# Update Preview

## books50 Depth Channel: Incremental Push

**Live date:** November 5, 2026

Interface:
- WebSocket `books50` depth channel (JSON)
- WebSocket SBE Depth50 channel (`books50`, templateId=1001)

Changes:
- The `books50` channel will change from full snapshot on every push to incremental push: the first push after subscription is a full `snapshot`, and all subsequent pushes are incremental `update`s. This applies to both the JSON text-frame channel and the SBE binary channel.
- The `pseq` push parameter will also have a value for the `books50` channel (previously only for the `books` channel), and can be used to determine whether there has been packet loss.
- On the SBE side, the schema version will be raised to `5`, and the `Depth50` message (templateId=1001) will carry two additional fields: `depthAction` (`0` = `snapshot`, `1` = `update`) to distinguish the two frame types explicitly, and `pseq` for packet-loss detection.
- Currently effective in **demo trading**.