Environment

• Positron version: 2026.05.1 build 2
• OS: macOS
• Positron Assistant provider: Custom Provider
• API provider: Kimi / Moonshot AI
• Base URL used: https://api.moonshot.cn/v1
• Model override used: kimi-k2.6
• Same configuration worked before update: Yes
• Another OpenAI-compatible provider tested: DeepSeek API works fine in new version

Problem

After updating Positron to the latest version, I can no longer sign in to Positron Assistant using a Custom Provider backed by the Kimi/Moonshot OpenAI-compatible API.

The API itself is working correctly. I can call the Kimi/Moonshot API directly with curl or another client, and the same Custom Provider setup works with DeepSeek. However, Positron fails during the sign-in / provider validation step with the following error:

Custom Provider endpoint not found. Check your base URL.

Configuration

Custom Provider base URL:

https://api.moonshot.cn/v1

Also try model override in settings.json but still not work:

{
"positron.assistant.provider.customProvider.enable": true,
"positron.assistant.models.overrides.customProvider": [
{
"name": "Kimi K2.6",
"identifier": "kimi-k2.6"
}
]
}

I also tested other valid Kimi/Moonshot model IDs, but the sign-in step still fails before the model can be used.

Steps to reproduce

1. Open Positron after updating to the latest version.

2. Enable Positron Assistant.

3. Select Custom Provider.

4. Enter the following base URL:

   https://api.moonshot.cn/v1

5. Enter a valid Kimi/Moonshot API key.

6. (Option) Add a model override for kimi-k2.6.

7. Try to sign in or validate the Custom Provider.

Expected behavior

Positron should successfully validate the Custom Provider and allow me to use the configured Kimi/Moonshot model.

Actual behavior

Positron fails during sign-in with:

Custom Provider endpoint not found. Check your base URL.

This error message appears even though the base URL is valid and the API is reachable.

Suspected cause

It looks like the Custom Provider sign-in validation request may be sending an invalid or empty Chat Completions payload, possibly similar to:

{
"model": "",
"messages": []
}

Kimi/Moonshot appears to reject this request because both model and messages must be valid and non-empty. Positron then reports this as an endpoint/base URL error, even though the endpoint itself is valid.

The model override does not appear to be used during the sign-in validation step, so the validation fails before the configured model can be applied.

Why this seems like a Positron regression

• The same Kimi/Moonshot API key and endpoint work outside Positron.
• The base URL format is correct for OpenAI-compatible clients: https://api.moonshot.cn/v1.
• DeepSeek works with the same Custom Provider flow.
• The problem appeared only after updating Positron to the latest version.
• The failure happens during sign-in / validation, before normal chat usage.

Samilar issue #13421