feat: add reasoning_content field to CreateResponseMessage

[Kemel91]

What:

• Bug Fix
• New Feature

Description:

Add support for the reasoning_content field in chat completions API responses. This field is added at the same level as content in both streaming and non-streaming requests. The field is marked as optional to handle cases where it's not present in the API response.

Related:

fixes #517

[iBotPeaches]

Am I blind? I can't find that property on the API reference: https://platform.openai.com/docs/api-reference/chat/object

[Kemel91]

Am I blind? I can't find that property on the API reference: https://platform.openai.com/docs/api-reference/chat/object

The reasoning_content field is indeed not yet listed in the official OpenAI API reference.

However, this field is currently being returned by the API when using certain experimental or yet-to-be-documented features (e.g., when the reasoning option is enabled in the request).

We added support for it in the library to:

Avoid data loss: If the API does return this field, the library will now parse it correctly.

Stay ahead of future updates: New fields often appear in the API before they are officially documented.

Support users already experimenting with the feature: Some developers are already using unreleased capabilities, and the library shouldn’t break or ignore the data.

This is a common practice in SDKs to maintain compatibility with potential API changes before they are formally announced.

[iBotPeaches]

Okay, update/create some tests and I think we are good to go.

[Cyrille37]

Thanks, guys! 💌