precisely captures this idea:
Strong Chain Quality (SCQ): A coalition holding X% of the total staked stake can control X% of the block space in every block after Global Stabilization Time (GST). This idealized property implicitly introduces the abstraction of “virtual lanes”—i.e., the coalition effectively controls a dedicated, proportional portion of block space in every block.

From an economic perspective, owning a virtual lane is equivalent to holding a productive, revenue-generating asset—revenues potentially derived from transaction fees or MEV (Maximal Extractable Value). External entities compete for staked stake to acquire and maintain these lanes, thereby generating sustained demand for the underlying L1 token. The greater the economic value a lane can produce, the stronger the incentive for participants to stake—and the higher the value accumulated by the L1 staked stake that controls access to this block space. Through this abstraction, stronger censorship resistance can be translated into the protocol-level effectiveness of SCQ.

Recent research shows that censorship-resistant protocols are critically important. Such protocols must not only guarantee eventual inclusion of honest inputs but also ensure immediate inclusion. Strong Chain Quality (SCQ) can be viewed as an extension of this property under finite block capacity. In practice, if the volume of pending transactions exceeds available block space, no protocol can satisfy ideal censorship resistance. SCQ adopts a more pragmatic approach to this constraint: rather than demanding that all honest transactions always be included, it allocates a “budget” to each staking node—guaranteeing inclusion of its transactions within that budget.

The MCP protocol was proposed as a component layered atop existing practical Byzantine Fault Tolerance (PBFT)-style consensus protocols, specifically to endow them with censorship resistance. MCP simultaneously satisfies SCQ—allocating block space to proposers proportionally to their staked stake. Existing DAG-based BFT protocols provide a way to implement a multi-writer mempool and also offer some degree of censorship resistance. However, their standard implementations typically fail to strictly satisfy SCQ, since they allow leaders to selectively delay subsets of transactions. With minor modifications, though, these protocols could potentially re-achieve SCQ. A related direction is “forced transaction inclusion,” designed to reduce censorship. MCP further demonstrates how to realize a stronger hidden property: using it, stakeholders can create virtual private lanes whose contents remain concealed until the full block is publicly revealed.

To achieve Strong Chain Quality after Global Stabilization Time (GST), the key is ensuring proposers cannot arbitrarily censor stakeholders’ inputs. This can be achieved via a two-round protocol. Starting from virtually any view-based BFT protocol, only two small modifications are needed:
Round 1: Each participant broadcasts its authenticated input to all other participants.
Round 2: Each participant, upon receiving an authenticated input from participant i, adds i to its own inclusion list. It then broadcasts this inclusion list to the leader. This step amounts to a commitment: the participant will accept only blocks that include all inputs listed in its inclusion list.

BFT Proposal: Upon receiving these messages, the leader includes the union of all received inclusion lists in the block.
BFT Vote: A participant votes “yes” only if the block contains all inputs in its own inclusion list.
It is straightforward to see that, following this protocol sketch, a complete protocol can be constructed—one that satisfies Strong Chain Quality after GST, provides censorship resistance, and maintains liveness when the leader is honest. To achieve SCQ before GST, additional waiting per round for a sufficient number (quorum) of values or lists is required.

Recent research indicates that achieving both Strong Chain Quality and censorship resistance requires adding two extra rounds (as outlined in the above protocol sketch) atop the standard voting rounds of conventional BFT protocols. While Strong Chain Quality (SCQ) specifies the proportion of block space a coalition can control, it does not fully constrain the ordering of transactions within that space. SCQ can thus be understood as reserving space for each staking node—but making no guarantees whatsoever about the order of transactions within that reserved space. This opens up rich research avenues for designing transaction ordering mechanisms. A well-designed ordering mechanism holds promise to further enhance fairness and efficiency across the blockchain ecosystem.

[Foresight News]