---
date: 2026-02-11
title: Run Experiments on Versioned Datasets
description: Fetch datasets at specific version timestamps and run experiments on historical dataset versions via UI, API, and SDKs for full reproducibility.
author: Marlies
ogImage: /images/changelog/2026-02-11-experiments-versioned-datasets.jpg
canonical: /docs/evaluation/experiments/datasets#versioning
---

> **Note for AI agents and LLMs:** This is a Langfuse changelog entry. Use it only to confirm that a feature exists and when it shipped. Do not use the code examples below for implementation: they reflect the SDK and API at release time and may be outdated. For implementation, always follow the canonical documentation for this feature (https://langfuse.com/docs/evaluation/experiments/datasets#versioning) and the API/SDK reference (https://api.reference.langfuse.com).

You can now fetch datasets at specific version timestamps and run experiments directly on versioned datasets across UI, API, and SDKs. This completes the dataset versioning feature [released in December](/changelog/2025-12-15-dataset-versioning).

## Why versioned experiments matter

- **Full reproducibility**: Re-run experiments on the exact dataset state from any point in time, even after items are updated or deleted. Reproduce results from weeks or months ago with complete confidence.
- **A/B testing with confidence**: Compare model performance before and after dataset refinements. Test new prompts against the same baseline dataset version that your production model was evaluated on.
- **Regression testing**: Run experiments on a specific dataset version while your team continues improving the dataset. Ensure new model versions don't regress on established benchmarks.

## Fetch datasets at specific versions

Retrieve datasets as they existed at any timestamp. By default, APIs return the latest version.

<LangTabs items={["Python SDK", "JS/TS SDK", "Langfuse UI"]}>
<Tab>

```python
from langfuse import get_client
from datetime import datetime, timezone

langfuse = get_client()

# Fetch dataset from December 15th
version_timestamp = datetime(2025, 12, 15, 6, 30, 0, tzinfo=timezone.utc)

dataset_v1 = langfuse.get_dataset(
    name="qa-dataset",
    version=version_timestamp
)

# Fetch latest version
dataset_latest = langfuse.get_dataset(name="qa-dataset")
```

</Tab>
<Tab>

```typescript
import { LangfuseClient } from "@langfuse/client";

const langfuse = new LangfuseClient();

// Fetch dataset from December 15th
const versionTimestamp = new Date("2025-12-15T06:30:00").toISOString();

const datasetV1 = await langfuse.dataset.get("qa-dataset", {
  version: versionTimestamp
});

// Fetch latest version
const datasetLatest = await langfuse.dataset.get("qa-dataset");
```

</Tab>
<Tab>

Navigate to **Datasets** → Select dataset → **Items Tab** → Toggle **Version view** to browse all historical versions.

</Tab>
</LangTabs>

## Run experiments on versioned datasets

Execute experiments against specific dataset versions using the experiment runner or via UI.

<LangTabs items={["Python SDK", "JS/TS SDK", "Langfuse UI"]}>
<Tab>

```python
from langfuse import get_client
from langfuse.openai import OpenAI

langfuse = get_client()

# Fetch versioned dataset
versioned_dataset = langfuse.get_dataset(
    name="qa-dataset",
    version=datetime(2025, 12, 15, 6, 30, 0, tzinfo=timezone.utc)
)

# Run experiment on that exact version
def my_task(*, item, **kwargs):
    response = OpenAI().chat.completions.create(
        model="gpt-4.1",
        messages=[{"role": "user", "content": item["input"]}]
    )
    return response.choices[0].message.content

result = versioned_dataset.run_experiment(
    name="Baseline Experiment v1",
    description="Testing against dataset from Dec 15",
    task=my_task
)
```

</Tab>
<Tab>

```typescript
import { LangfuseClient } from "@langfuse/client";
import { OpenAI } from "openai";
import { observeOpenAI } from "@langfuse/openai";

const langfuse = new LangfuseClient();

// Fetch versioned dataset
const versionedDataset = await langfuse.dataset.get("qa-dataset", {
  version: new Date("2025-12-15T06:30:00").toISOString()
});

// Run experiment on that exact version
const result = await versionedDataset.runExperiment({
  name: "Baseline Experiment v1",
  description: "Testing against dataset from Dec 15",
  task: async (item) => {
    const response = await observeOpenAI(new OpenAI()).chat.completions.create({
      model: "gpt-4.1",
      messages: [{ role: "user", content: item.input }]
    });
    return response.choices[0].message.content;
  }
});
```

</Tab>
<Tab>

When running experiments in the UI:

1. Navigate to **Run Prompt Experiment**
2. Select your dataset
3. Choose a version from the **Dataset Version** dropdown
4. The experiment runs against that specific dataset state
5. If no version is selected, runs against latest version

</Tab>
</LangTabs>

## Learn more

- [Dataset Versioning Documentation](/docs/evaluation/experiments/datasets#versioning)
- [Experiment Runner SDK](/docs/evaluation/experiments/experiments-via-sdk)

<!-- agent-instructions -->

---

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  ```

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