Ethereum's "second-level" evolution: from fast confirmation to settlement compression, how does Interop eliminate waiting time?

Author: imToken

If you often cross-chain between Base, Arbitrum, or Optimism, you must have felt a subtle sense of “fragmentation.”

Although individual L2 transactions are almost instant, when you try to transfer assets from chain A to chain B, you often have to wait several minutes or even longer. This is not because L2 itself is slow, but because in traditional processes, a cross-layer, cross-chain transaction must go through a lengthy and rigorous process:

L2 sequencer ordering → Submission to L1 → L1 reaching consensus and finality, in short, under the current Ethereum architecture, finality on L1 usually takes about two Epochs (roughly 13 minutes). While this is necessary for security, it is too slow for interoperability (Interoperability).

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

Against this backdrop, Ethereum’s Interop roadmap, during the acceleration phase, clearly proposes three highly coordinated improvement directions: Fast L1 Confirmation Rule, Shorter L1 Slots, and Shorter L2 Settlement Cycles.

This is not just scattered optimization but a systemic overhaul around “confirmation, pacing, and settlement.”

1. Fast Confirmation Rule: Providing a “Trustworthy Answer” Before Finality

As is well known, in the current Ethereum architecture, the mainnet block time is about 12 seconds. Validator nodes vote on the current chain state in each slot, and finality is achieved after several slots.

In short, even after a transaction is included in a block, the system still needs to wait a long time to be confident it won’t be reorganized or rolled back. Currently, it takes about two Epochs (roughly 13 minutes) for a transaction to be considered final. For most on-chain financial scenarios, 13 minutes is undoubtedly too long.

Can we provide applications and cross-chain systems with a “fast and sufficiently trustworthy” confirmation signal before finality arrives? This is exactly what Project #4: Fast L1 Confirmation Rule in Ethereum’s Interop roadmap aims to do.

Its core goal is straightforward: enable applications and cross-chain systems to receive a “strong and verifiable” L1 confirmation signal within 15–30 seconds, without waiting for the full 13-minute finality.

Mechanistically, the fast confirmation rule does not introduce a new consensus process but reuses the attester votes that occur in each slot within Ethereum’s PoS system. When a block in early slots has accumulated enough, sufficiently dispersed validator votes, it can be considered “extremely unlikely to be rolled back under reasonable attack models,” even if it has not yet reached finality.

In simple terms, this confirmation level does not replace finality but provides a protocol-acknowledged strong confirmation before finality. For Interop, this is especially critical: Cross-chain systems, Intent Solvers, and wallets no longer need to blindly wait for finality but can confidently proceed within 15–30 seconds based on protocol-level confirmation signals.

Currently, preconfirmation (Preconfirmation), heavily promoted by the Based Rollup narrative, plays an important transitional role in this direction. Its logic is simple: imagine:

When buying train tickets on 12306, once you select your trip and sign the transaction, the booking system first provides a pre-confirmation message, telling you that your purchase (each transaction) has been accepted and is entering the subsequent confirmation process. At this point, you can start planning your trip, packing, etc. Only when the ticket is finally confirmed with a seat (transaction published to L1) do you officially complete the booking.

In short, in Based Rollup, preconfirmation means promising to include the transaction in a block before it is officially submitted to L1 for confirmation. It’s like giving users an initial confirmation signal, letting them know the transaction has been accepted and is being processed.

“This is a strong verbal commitment first, with final confirmation to follow later.” Through this layered confirmation logic, Ethereum’s Interop roadmap effectively delineates different trust levels between “security” and “speed,” creating a smooth interoperability experience.

2. Shortening L1 Slot: Accelerating Ethereum’s “Heartbeat” Cycle

Complementing the fast confirmation rule—a “consensus-layer” logical overhaul—is a more fundamental, physically meaningful change: shortening the size of each Slot.

If fast confirmation is like “IOU” before final consensus, then shortening L1 Slot time directly shortens the ledger’s “settlement cycle.” In the Interop roadmap, Project #5’s phased goal is clear: reduce Ethereum mainnet’s Slot time from the current 12 seconds to 6 seconds.

This seemingly simple “halving” will trigger chain-wide ripple effects. It’s easy to understand: shorter slots mean transactions are included in blocks, distributed, validated, and confirmed more quickly, resulting in lower overall protocol latency.

The impact on user experience is direct: faster perceived confirmation for L1 interactions (like ETH transfers), more tightly paced state submissions from L2 to L1, and when combined with the fast confirmation rule, it forms an “almost real-time on-chain feedback,” enabling DApps, wallets, and cross-chain protocols to build “second-level confirmation experiences.”

For cross-chain interoperability protocols, shorter timeframes mean a leap in capital utilization. Currently, bridges or market makers handling assets across chains face “in-transit” risk that can last minutes or longer. To hedge against this volatility, they charge higher fees.

When L1 settlement cycles are shortened and capital turnover speeds up, the capital in transit is significantly reduced. The result is clear: lower friction costs, lower user fees, and shorter arrival delays, greatly encouraging developers and users to return to the secure L1 settlement layer rather than relying on fragile third-party relays.

Of course, doubling the “heartbeat” frequency is no trivial task. Multiple working groups within the Ethereum Foundation are advancing this complex engineering effort:

• Network Analysis: Researchers (including Maria Silva and others) are conducting rigorous data analysis to ensure that shorter Slots do not cause severe chain reorganizations (reorgs) due to network delays or centralization pressures on less capable nodes;
• Client Implementation: This involves comprehensive low-level restructuring of both consensus and execution layers. Notably, this work is independent of EIP-7732 (native stakers - builder separation ePBS), meaning that regardless of ePBS progress, the heartbeat acceleration plan can proceed independently;

Overall, when 6-second Slots are combined with the fast confirmation rule, Ethereum is poised to achieve “near real-time on-chain feedback,” enabling the ecosystem’s DApps and wallets to deliver unprecedented second-level confirmation experiences.

3. Shortening L2 Settlement Cycle: Making Assets “Instant Withdraw and Transfer”

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

Under current architecture, optimistic rollups typically rely on a 7-day challenge period, and even ZK rollups are limited by proof generation and verification speeds. Truthfully, this design is impeccable in security but introduces a practical problem at the interoperability layer:

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 reflected in higher user fees. Therefore, shortening the settlement cycle is seen as a key lever for scalable Interop. The main engineering directions include:

• Real-time ZK proofs: With hardware acceleration and recursive proofs maturing, proof generation time is shrinking from minutes to seconds;
• Faster settlement mechanisms: such as introducing secure 2-out-of-3 settlement models;
• Shared settlement layers: enabling multiple L2s to change states under a unified settlement semantic, rather than “withdraw—wait—deposit.”

Of course, a core question in Interop discussions is whether compressing the challenge period from the traditional 7 days to 1 hour to achieve faster cross-chain confirmation might leave room for malicious attacks.

Theoretically, this concern is not unfounded. Unlike “strong censorship” (validator collusion), a more realistic threat is a soft censorship attack led by block proposers: attackers do not need to control consensus but can continuously suppress defenders’ bids, preventing key transactions from being included on-chain.

Interestingly, the only systematic economic analysis of such scenarios comes from Offchain Labs’ February 2025 paper “Economic Censorship Games in Fraud Proofs,” which models three scenarios from most pessimistic to relatively optimistic:

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

In practice, since validators might choose empty slots (miss slots), some designs even degenerate into the worst-case G¹ scenario. The paper analyzes from this worst case.

Based on this, the researchers propose a highly practical defense strategy—“small bet, big defense” delay mechanism. Its core logic is that defenders have the “one-click delay” right: they do not need to complete all complex fault detection within a short window but only need to successfully submit a key transaction.

This key transaction’s role is clear: once on-chain, it automatically extends the challenge period from 1 hour back to the traditional 7 days. For example, if a defender detects abnormal L2 state, they do not need to complete all fault detection within 1 hour. They only need to successfully submit a special transaction to L1, which acts like an alarm, instantly extending the challenge period back to 7 days.

This forces attackers into a highly asymmetric cost game: to prevent this transaction from being included, attackers must continuously pay higher priority fees in each block, maintaining this adversarial stance throughout the challenge period.

The paper’s quantitative analysis shows that if a well-funded attacker is willing to spend $10 billion on sustained censorship attacks, then:

• During the 1-hour window, defenders only need about $33 million in gas budget to counterattack;
• If the delay mechanism is successfully triggered, extending the challenge period to 7 days, the defender’s counterattack cost drops to around $200,000;

In other words, this is a critical structural advantage: the attacker’s cost scales linearly, while the defender only needs to succeed once to include their transaction.

This enormous attack-defense cost ratio (Cost to Attack vs. Cost to Defend) ensures that even with significantly compressed settlement cycles, Ethereum maintains strong economic security.

For Interop, this is also crucial: it shows that fast confirmation and shorter settlement cycles do not necessarily come at the expense of security. With proper system design, second-level cross-chain and economic security can coexist—at least providing a solid foundational confidence for achieving second-level cross-chain experiences.

Final Words

Some might wonder: why bother optimizing these few seconds or minutes of delay?

In the Web3 geek era, we are used to waiting, and even believe that “waiting” is a premium paid for decentralization. But as Web3 moves toward mass adoption, users should not, and need not, care about which chain they are operating on, nor should they need to think about L1 finality logic.

Fast confirmation, 6-second heartbeat, and asymmetric defense mechanisms fundamentally serve one purpose—removing the variable of “time” from the user’s perception.

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