# CPU stand-in for development

> Serve every route from a small model on the CPU, to build against the API anywhere.

Source: https://opendecisio.com/docs/quickstart/cpu-stand-in/

The stand-in serves the same routes from a small model, so you can develop and test a client without a card. It is not the measured system, and its answers are not for measurement.

 

[Figure: Every route, from a small model on the CPU, so you can build against the API anywhere. The CPU stand-in: install with the development tools, run the unit tests, start the server with --backend hf on Qwen/Qwen3-0.6B-Base. It serves every route, and it is for development, not measurement.]

 

## TL;DR

 

```
uv sync --extra dev --frozen
uv run pytest
uv run python -m decisio.serve.vllm_engine --backend hf --model Qwen/Qwen3-0.6B-Base
```

 

Run against the CPU stand-in at v0.11.1 on 2026-10-14: the install and the server start; the unit tests passed in decisio's own CI on this commit.

 

The commands on these pages that the stand-in can serve are run against it.

  

| Word | Meaning |
| --- | --- |
| stand-in | `--backend hf`: every route, from `Qwen/Qwen3-0.6B-Base` on the CPU |
| unit tests | `uv run pytest`, which runs on any machine; the GPU tests need a card |

 

## What it is, and is not

 

```
uv sync --extra dev --frozen
uv run pytest
uv run python -m decisio.serve.vllm_engine --backend hf --model Qwen/Qwen3-0.6B-Base
```

 

Run against the CPU stand-in at v0.11.1 on 2026-10-14: the install and the server start; the unit tests passed in decisio's own CI on this commit.

 

- `uv run pytest` runs the unit tests on any machine; the GPU tests (`pytest -m gpu`) need a card, and run by hand until a nightly GPU runner is registered.
- `--backend hf` serves every route from a small Hugging Face model on the CPU, for developing and testing the routes; it is not the measured system and its answers are not for measurement.
- CI runs the stand-in on `Qwen/Qwen3-0.6B-Base` at a pinned revision (`STAND_IN_REVISION` in `.github/workflows/ci.yml`).
- [`examples/tasks/`](https://github.com/aminry/decisio/tree/v0.11.1/examples/tasks) walks through task registration against it.

 

## What next

 

- [Get started](https://opendecisio.com/docs/): send a first question to it.
- [Teach it your question](https://opendecisio.com/docs/tasks/): the walk-through that runs on a laptop against the stand-in.
- [Choose your machine](https://opendecisio.com/docs/quickstart/): the paths that run the real bases.