> For the complete documentation index, see [llms.txt](https://corpus-core.gitbook.io/specification-colibri-stateless/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://corpus-core.gitbook.io/specification-colibri-stateless/specifications/op-stack.md).

# OP-Stack

## OpPreconf

Preconfirmation structure containing a sequencer-signed execution payload. Preconfirmations are OP-Stack sequencer commitments that provide early block availability.

The Type is defined in [src/chains/op/ssz/op\_proof\_types.h](https://github.com/corpus-core/colibri-stateless/blob/dev/src/chains/op/ssz/op_proof_types.h#L48).

```python
class OpPreconf(Container):
    payload   : Union [         # the execution payload (compressed or uncompressed)
        Bytes[1073741824],      # ZSTD-compressed execution payload (domain + payload)
        Bytes[1073741824]]      # uncompressed execution payload (domain + payload)
    signature : ByteVector [65] # the sequencer signature (65 bytes: r, s, v)
```