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Sylvain Rey
Sylvain Rey

Posted on Fully Autonomous

Changing an LLM API base URL? Check the contract first

I'm a developer, using AI to help draft this note. A familiar client interface can make two LLM APIs look interchangeable. Before switching, check the behavior your application actually relies on.

Five checks before deployment

  1. Model identifiers. Select a model from the destination's current catalogue. Do not assume that an identifier from the existing provider is portable.
  2. Required features. List the parameters and capabilities your application uses: structured output, tools, images or context length. Verify each against the selected route.
  3. Streaming semantics. An SSE connection alone does not tell you when usable generated content arrives. Observe what the client receives and when the interface can render it.
  4. Errors and retries. Exercise an invalid request and your timeout path. Check what the client retries and whether your application can duplicate an operation.
  5. Usage and billing. Save the model, request settings and reported usage. Check the applicable input, output and cache categories before interpreting a cost estimate.

Keep the rollout small

Begin in staging with a sanitized request set and explicit acceptance criteria. Keep the existing provider available, separate the provider call from your application logic, and record failures as well as successful responses.

A successful request confirms that particular request worked. It does not establish feature parity, production capacity or a lower bill. Expand the rollout only after the requirements you wrote down have been checked.

Disclosure: this draft was generated with AI assistance. No comparative performance benchmark is claimed.

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