# Experiment

URL: https://docs.hanzo.ai/docs/openapi/experiment

> A/B testing anything: a flag, an ad, a subject line, a model.

Also for this capability: **API** · [CLI](https://docs.hanzo.ai/docs/cli/experiment) · [MCP](https://docs.hanzo.ai/docs/mcp-tools/experiment) · [SDKs](https://docs.hanzo.ai/docs/sdks)

A/B testing anything: a flag, an ad, a subject line, a model.

> [All API references →](https://docs.hanzo.ai/docs/openapi) · [Get started →](https://docs.hanzo.ai/docs/guides)

|                |                                        |
| -------------- | -------------------------------------- |
| **Base URL**   | `https://api.hanzo.ai`                 |
| **Operations** | 7                                      |
| **Auth**       | `Authorization: Bearer $HANZO_API_KEY` |

## Specification

Specification pending — no HIP in [hanzoai/hips](https://github.com/hanzoai/hips) declares `capability: experiment` yet. What this capability serves is below, from the API document; what it is — the store it owns, how it meters, what it publishes — is written as a HIP under HIP-0139.

## Four surfaces

| Surface  | Reaches this capability as                         | Coverage                                                                  |
| -------- | -------------------------------------------------- | ------------------------------------------------------------------------- |
| **REST** | `experiment` at its own prefix                     | 7 operations                                                              |
| **CLI**  | `hanzo experiment …`                               | 7 of 7                                                                    |
| **SDK**  | `ExperimentApi` in every published client          | 7 methods                                                                 |
| **MCP**  | tool `experiment` on `https://api.hanzo.ai/v1/mcp` | 7 operations, 2 under the document's own id — ask `describe` for the rest |

## Quickstart

```bash
export HANZO_API_KEY=sk-...   # console.hanzo.ai → API keys
```

Then the first call — a read that needs nothing but the key. `GET /v1/experiment`, operation `get_experiment`:

**CLI**

```bash
hanzo experiment list
```

**SDK**

**.ts**

```ts
import { Configuration, ExperimentApi } from 'hanzoai';

const api = new ExperimentApi(new Configuration({ accessToken: process.env.HANZO_API_KEY }));
const { data } = await api.getExperiment();
```

**.py**

```python
from hanzoai.cloud import ApiClient, Configuration
from hanzoai.cloud.api import ExperimentApi

client = ApiClient(Configuration(access_token=os.environ["HANZO_API_KEY"]))
result = ExperimentApi(client).get_experiment()
```

**.go**

```go
cfg := hanzoai.NewConfiguration()
cfg.AddDefaultHeader("Authorization", "Bearer "+os.Getenv("HANZO_API_KEY"))
client := hanzoai.NewAPIClient(cfg)

resp, _, err := client.ExperimentAPI.GetExperiment(context.Background()).Execute()
if err != nil {
	return err
}
```

**.rs**

```rust
use hanzo_client::apis::{configuration::Configuration, experiment_api};

let mut cfg = Configuration::new();
cfg.bearer_access_token = std::env::var("HANZO_API_KEY").ok();

let result = experiment_api::get_experiment(&cfg, Default::default()).await?;
```

**.java**

```java
import ai.hanzo.cloud.ApiClient;
import ai.hanzo.cloud.api.ExperimentApi;

ApiClient client = new ApiClient();
client.setBearerToken(System.getenv("HANZO_API_KEY"));

var result = new ExperimentApi(client).getExperiment();
```

**HTTP**

```bash
curl https://api.hanzo.ai/v1/experiment \
  -H "Authorization: Bearer $HANZO_API_KEY"
```

**MCP**

MCP reaches **experiment** through the `experiment` tool, which names its 7 operations with its own verbs — this one among them, under a name only MCP declares. `describe` explains any of them:

```bash
curl -X POST https://api.hanzo.ai/v1/mcp \
  -H "Content-Type: application/json" \
  -d '{
       "jsonrpc": "2.0",
       "id": 1,
       "method": "tools/call",
       "params": {
         "name": "describe",
         "arguments": {
           "op": "list_experiments"
         }
       }
     }'
```

Answers `200` with `object` — ok.

## Endpoints

| Endpoint                                                                                                          | What it does                                                                                                                                                                                                                               |
| ----------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| [`POST /v1/experiment/{id}/analyze`](https://docs.hanzo.ai/docs/openapi/experiment/post-experiment-by-id-analyze) | Per-variant conversion, lift and statistical significance against the control arm.                                                                                                                                                         |
| [`GET /v1/experiment/{id}/assign`](https://docs.hanzo.ai/docs/openapi/experiment/get-experiment-by-id-assign)     | The variant one subject is bucketed into, and the payload that variant carries.                                                                                                                                                            |
| [`POST /v1/experiment/{id}/decide`](https://docs.hanzo.ai/docs/openapi/experiment/post-experiment-by-id-decide)   | Promotes one variant to the whole rollout and records who decided.                                                                                                                                                                         |
| [`GET /v1/experiment/{id}`](https://docs.hanzo.ai/docs/openapi/experiment/get-experiment-by-id)                   | One experiment's definition and lifecycle: variants, weights, control arm, status and winner.                                                                                                                                              |
| [`GET /v1/experiment/health`](https://docs.hanzo.ai/docs/openapi/experiment/get-experiment-health)                | Whether the experiments subsystem is mounted and serving in this process.                                                                                                                                                                  |
| [`GET /v1/experiment`](https://docs.hanzo.ai/docs/openapi/experiment/get-experiment)                              | Every experiment in the caller's org, with its variants, status and decision, ordered by project then id.                                                                                                                                  |
| [`POST /v1/experiment`](https://docs.hanzo.ai/docs/openapi/experiment/post-experiment)                            | Registers a controlled experiment AND puts its assignment flag live, in that order, so the arms start bucketing subjects the moment this returns 201 — the flag is created active at 100% rollout, with each variant weighted as declared. |

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