> For the complete documentation index, see [llms.txt](https://docs.lumia.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lumia.org/ecosystem/lumia/chain-security/sequencer.md).

# Sequencer

**Who this is for:** developers who want to understand what determines transaction order and finality timing on Lumia before they build something order-sensitive (an AMM, an auction, a liquidation flow).

### What the sequencer does

The sequencer is the component that receives submitted transactions, orders them, and groups them into batches. On a validity-proof L2 like Lumia, the sequencer's output is what everything downstream operates on: [zkProvers](https://app.gitbook.com/s/chmhPiVNAafGw48c4oU2/ecosystem/lumia/chain-security/zkprovers) prove the batches it produces, and the resulting proofs are what eventually get settled back to Ethereum L1.

At any given time, transaction ordering on Lumia comes from a single sequencer. A single sequencer means fast, predictable ordering under normal operation, but it also means ordering liveness depends on that one component staying up; this design is common to CDK-based L2s generally, not unique to Lumia.

### Batching

Transactions are grouped into batches rather than proven one at a time: batching is what makes proof generation economical, since a proof's cost doesn't scale linearly with how many transactions it covers.

### Relation to zkProvers

The sequencer only orders and batches: it does not itself prove anything. Batch correctness is established by [zkProvers](https://app.gitbook.com/s/chmhPiVNAafGw48c4oU2/ecosystem/lumia/chain-security/zkprovers), which generate the proofs that let a batch be accepted as valid. A batch existing is not the same as a batch being proven; see the zkProvers page for what "proven" means on Lumia specifically.

The role split above, from a submitted transaction to L1 settlement:

```mermaid
flowchart LR
    U[User transaction] -->|submitted| S[Sequencer]
    S -->|orders and groups into a batch| B[Batch]
    B -->|proof generated| P[zkProvers]
    P -->|proof settled| L1[Ethereum L1]
```