Create an experiment

import requests

url = "https://app.langwatch.ai/api/v1/experiment/init"

payload = {}
headers = {
    "X-Auth-Token": "<api-key>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {'X-Auth-Token': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({})
};

fetch('https://app.langwatch.ai/api/v1/experiment/init', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "slug": "<string>",
  "path": "<string>"
}

This response has no body data.

This response has no body data.

This response has no body data.

This response has no body data.

This response has no body data.

Experiments

Create an experiment

Create an experiment, or return the existing one when the slug is already taken. This is the first call in an experiment run: take the slug back, report results against it, and every run under that slug groups together in the app. The SDKs call this endpoint for you. The body carries experiment_type and at least one of experiment_slug (the stable slug you choose, which is what makes repeated runs land together) or experiment_id; experiment_name names it on creation and workflowId ties it to an Optimization Studio workflow.

POST

api

experiment

init

Create an experiment

import requests

url = "https://app.langwatch.ai/api/v1/experiment/init"

payload = {}
headers = {
    "X-Auth-Token": "<api-key>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {'X-Auth-Token': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({})
};

fetch('https://app.langwatch.ai/api/v1/experiment/init', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "slug": "<string>",
  "path": "<string>"
}

This response has no body data.

This response has no body data.

This response has no body data.

This response has no body data.

This response has no body data.

Authorizations

X-Auth-Token

string

header

required

Project API key for sending traces and accessing project-scoped resources. Format: sk-lw-... (no underscore). Obtain one by creating a project via the Admin API or the LangWatch UI.

Body

application/json

experiment_type

enum<string>

required

Available options:

DSPY,

BATCH_EVALUATION,

BATCH_EVALUATION_V2

experiment_id

string | null

experiment_slug

string | null

experiment_name

string

workflowId

string

Response

Success

slug

string

required

Slug of the experiment, created or existing

path

string

required

Path to the experiment in the LangWatch app

Last modified on October 12, 2026