> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://okx-demo.ferndocs.com/docs/resources/changelog/2026/2/20/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://okx-demo.ferndocs.com/_mcp/server.

## Order book trading

* Added `POST /api/v5/trade/mass-cancel` to cancel all open orders for a given
  instrument family in a single request, primarily for options market makers.
* The `attachAlgoOrds` parameter on `POST /api/v5/trade/order` now supports
  attaching multiple take-profit / stop-loss brackets to a single order.
* Added the `linkedAlgoOrd` field to `GET /api/v5/trade/order` responses,
  surfacing the algo order id linked to a placed order.