Grok 4.1 Fast, best tool-calling model with a 2M context window

Grok 4.1 Fast and Agent Tools API
Bringing the next generation of tool-calling agents to the xAI API

Today, we’re excited to launch two powerful new additions to the xAI API:

Grok 4.1 Fast, our best tool-calling model with a 2M context window. It reasons and completes agentic tasks accurately and rapidly, excelling at complex real-world use cases such as customer support and finance.
The Agent Tools API, which gives agents access to real-time X data, web search, remote code execution, and more.
Paired together, Grok 4.1 Fast and the Agent Tools API empower developers to build production-grade agents that specialize in tool calling and agentic search.

Trained for the real world
We built Grok 4.1 Fast specifically for real-world enterprise use cases.

Through RL training in simulated environments, Grok 4.1 Fast was exposed to a a wide variety of tools covering dozens of domains. This diverse training gives Grok 4.1 Fast exceptional performance on τ²-bench Telecom, a challenging benchmark that evaluates agentic tool use in real-world customer support scenarios.

State-of-the-art tool calling
As developers build increasingly capable autonomous agents that plan over long horizons and operate independently, models must deliver intelligence without compromising speed and cost.

Grok 4.1 Fast is our answer: a model that combines frontier tool-calling performance with blazing-fast inference and cost effectiveness.

Agent Tools API
We’re also launching the Agent Tools API, a suite of powerful server-side tools that allow Grok 4.1 Fast to operate as a fully autonomous agent.

With just a few lines of code, developers can enable Grok to browse the web, search X posts, execute code, retrieve uploaded documents, and more.

These tools run entirely on xAI’s infrastructure, so developers no longer need to manage API keys, rate limits, sandboxes, or retrieval pipelines. Grok decides when and how to use them, often invoking multiple tools in parallel across several turns, until it has everything it needs to deliver a final answer.

A full-featured toolset
The Agent Tools API is a versatile suite that lets you significantly extend the capabilities of our base Grok models.

The best agent for deep research
Real-time information retrieval and deep research are core strengths of Grok 4.1 Fast. With our native integration into the X ecosystem and powerful web-browsing capabilities, search agents powered by the xAI API are state-of-the-art on challenging agentic search benchmarks.

Grok 4.1 Fast sets a new standard in factuality, cutting the hallucination rate in half compared to Grok 4 Fast while still delivering performance on par with Grok 4 when evaluated on FActScore.

Start Building
We’re releasing two variants of Grok 4.1 Fast on the API:

• grok-4-1-fast-reasoning for maximal intelligence
• grok-4-1-fast-non-reasoning for instant responses

For the next two weeks, our models and tools will be free on select platforms:

We’ve partnered with OpenRouter to make the Grok 4.1 Fast models available for free.
We’re offering all agentic tools via the xAI Agent Tools API completely free.