vLLM/docs/serving/online_serving/structured_decisions.md

# Structured Decisions

The `/v1/systemone` endpoint answers a set of typed questions about a state and
returns a probability for every allowed answer.

The endpoint is available by default on generation models. Models without a
supported read strategy return 501. Supported architectures require
`--logprobs-mode raw_logprobs` or `processed_logprobs`, since `label_mass` needs
log probabilities.

## How it works

1. Each question is one read. The user message is the state, followed by the
   question and its options with the type's labels, and an instruction to
   answer with one label.
2. The read is the reply's first token. Each label must be one token there,
   or the request returns 400.
3. The read returns the logprobs of that question's label tokens. Softmax over
   the labels gives the answer's probabilities.

Thinking is off unless `chat_template_kwargs` turns it on.

Probabilities can differ between identical requests. They depend on which
requests share a batch and on whether a read hits the prefix cache. Set
`VLLM_BATCH_INVARIANT=1` for reads that repeat exactly, at a cost in
throughput.

Every read of a request starts with the state, so with
`--enable-prefix-caching` the state is prefilled once and each further
question prefills only its own text, then reads one token.

## Question types

| type | criteria | answer |
| --- | --- | --- |
| `choice` | map of option name to a description or `null` | `choice`, `probabilities` by option name, `confidence` |
| `noul` | `null`, or an object with optional `true` and `false` descriptions | `noul` (probability of yes), `probabilities`, `confidence` |
| `score` | ordered list of level names | `score` (expected 0-indexed level), `legend`, `probabilities` by level index, `confidence` |

A choice has at least one option, a score at least two levels. A question id
is a non-empty string.

## Example

```bash
curl -s http://localhost:8000/v1/systemone \
  -H "Content-Type: application/json" \
  -d '{
    "model": "Qwen/Qwen3-0.6B",
    "state": {"ticket": "My card was charged twice for one order."},
    "questions": {
      "team": {
        "type": "choice",
        "instructions": "Which team should handle this ticket?",
        "criteria": {
          "billing": "payments and refunds",
          "shipping": "deliveries",
          "security": "account access"
        }
      },
      "urgent": {
        "type": "noul",
        "instructions": "Does the customer need a reply within the hour?",
        "criteria": {"true": "the account is locked or money is moving"}
      },
      "tone": {
        "type": "score",
        "instructions": "How upset is the customer?",
        "criteria": ["calm", "annoyed", "furious"]
      }
    },
    "chat_template_kwargs": {"enable_thinking": false}
  }'
```

Response, with probabilities that depend on the model:

```json
{
  "id": "decision-...",
  "object": "structured_decision",
  "created": 1790000000,
  "model": "Qwen/Qwen3-0.6B",
  "answers": {
    "team": {
      "type": "choice",
      "choice": "billing",
      "probabilities": {"billing": 0.97, "shipping": 0.01, "security": 0.02},
      "confidence": 0.90
    },
    "urgent": {
      "type": "noul",
      "noul": 0.02,
      "probabilities": {"yes": 0.02, "no": 0.98},
      "confidence": 0.95
    },
    "tone": {
      "type": "score",
      "score": 0.6,
      "legend": {"0": "calm", "1": "annoyed", "2": "furious"},
      "probabilities": {"0": 0.7, "1": 0.2, "2": 0.1},
      "confidence": 0.65
    }
  },
  "usage": {"input_tokens": 142, "output_tokens": 3},
  "diagnostics": {
    "team": {"label_mass": 0.93, "argmax_is_label": true},
    "urgent": {"label_mass": 0.98, "argmax_is_label": true},
    "tone": {"label_mass": 0.91, "argmax_is_label": true}
  }
}
```

`diagnostics.label_mass` is the probability the model put on the labels across
its whole vocabulary. A low value means most of the probability went to tokens
that are not labels. `confidence` is the chosen option's probability over the
whole vocabulary: its share of the labels times `label_mass`.

## Labels

Labels follow the type: a `choice` labels its options `A` to `Z` in the order
the request lists them, a `noul` labels its options `yes` and `no`, and a
`score` labels its levels `0` to `9`, so a level's label is its score.

## Limits

| limit | value |
| --- | --- |
| questions per request | 64 |
| options per `choice` | 26 |
| levels per `score` | 10 |

## Clef-Flash

[Clef-Flash](https://huggingface.co/Cloudflare/clef-flash) uses a Qwen3.5-9B
backbone and a joint schema head to score all questions in one forward pass.
vLLM detects the head and serves the checkpoint as a pooling model.

```bash
vllm serve Cloudflare/clef-flash --max-model-len 16384
```

Send requests to `/v1/systemone` using `state` and `questions`, as in the
examples above. `choice`, `noul` and `score` questions are supported.

- Text and JSON states use the checkpoint's fixed prompt. JSON is compact
  with sorted keys. `instructions` returns 400; `chat_template_kwargs`
  has no effect.
- The state is truncated to fit 16,384 tokens, or `max_model_len` if smaller.
  A schema that exceeds this bound returns 400.
- `images` and `videos` are placed before the state. Videos are sampled at
  2 fps and processed by the Qwen3.5 vision processor. Audio inputs return
  400, and video soundtracks are ignored.
- Each request performs one pooling read. `usage.input_tokens` counts the
  prompt once, `output_tokens` is 0, and `label_mass` is 1.

## Clef-Omni

[Clef-Omni](https://huggingface.co/Cloudflare/clef-omni) is a decision model:
a joint schema head on the Qwen3-Omni thinker scores every option of every
question in one forward pass. vLLM serves it as a pooling model.

```bash
vllm serve Cloudflare/clef-omni
```

- A request is one read. The prompt is the one the checkpoint's
  `joint_schema_model.py` builds: the state, then every question with its
  options. A JSON state is written as compact JSON with sorted keys.
- A state too long for the model is truncated to fit, as the reference does.
  A request whose questions alone exceed 64,000 tokens, or `max_model_len`,
  returns 400.
- `instructions` returns 400, since the prompt is fixed. `chat_template_kwargs`
  has no effect.
- There are no labels, so `label_mass` is 1 and `confidence` is the chosen
  option's probability. `usage.input_tokens` counts the prompt once, and
  `output_tokens` is 0.
- `images`, `audio` and `videos` are read as the reference does: placed
  before the state, videos sampled at 2 fps, and a video's soundtrack heard
  with it when every video has one. Audio clips cannot be sent together with
  videos that have soundtracks.

## Liquid d1

[`LiquidAI/d1-3B`](https://huggingface.co/LiquidAI/d1-3B) is LFM2.5-VL-3B
post-trained to answer decisions as the first token of its reply. vLLM serves
it as a generative model.

```bash
vllm serve LiquidAI/d1-3B
```

- The server writes the prompt and reads the label tokens the way the
  `prompt.py` shipped with the checkpoint does, so picks and probabilities
  match `model.system_one()`. `confidence` and `usage` follow the definitions
  on this page instead.
- A JSON state is written as indented JSON. A `null` state leaves the images,
  or the question alone, as the prompt.
- `images` are placed before the state and shrunk to at most 1024 x 1024
  pixels, as the reference does.
- A `choice` whose option names are all single letters is labeled with those
  letters.
- When each request carries one question over a state that changes from
  request to request, `--no-enable-prefix-caching` lowers latency.

## Request fields

| field | meaning |
| --- | --- |
| `state` | what the questions are about: a string, or JSON that is sent as its JSON text |
| `questions` | question id to `{type, instructions, criteria}`, asked in this order |
| `instructions` | optional context placed ahead of the questions |
| `chat_template_kwargs` | passed to the chat template, for example `{"enable_thinking": false}` |
| `cache_salt` | optional [prefix-cache salt](../../usage/security.md#cache-salting) applied to every question |
| `images`, `audio`, `videos` | optional media URLs or data URLs, for models that take them ([Clef-Flash](#clef-flash), images/video; [Clef-Omni](#clef-omni); [Liquid d1](#liquid-d1), images only) |

A question with any field other than `type`, `instructions` and `criteria` is
rejected with a 400.

When [tracing](../../../examples/observability/opentelemetry/README.md) is enabled
with `--otlp-traces-endpoint`, the HTTP `traceparent` and `tracestate` headers are
forwarded to every question's generation request.