Decision models

Decision models classify or score text and return structured answers instead of generated chat messages. Call them through the LLM Gateway with the System One API. LangSmith provides an open source decision model, SemIf (semif-qwen3.5-4b), through the gateway for free through September 28, 2026.

SemIf is enabled for US organizations on Free, Developer, and Plus plans.

Quickstart

Set your LangSmith API key:

export LANGSMITH_API_KEY="<your-api-key>"

Then run a request:

Python
JavaScript
cURL

Install the TypeSafe SDK:

pip install typesafe-sdk

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?"
        ),
    },
)

Install the TypeSafe SDK:

npm install @typesafe-ai/sdk

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?"),
  },
});

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?"
        }
      }
    }'

Understand decision models

Pass the text to evaluate in state and between 1 and 32 named questions in questions. Decision models support 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.

SemIf

You can select SemIf from the hosted models on the gateway home page to get a request example. For regional base URLs, see Regional gateways. SemIf calls do not consume Gateway Credits. Gateway access, rate-limit, and budget policies still apply.

TypeSafe (Jev)

The gateway also supports TypeSafe decision models with bring-your-own-key (BYOK). Configure TYPESAFE_API_KEY as a workspace provider secret. See 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:

Python
JavaScript
cURL

Install the TypeSafe SDK:

pip install typesafe-sdk

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?"
        ),
    },
)

Install the TypeSafe SDK:

npm install @typesafe-ai/sdk

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?"),
  },
});

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?"
        }
      }
    }'

Core capabilities

Administration and governance

Advanced

Quickstart

Understand decision models

SemIf

TypeSafe (Jev)

See also

​Quickstart

​Understand decision models

​SemIf

​TypeSafe (Jev)

​See also

Quickstart

Understand decision models

SemIf

TypeSafe (Jev)

See also