Today, we continue our exploration of the Rollup narrative. As described in previous articles, this is a vast family, with each member carrying unique technical DNA and application visions, all playing indispensable roles on the blockchain stage.

And today, the member we are diving into — Based Rollup — is arguably the most sensitive one in this family.

Back to the core topic. In the world of Rollups, we have become accustomed to one key role: the Sequencer. It is responsible for ordering transactions, batching blocks, and submitting state to L1. It is the “heart” of most Rollups. But precisely because of this, the Sequencer has also become the most sensitive component in the system:

• Who controls transaction ordering?

• Can transactions be censored?

• Can MEV be extracted?

• What happens if the Sequencer goes down?

The emergence of Based Rollup is essentially an answer to one fundamental question:

Can we get rid of the Sequencer altogether?

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A One-Sentence Definition of Based Rollup

Based Rollup = a Rollup that hands transaction ordering directly to L1.

In traditional Rollups, the flow looks like this:Users → send transactions to the Sequencer → the Sequencer performs local ordering and execution → results are submitted to L1.

In a Based Rollup, the process changes to:User transactions enter the L1 mempool directly → L1 validators/miners determine the ordering → the Rollup only handles execution and state proofs.

In other words, the Rollup no longer decides ordering itself, but instead reuses L1’s consensus ordering. This is the meaning of “Based” — based on L1’s ordering and liveness.

Why Design It This Way?

The problems introduced by Sequencers boil down to two dimensions: liveness risk and concentration of power.
Even if a Rollup inherits L1 security at the settlement layer, it still heavily depends on a centralized actor at the “process layer.”

The logic of Based Rollup is straightforward:If we ultimately have to trust L1 anyway, why not let L1 control ordering from the very beginning?

This naturally brings several properties:

• No centralized Sequencer required

• Stronger censorship resistance

• MEV aligned with L1

• Liveness directly inherited from L1

At its core, this turns a Rollup from a “semi-independent system” into an execution extension of L1 itself.

The Core Structure of Based Rollup

A Based Rollup can be broken down into three components:

1. Ordering Layer: Entirely on L1

Transactions enter the Ethereum (or other L1) mempool directly.Block ordering is determined by L1 blocks, with no additional ordering protocol required, and censorship resistance is shared with L1.This is the biggest point of divergence.

2. Execution Layer: Still on the Rollup

Although ordering happens on L1, actual execution is still performed by the Rollup client:

• Compute state transitions

• Generate state roots

• Produce ZK or Optimistic proofs

3. Settlement Layer: Same as Standard Rollups

Final results are still submitted to L1 and protected by Fraud Proofs or Validity Proofs.
Assets remain custody-managed by L1 contracts.

Therefore:Based Rollup ≠ a new security model

It is a new ordering model.

The Causal Relationship Between the Layers

One easily overlooked detail is that these layers are not equal peers — they have a strict causal relationship.

• The ordering layer defines the “timeline of the world”

• The execution layer computes state transitions along that timeline

• The settlement layer anchors the result as final truth

This is the exact inverse of traditional Rollups:

• Previously: Rollup decides ordering → submits a “fait accompli” to L1

• With Based Rollup: L1 decides ordering first → Rollup can only compute within that order

This inversion may look simple, but it produces a crucial shift:The Rollup transforms from a semi-autonomous system into an execution plugin within L1’s consensus process.

Real Constraints Between the Layers

1. The Ordering Layer Strongly Constrains Execution

Once transaction ordering is fixed by L1 blocks, the Rollup client has zero flexibility:

• No reordering

• No filtering

• No queue-jumping

It behaves like a deterministic virtual machine that produces a single output for a fixed input.

This makes Rollup execution resemble an “offline EVM calculator” for Ethereum.

2. Execution Produces Verifiable Output for Settlement

Whether ZK or Optimistic, both answer the same question:Given L1-defined ordering, did the state transition follow the rules?

The proof does not concern who ordered transactions, but whether computation was correct under that order.

3. A Fundamental Contrast with Traditional Rollups

• Traditional trust path: User → Sequencer → Rollup → L1

• Based Rollup trust path: User → L1 → Rollup → L1

The “powerful intermediary” in the middle is removed.

That is why we say: Based Rollup does not introduce a new security model — it realigns the power structure.

Security still comes from:

• L1 data availability

• Correctness of the proof system

• Immutability of settlement contracts

Only one thing truly changes: who determines historical ordering.And in blockchains, ordering power is often the highest form of power.

A More Engineering-Oriented Mental Model

You can think of Based Rollup as:

• L1: the operating system kernel

• Rollup: a user-space execution process

The process can perform complex computation, but scheduling authority always belongs to the kernel.This is the fundamental difference from standard Rollups.

What Problems Does Based Rollup Actually Solve?

1. Censorship Resistance

In traditional architectures, a Sequencer can:

• Refuse transactions

• Delay inclusion

• Selectively reorder

Users must wait or force transactions onto L1.

In a Based Rollup, as long as a transaction can be included on L1, the Rollup must accept it.
Censorship difficulty and attack cost therefore become equivalent to attacking L1 itself.

2. MEV Redistribution

This is the most “political” aspect of Based Rollups.

• Traditional model: MEV accrues to the Sequencer, separated from L1 and capable of forming a new power center

• Based Rollup: MEV flows directly into L1’s value stream, aligning with PBS (Proposer-Builder Separation) and the broader L1 economic system

In effect, instead of creating a small kingdom at L2, MEV returns to L1’s open marketplace.

3. Liveness Inheritance

• Worst case for normal Rollups: Sequencer goes offline → users must force exit → degraded experience

• Based Rollup: as long as L1 continues producing blocks, the Rollup remains usable, with no special emergency mechanism required

This is an especially elegant engineering property.

There Is No Free Lunch: The Trade-offs

1. Higher Costs

Every transaction must first land on L1. Costs approach calldata-level gas usage, and efficiency is lower than centralized Sequencer batching.

2. Higher Latency

Ordering follows L1 block times. Sub-second confirmations are impossible, and user experience resembles L1 more closely — unfriendly for high-frequency use cases.

3. Reduced Design Flexibility

Many Sequencer-driven optimizations are hard to implement:

• Pre-confirmations

• Private mempools

• Custom ordering logic

These are largely incompatible with the Based model.

Therefore, Based Rollups Are Better Suited For:

• Security-first rather than UX-first systems

• Decentralization over speed

• Use cases strongly aligned with L1

A More Intuitive Analogy

• Traditional Rollup: runs its own company, only filing accounts with the central bank

• Based Rollup: directly uses the central bank’s clearing system and focuses solely on business execution

Their power structures are fundamentally different.

Conclusion

Based Rollup is not a “faster Rollup,” but a “more L1-like Rollup.”

It sacrifices some performance and flexibility in exchange for:

• Pure censorship resistance

• The simplest possible trust model

• Full alignment with L1’s economic structure

Whether this path will become mainstream remains uncertain.
But it clearly highlights one thing:

The endgame of Rollups may not be to look more like L2 — but to become an integral part of L1 itself.