Grok 4 Fast | xAI

We’re thrilled to present Grok 4 Fast, our latest advancement in cost-efficient reasoning models. Built on xAI’s learnings from Grok 4, Grok 4 Fast delivers frontier-level performance across Enterprise and Consumer domains—with exceptional token efficiency. This model pushes the boundaries for smaller and faster AI, making high-quality reasoning accessible to more users and developers. Grok 4 Fast features state-of-the-art (SOTA) cost-efficiency, cutting-edge web and X search capabilities, a 2M token context window, and a unified architecture that blends reasoning and non-reasoning modes in one model.

Grok 4 Fast sets a new frontier in cost-efficient intelligence, outperforming Grok 3 Mini across reasoning benchmarks while slashing token costs.

We used large-scale reinforcement learning to maximize the intelligence density of Grok 4 Fast. In our evaluations, Grok 4 Fast achieves comparable performance to Grok 4 on benchmarks while using 40% fewer thinking tokens on average.

This 40% increase in Grok 4 Fast’s token efficiency, combined with a significantly lower price per token, results in a 98% reduction in price to achieve the same performance on frontier benchmarks as Grok 4. As verified by an independent review from Artificial Analysis, Grok 4 Fast exhibits a state-of-the-art (SOTA) price-to-intelligence ratio compared to other publicly available models on the Artificial Analysis Intelligence Index.

Grok 4 Fast was trained end-to-end with tool-use reinforcement learning (RL). It excels at deciding when to invoke tools like code execution or web browsing.

For instance, Grok 4 Fast exhibits frontier agentic search capabilities, seamlessly browsing the web and X to augment queries with real-time data. It hops through links, ingests media (including images and videos on X), and synthesizes findings at light speed.

Grok 4 Fast also establishes a new cost-effective frontier on general domain. We are excited to share Grok 4 Fast’s result on LMArena, where it has been privately battle-testing on the Search and Text Arenas.

In LMArena’s Search Arena, grok-4-fast-search (code name: menlo) claims #1 with 1163 Elo — a commanding margin of 17 over o3-search. Its superior reasoning efficiency and intelligence density enable it to surpass much larger models on real-world, search-related tasks.

In LMArena’s Text Arena, grok-4-fast (code name: tahoe) ranks #8, performing on par with grok-4-0709 and highlighting its remarkable intelligence density. Notably, it significantly outperforms peers in its weight class, where all comparable size models rank 18th or below.

Here are some examples of Grok 4 Fast in action:

Previously, separate reasoning modes required distinct models. Grok 4 Fast introduces a unified architecture where reasoning (long chain-of-thought) and non-reasoning (quick responses) are handled by the same model weights, steered via system prompts. This unification reduces end-to-end latency as well as token costs, making Grok 4 Fast ideal for real-time applications.

In grok.com, this results in smooth transitions: responding instantly for simple queries or engaging in extended reasoning for complex ones. In the xAI API, developers can fine-tune this behavior, optimizing for speed or depth.

Grok 4 Fast is available now for all users. In Fast and Auto modes, you will see a significant improvement in search and information seeking queries. Additionally, difficult queries in Auto mode will use Grok 4 Fast, which will provide a much faster experience without loss of quality. For the first time, all users, including free users, will have access to our latest model without restrictions, marking a step toward democratizing advanced AI.

For a limited time, Grok 4 Fast will be available for free on OpenRouter and Vercel AI Gateway.

We’re also rolling out Grok 4 Fast as two models: grok-4-fast-reasoning and grok-4-fast-non-reasoning, each with a 2M token context window. This allows developers to tune the amount of test-time compute applied to their use cases.

grok-4-fast-reasoning and grok-4-fast-non-reasoning are generally available via the xAI API according to the following pricing:

We will continuously ship model improvements to Grok 4 Fast based on your feedback on x.com. Stay tuned for further integrations, including enhanced multimodal capabilities and agentic features.

Read the Grok 4 Fast model card here.

That’s all for now – so long, and thanks for all the fish!

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