> This page is for SDK, version Legacy.
> For other versions, use one of these documentation indexes:
> - Current (default): https://buildwithfern.com/learn/sdks/current/llms.txt
> - Legacy: https://buildwithfern.com/learn/sdks/legacy/llms.txt

> For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://buildwithfern.com/learn/llms.txt.

## 2.63.0

**`(feat):`** 支持 `x-fern-default` 作为生成的 C# SDK 中参数的回退值。当请求头、查询参数或路径参数在 IR 中具有 `clientDefault` 值时，生成的 C# SDK 将该参数设为可选，并自动应用默认值。