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Serving

Cold start

What is cold start?

A cold start is the delay on the first request to an endpoint with no resident replica: capacity must be acquired, the model weights loaded and the runtime initialised. It is dominated by weight loading, so it scales with model size.

The user-visible effect is one very slow request followed by normal ones, which is a distinctive and easily misdiagnosed pattern in latency graphs.

The mitigations are keeping a minimum replica warm, choosing a smaller model, or accepting it where the caller is a batch process that does not care. Adapter-based serving helps too: loading a small adapter against an already-resident base is far quicker than loading a whole model.

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