Author: imToken

If you often shuttle across chains between Base, Arbitrum, or Optimism, you must have felt a subtle sense of "disconnection."

Although a single L2 transaction almost yields results in seconds, when you try to transfer assets from chain A to chain B, you often have to endure several minutes or even longer waiting times. This is not because L2 itself is not fast enough, but because in the traditional process, a transaction involving cross-layer and cross-chain must go through a lengthy and rigorous path:

L2 sequencer sorting → Submission to L1 → L1 reaching consensus and finality. In summary, under the current Ethereum architecture, L1 finality usually takes two epochs (about 13 minutes). This is undoubtedly necessary for security, but it seems overly slow for interoperability (Interop).

After all, if according to Ethereum's grand vision, there will be hundreds or thousands of L2s in the future, they should not be isolated execution islands but should work together as a whole. The key issue is whether we can shorten this waiting time as much as possible.

It is against this backdrop that the Ethereum Interop roadmap, in the acceleration phase, clearly proposes three highly coordinated improvement directions: Fast L1 Confirmation Rule, Shorter L1 Slots, and Shorter L2 Settlement.

It can be said that this is not a series of scattered optimizations, but a systematic reconstruction centered around "confirmation, rhythm, and settlement."

1. Fast Confirmation Rule: Provide the system with a "trustworthy answer" before Finality

As we all know, under the current Ethereum architecture, the mainnet block interval is about 12 seconds, and validating nodes vote on the current chain state at each slot, while finality lags behind multiple slots.

In short, even if a transaction has been packed into a block, the system still needs to wait a long time to be sure it will not be reorganized or rolled back. Currently, a transaction is considered final and irreversible only after about two epochs (approximately 13 minutes), which is undoubtedly too long for most on-chain financial scenarios.

So can we provide applications and cross-chain systems with a "fast and trustworthy" confirmation signal before Finality arrives? This is also what Project #4: Fast L1 Confirmation Rule aims to achieve in the Ethereum Interop roadmap.

Its core goal is very straightforward: to allow applications and cross-chain systems to receive a "strong and verifiable" L1 confirmation signal within 15–30 seconds, without having to wait for the full 13 minutes required for finality.

Mechanically, the fast confirmation rule does not introduce a new consensus process but reuses the attester voting that occurs at each slot in the Ethereum PoS system. When a block has accumulated enough and sufficiently distributed validator votes in early slots, it can be considered "extremely unlikely to be rolled back under a reasonable attack model," even if it has not yet entered the finality stage.

In simple terms, this level of confirmation does not replace finality but provides a strong confirmation recognized by the protocol before finality. This is particularly crucial for Interop: cross-chain systems, intent solvers, and wallets no longer need to wait blindly for finality but can safely advance the next logical step based on protocol-level confirmation signals within 15–30 seconds.

Currently, the preconfirmation narrative strongly promoted by Based Rollup serves as an important engineering transitional role in this direction. Its logic is quite simple; as the name suggests, imagine this:

When we purchase train tickets on 12306, once we select the itinerary and place the order (sign the transaction), the ticketing system first provides a preconfirmation message, informing you that the ticket purchase action (corresponding to each transaction) has been accepted and is entering the subsequent confirmation process. At this point, we can start planning our trip and preparing our luggage, and only when the ticket is finally confirmed with the carriage and seat (the transaction is published to L1) do we consider the ticket purchase transaction officially completed.

In short, in Based Rollup, preconfirmation means that before the transaction is officially submitted to L1 for confirmation, it commits to including the transaction in a block, effectively giving users an initial confirmation signal, letting them know that the transaction has been accepted and is being processed.

"I'll give you a strong verbal commitment first, and finalize later," through this layered confirmation logic, the Ethereum Interop roadmap effectively delineates different trust levels between "security" and "speed," creating a smoother interoperability experience.

2. Shorter L1 Slot: Accelerate Ethereum's "heartbeat" cycle

Complementing the fast confirmation rule's "logical reconstruction at the consensus level" is a more fundamental and physically meaningful change—shortening the size of slots.

If fast confirmation is like "writing an IOU" before consensus is reached, then shortening L1 slot time is directly reducing the "settlement cycle" of the ledger. In the Interop roadmap, Project #5's phased goal is very clear: to compress the Ethereum mainnet's slot time from the current 12 seconds to 6 seconds.

This seemingly simple "halving" will trigger a chain reaction throughout the entire chain. This is easy to understand; shorter slots mean that the rhythm of transactions being included in blocks, distributed for validation, and confirmed through observation is faster, resulting in lower overall protocol layer latency.

The impact on user experience is also very direct, including faster perceived confirmation for L1 interactions (such as ETH transfers), tighter rhythms for L2 state submissions to L1, and even the combination of shorter slots and fast confirmation rules essentially forming "near real-time on-chain feedback," which means that DApps, wallets, and cross-chain protocols in the ecosystem can better build a "second-level confirmation experience."

For cross-chain interoperability protocols, the reduction in time also means a leap in capital utilization. Currently, cross-chain bridges or market makers must bear the "capital in transit" risk for several minutes or longer when handling asset scheduling between different chains. To hedge against the volatility risk during this time, they have to charge higher fees.

When the L1 settlement cycle is shortened and the capital turnover speed doubles, the occupation of capital in transit will significantly decrease. The result is evident: lower friction costs, lower user fees, and shorter arrival delays, which will greatly incentivize developers and users to return to the secure L1 settlement layer rather than relying on fragile third-party relays.

Of course, increasing the "heartbeat" frequency is no easy task. Multiple working groups within the Ethereum Foundation are simultaneously advancing this complex engineering task:

• Network Analysis: Research teams (including researchers like Maria Silva) are conducting rigorous data analysis to ensure that shorter slots do not lead to severe reorganization risks due to network delays or impose centralization pressure on home nodes with poor bandwidth;
• Client Implementation: This involves a comprehensive underlying reconstruction of both the consensus layer and the execution layer. It is worth noting that this work is independent of EIP-7732 (native staker-builder separation ePBS), meaning that regardless of the progress of ePBS, the heartbeat acceleration plan can advance independently;

Overall, when the 6-second slots are combined with the fast confirmation rule, Ethereum is expected to truly achieve "near real-time on-chain feedback," allowing DApps and wallets in the ecosystem to create an unprecedented second-level confirmation experience.

3. Shorter L2 Settlement: Allow assets to be "withdrawn immediately"

In the Interop roadmap, Project #6: Shorter L2 Settlement is the most controversial but also the most imaginative part.

Under the current architecture, Optimistic Rollups typically rely on a challenge period of up to 7 days, and even ZK Rollups are limited by the rhythm of proof generation and verification. To be fair, this design is impeccable in terms of security, but it brings a practical problem at the interoperability level:

Assets and states are "time-locked" between chains. This not only raises cross-chain costs but also significantly increases the rebalancing burden on solvers, ultimately reflecting in higher user fees. Therefore, shortening the settlement cycle is seen as one of the key levers for whether Interop can scale. Current main engineering directions include:

• ZK Real-time Proofs: With hardware acceleration and recursive proofs maturing, proof generation time is being compressed from minutes to seconds;
• Faster Settlement Mechanisms: For example, introducing a secure 2-out-of-3 settlement model;
• Shared Settlement Layer: Allowing multiple L2s to complete state changes under a unified settlement semantics, rather than "withdraw—wait—deposit";

Of course, in the discussion of Interop, a core question that cannot be avoided is whether compressing the settlement challenge period from the traditional 7 days to 1 hour to achieve faster cross-chain confirmation will leave room for attackers to act maliciously.

Theoretically, this concern is not unfounded. Unlike "strong censorship" (where validating nodes collectively act maliciously), what is more concerning in reality is the soft censorship attack led by block builders: attackers do not need to control consensus; they only need to continuously suppress defenders in bidding, preventing key transactions from being included on-chain.

Interestingly, the only systematic economic analysis of such scenarios currently comes from Offchain Labs' paper "Economic Censorship Games in Fraud Proofs," published in February 2025. This paper constructs three models, from the most pessimistic to relatively optimistic, assuming:

• G¹ Model: Block content is entirely determined by the highest bidder;
• G¹ₖ Model: Some validators always locally build blocks;
• Gᵐ Model: Multiple validators jointly decide block content, as long as one party chooses the defender's transaction.

In practical engineering, since validators may choose empty slots (miss slots), some designs may even degrade to the more pessimistic G¹ scenario, so the paper chooses to analyze from the worst-case scenario.

Based on this premise, the researchers propose a highly practical defensive idea—a "small bet for a big win" delay defense mechanism, where the core logic is that defenders have the right to "one-click delay," meaning defenders do not need to complete all complex error-checking processes in a short time but only need to successfully submit a key transaction.

The role of this key transaction is very clear; once on-chain, it will automatically extend the challenge period from 1 hour back to the traditional 7 days. For example, when a defender detects an anomaly in the L2 state, they do not need to complete all the complex error-checking processes within 1 hour; they only need to successfully submit a special transaction to L1. This transaction acts like sounding an air raid alarm, instantly extending the challenge period back to the traditional 7 days.

This also means that attackers will be forced into a highly asymmetric war of attrition. To prevent this transaction from being included on-chain, attackers must continuously pay a higher priority fee than the defender in every block, and this confrontation must be maintained throughout the entire challenge period.

The quantitative results provided in the paper are also very intuitive. According to calculations, if a powerful attacker is prepared to spend $10 billion on a sustained censorship attack, then:

• In a 1-hour window, the defender only needs to prepare a gas budget of $33 million to counterattack;
• If the delay mechanism is successfully triggered, extending the challenge period to 7 days, the defender's counterattack cost could even drop to around $200,000;

In other words, this is an extremely critical structural advantage: the attacker's costs are linearly additive, while the defender only needs to successfully get one transaction on-chain.

It is this disparity in the cost-to-attack versus cost-to-defend ratio that ensures that even if the settlement cycle is significantly compressed, Ethereum still possesses strong robustness in economic security.

For Interop, this is also crucial, as it means that fast confirmation and shorter settlement cycles do not necessarily come at the expense of security, and it also indicates that under reasonable institutional design, second-level cross-chain and economic security can coexist. At the very least, it provides the most solid underlying confidence for achieving second-level cross-chain interoperability.

In Conclusion

Some may wonder why we should go to such lengths to optimize these few seconds or minutes of delay.

In the geek era of Web3, we have become accustomed to waiting, even believing that "waiting" is a premium that must be paid for decentralization. But on the road to Web3 becoming mainstream, users should not, and do not need to, care about which chain they are operating on, nor should they have to calculate the finality logic of L1.

Fast confirmation, 6-second heartbeats, and asymmetric defense mechanisms are essentially doing one thing—erasing the variable of "time" from the user's perception.

As I often say, the best form of technology is one that makes complexity completely disappear in rapid confirmation.

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