Claude models fail with HTTP 400 in Visual Studio while GPT-5.4 and Gemini work

[al-allanic]

🏷️ Discussion Type

Bug

💬 Feature/Topic Area

Copilot in GitHub

Body

In Visual Studio, all Claude models fail immediately with “There was a problem completing your request”. GPT-5.4 and Gemini 2.5 Pro work in the same session and account. Output log shows repeated HTTP 400 Bad Request from /chat/completions.
I have been working with Sonnet 4.6 for weeks now. Yesterday, I got for the first time a “rate-limiter” killing my requests mid-sentence. Sonnet 4.6 said it was probably caused by the specific taks he was doing (fixing hundreds of warnings in an old C# file). He tried to resume several times, being killed quickly. He said there was probably a sliding time window, which needed to be waited out, so I stopped working for 12 hours. Now, not even a ping can reach any Claude model, from Haiku to Opus, but other model vendors (premium or standard) are unaffected

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