[Bug] Error: Provider rejected the request (invalid_request_error, 400): service_tier is not supported

[rdtechie]

Affected area

AI providers and models

What happened?

I've installed prime-agent and logged into GitHub Copilot. I've selected gtp-5.6-luna and then when I tested it I got: Error: Provider rejected the request (invalid_request_error, 400): service_tier is not supported

Steps to reproduce

• Install prime-agent.
• Login to GitHub Copilot.
• Select gtp-5.6-luna (or any other model through GitHub Copilot).
• Chat with the model.

Expected behavior

Model should respond.

Prime Agent version

0.7.2

Environment

macOS Tahoe 26.6.1

Additional context

Looks like there was a fix PR open for it but it got closed: #646

[yanksyoon]

Confirmed this bug and root-caused it. Posting findings plus a ready fix per the contribution process — happy to open the PR if a maintainer invites it.

Root cause. streamOpenAIResponses → buildParams (packages/ai/src/providers/openai-responses.ts) sends service_tier whenever options.serviceTier is defined, and the agent session always defines it (falls back to "default"). GitHub Copilot's endpoints reject the service_tier parameter entirely, so every request to a Responses-API model via the github-copilot provider (e.g. gpt-5.6-luna) fails with the quoted 400.

Verified against the live Copilot Business endpoint with identical /responses payloads:

• with "service_tier": "default" → 400 {"error":{"message":"service_tier is not supported","code":"unsupported_value","param":"service_tier"}}
• without service_tier → 200 OK

Proposed fix (minimal, provider-scoped — other providers still receive the configured tier):

// GitHub Copilot endpoints reject the service_tier parameter entirely
// (400 "service_tier is not supported"), so omit it for Copilot models.
if (options?.serviceTier !== undefined && model.provider !== "github-copilot") {
	params.service_tier = options.serviceTier;
}

Branch with fix + regression test: https://github.com/yanksyoon/prime-agent/tree/fix/copilot-omit-service-tier

The test (packages/ai/test/openai-responses-service-tier.test.ts) mocks the OpenAI client and asserts both directions: service_tier is omitted for github-copilot models and still sent for openai models. Validation: full packages/ai vitest suite passes (329 passed, 0 failed) plus live verification against the Copilot endpoint as above.