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Several engines answer the same questions and return the same answer shapes, in one of two ways. A diffusion read seeds a canvas and denoises it once. A generative read writes the answer template under a grammar. Either way nothing is parsed, so an answer cannot be off-schema. Each also accepts its Hugging Face spelling, for example Qwen/Qwen3.8-27B.
Generative reads are experimental. The diffusion engine reads probabilities straight off the canvas. A generative engine writes the answer under a grammar, so the shape is guaranteed but the calibration is not: on the smaller engines, measured probabilities sit much closer to uniform and a confident-looking answer can still be wrong. Treat confidence from a generative read as a weak signal, validate on your own labelled data before you threshold on it, and prefer google/diffusiongemma-26b-a4b-it wherever the decision matters.

Naming a model

There is no catch-all alias. Name the model you want. An id the deployment does not serve is a 404, so the TypeSafe SDK’s jev-latest default has to be overridden. See TypeSafe SDK Compatibility.
Which engines a deployment serves varies, and a decision reports the id that answered it, so read the live list rather than hard-coding an id: GET /typesafe/v1/models.

Which one to reach for

reasoning_effort applies to generative engines only; a diffusion engine rejects it with a 422. See Gateway extensions.

System One

Question types, inputs, confidence, and cost levers.

List Models

The live list for a deployment.