---
title: Coming from Jev
description: Change the base URL, keep the request. What is the same, what is extra, what to watch.
icon: arrow-right-left
sidebar:
  label: Migrate your integration
---

aityx implements the Jev `systemone` contract. An integration that calls
`POST https://api.typesafe.ai/v1/systemone` works against `POST https://api.aityx.ai/v1/systemone` with a new key.

1. **Point the client at aityx**

    ```bash curl
    curl https://api.aityx.ai/v1/systemone \
      -H "Authorization: Bearer $AITYX_API_KEY" \
      -H "Content-Type: application/json" \
      -d @request.json
    ```

    ```js fetch
    const res = await fetch("https://api.aityx.ai/v1/systemone", {
      method: "POST",
      headers: { Authorization: `Bearer ${process.env.AITYX_API_KEY}`, "Content-Type": "application/json" },
      body: JSON.stringify({ model: "jev-latest", state, questions }),
    });
    const { answers, model, receipt } = await res.json();
    // Keep the complete model and receipt in your own application.
    ```

    ```python requests
    import os, requests

    res = requests.post(
        "https://api.aityx.ai/v1/systemone",
        headers={"Authorization": f"Bearer {os.environ['AITYX_API_KEY']}"},
        json={"model": "jev-latest", "state": state, "questions": questions},
    )
    result = res.json()
    answers, model, receipt = result["answers"], result["model"], result["receipt"]
    # Keep the complete model and receipt in your own application.
    ```

2. **Expect the first call to be slower**

    With a `jev-*` model name, the first request for a given set of questions builds a decision model. It takes
    seconds. Later requests may reuse the model from a temporary cache, improving latency. Every questions-based
    call uses System Two pricing, including cache hits. The cache can expire or be evicted.

3. **Keep and submit the decision model**

    The response's `model` is the complete decision definition and its questions. Save that object, then send it
    with each new state:

    ```js
    body: JSON.stringify({ model, state })
    ```

    Matching JSON then uses System One pricing, with output free. The model in the request contributes to input
    billing. This removes generation from execution and makes the rules you reviewed repeatable.

4. **Add what Jev could not do**

    Add `number` and `date` questions where you were computing in code. Keep `noul`, `choice` and `score` as they
    are.

## What is the same

- Request shape: `model`, `state` (string or JSON), `questions` keyed by id.
- Question types `noul`, `choice`, `score`, with `instructions` and `criteria`. Aliases `options` and `levels`.
- Answer fields `noul`, `choice`, `score`, `confidence` and `probabilities`, with `answers` keyed by question id.
- Usage information and bearer authentication.

## What is extra

- Question types `number` and `date`.
- A portable `model` object and the complete execution `receipt` in the response.
- The response `model` is a definition, rather than Jev’s inference-model name. Check clients that expect a string.
- `cache_hit`, `provider_usage` and `billing` distinguish reuse, actual AI work and customer charges.
- `score` answers also carry `level`, the most likely level by name.

## What to watch

| In Jev | In aityx |
|---|---|
| Your integration may use confidence thresholds to route a result. | Review those thresholds: with matching structured inputs, one option has probability 1. See [Determinism and confidence](/docs/concepts/determinism-and-confidence). |
| A missing fact does not stop the call. | A missing required fact fails with `400 invalid_state` before execution. Use `blank` only when your policy permits absence; otherwise supply the missing fact. |
| `model: jev-1.13.0` pins a model version. | A `jev-*` name selects the generator; submit the returned definition to keep the rules fixed. |
| Arithmetic, counting and date comparison happen in your code. | Put them in `number` and `date` questions; the engine computes them. |
| State is text or JSON. | Matching JSON plus a full model skips the reader. Text or unresolved fields may add an extraction charge. Questions-based calls remain at System Two rates. |

Models and receipts are yours to retain. The preview does not provide durable model storage or receipt
history. See [Models](/docs/concepts/models) and [Receipts](/docs/concepts/receipts).