> ## Documentation Index
> Fetch the complete documentation index at: https://docs.langchain.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Decision models

> Use SemIf through the LangSmith LLM Gateway for structured classification and scoring with the System One API.

<Note>
  The LLM Gateway is in [beta](/langsmith/release-stages).
</Note>

Decision models return structured answers instead of generated chat messages. Use them through the [LLM Gateway](/langsmith/llm-gateway) to classify text and score it against a rubric. The System One API accepts state and named questions, then returns an answer for each question.

## SemIf

SemIf is a LangChain-hosted decision model with the model ID `semif-qwen3.5-4b`. It is free through September 28, 2026. No provider key or [Gateway Credits](/langsmith/llm-gateway-credits) purchase is required.

### Prerequisites

* Your organization must be on a paid, non-Enterprise [plan](/langsmith/pricing-plans) with SemIf enabled. Availability depends on your organization and region.
* You need a workspace-scoped [LangSmith API key](/langsmith/create-account-api-key) with `gateway:invoke` and `workspaces:read` [permissions](/langsmith/organization-workspace-operations). See [Admin setup](/langsmith/llm-gateway-admin-setup) to grant access.

### Call SemIf

Call `semif-qwen3.5-4b` through `POST /v1/systemone`, not Chat Completions, Messages, or Responses. Set `LANGSMITH_API_KEY` to your workspace-scoped LangSmith API key.

The TypeSafe SDKs append `/v1/systemone` to the base URL. Set `base_url` in Python or `baseURL` in JavaScript to `https://gateway.smith.langchain.com`, without `/v1`.

<Tabs>
  <Tab title="Python">
    Install the TypeSafe SDK:

    ```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    pip install typesafe-sdk
    ```

    ```python theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    import os

    from typesafe_sdk import Noul, TypeSafeClient

    client = TypeSafeClient(
        api_key=os.environ["LANGSMITH_API_KEY"],
        base_url="https://gateway.smith.langchain.com",
    )

    response = client.system_one(
        state="Hello!",
        model="semif-qwen3.5-4b",
        questions={
            "is_helpful": Noul(
                instructions="Does this explain what an LLM gateway does?"
            ),
        },
    )
    ```
  </Tab>

  <Tab title="JavaScript">
    Install the TypeSafe SDK:

    ```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    npm install @typesafe-ai/sdk
    ```

    ```javascript theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    import { noul, TypeSafeClient } from "@typesafe-ai/sdk";

    const client = new TypeSafeClient({
      apiKey: process.env.LANGSMITH_API_KEY,
      baseURL: "https://gateway.smith.langchain.com",
    });

    const response = await client.systemOne({
      state: "Hello!",
      model: "semif-qwen3.5-4b",
      questions: {
        is_helpful: noul("Does this explain what an LLM gateway does?"),
      },
    });
    ```
  </Tab>

  <Tab title="cURL">
    ```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    curl https://gateway.smith.langchain.com/v1/systemone \
        -H "Authorization: Bearer $LANGSMITH_API_KEY" \
        -H "Content-Type: application/json" \
        -d '{
          "state": "Hello!",
          "model": "semif-qwen3.5-4b",
          "questions": {
            "is_helpful": {
              "type": "noul",
              "instructions": "Does this explain what an LLM gateway does?"
            }
          }
        }'
    ```
  </Tab>
</Tabs>

Pass the text to evaluate in `state` and between 1 and 32 named questions in `questions`. SemIf supports three question types:

* **`noul`**: Returns the probability that the answer is true.
* **`choice`**: Classifies the state into one of the supplied options.
* **`score`**: Scores the state against a rubric.

The response contains `answers` keyed by question name rather than a chat message. Streaming is not supported.

You can also select SemIf from the hosted models on the gateway home page to get a request example. For regional base URLs, see [Regional gateways](/langsmith/llm-gateway-direct-model-access#use-a-regional-gateway).

### Apply gateway policies

SemIf calls do not consume Gateway Credits. Gateway [access](/langsmith/llm-gateway-model-access-policies), [rate-limit](/langsmith/llm-gateway-rate-limit-policies), and [budget policies](/langsmith/llm-gateway-spend-policies) still apply.

## TypeSafe

The gateway also supports TypeSafe decision models with bring-your-own-key (BYOK). Configure `TYPESAFE_API_KEY` as a workspace [provider secret](/langsmith/llm-gateway-admin-setup#1-add-provider-secrets). See [TypeSafe setup](/oss/python/integrations/providers/typesafe#setup) to create a key and install the LangChain integration.

Set `LANGSMITH_API_KEY` to your workspace-scoped LangSmith API key. The `typesafe/` prefix routes the request through your workspace's TypeSafe provider secret, not the hosted SemIf model. Do not pass your TypeSafe API key as the SDK's `api_key` or `apiKey` when calling the gateway. Use the gateway base URL without `/v1` for the SDKs:

<Tabs>
  <Tab title="Python">
    Install the TypeSafe SDK:

    ```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    pip install typesafe-sdk
    ```

    ```python theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    import os

    from typesafe_sdk import Noul, TypeSafeClient

    client = TypeSafeClient(
        api_key=os.environ["LANGSMITH_API_KEY"],
        base_url="https://gateway.smith.langchain.com",
    )

    response = client.system_one(
        state="Hello!",
        model="typesafe/jev-1.13.0",
        questions={
            "is_helpful": Noul(
                instructions="Does this explain what an LLM gateway does?"
            ),
        },
    )
    ```
  </Tab>

  <Tab title="JavaScript">
    Install the TypeSafe SDK:

    ```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    npm install @typesafe-ai/sdk
    ```

    ```javascript theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    import { noul, TypeSafeClient } from "@typesafe-ai/sdk";

    const client = new TypeSafeClient({
      apiKey: process.env.LANGSMITH_API_KEY,
      baseURL: "https://gateway.smith.langchain.com",
    });

    const response = await client.systemOne({
      state: "Hello!",
      model: "typesafe/jev-1.13.0",
      questions: {
        is_helpful: noul("Does this explain what an LLM gateway does?"),
      },
    });
    ```
  </Tab>

  <Tab title="cURL">
    ```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    curl https://gateway.smith.langchain.com/v1/systemone \
        -H "Authorization: Bearer $LANGSMITH_API_KEY" \
        -H "Content-Type: application/json" \
        -d '{
          "state": "Hello!",
          "model": "typesafe/jev-1.13.0",
          "questions": {
            "is_helpful": {
              "type": "noul",
              "instructions": "Does this explain what an LLM gateway does?"
            }
          }
        }'
    ```
  </Tab>
</Tabs>

## See also

* [Admin setup](/langsmith/llm-gateway-admin-setup): Grant gateway access without configuring a provider secret for SemIf.
* [TypeSafe integration](/oss/python/integrations/providers/typesafe): Use TypeSafe decision models through LangChain.

***

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