Grok 4 Fast arrives as a clear bet: bring top-tier reasoning to more people, and make it cheaper and faster. Does that sound like the usual industry promise? Let me show you why this time it makes sense and what you can try today.

What is Grok 4 Fast

Grok 4 Fast is the new version of xAI's Grok models, designed to be more token-efficient and cheaper when running complex reasoning. It was announced on September 19, 2025 and, according to xAI, keeps frontier-level performance while cutting the cost per reasoning. (x.ai)

Performance and efficiency

More intelligence for fewer tokens? That's the bet. xAI claims Grok 4 Fast uses on average 40% fewer "thinking tokens" than Grok 4, which translates to up to a 98% reduction in the price needed to reach the same performance on certain benchmarks. In practice, that means long, step-by-step tasks become much cheaper. (x.ai)

Examples of benchmarks

In public evaluations, Grok 4 Fast posts competitive results on tests like GPQA, AIME and HMMT, and in public arenas like LMArena it ranks well on search and text tasks. Those numbers suggest that efficiency doesn't always come at the cost of quality. (x.ai)

Native search and tool use

A notable feature is that Grok 4 Fast was trained with integrated tool training. That lets it decide when to run code, browse the web, or use X to fetch real-time data, link sources and summarize findings. In xAI's public demo the model browses pages and synthesizes complex answers from multiple sources. If you work with online research or assistants that need up-to-date data, this matters. (x.ai)

Grok 4 Fast can 'jump' between links, read images and videos on X and return quick syntheses without losing context. (x.ai)

Unified architecture: reasoning and quick replies

Before, some solutions separated long-form reasoning and short replies into different weights. Grok 4 Fast unifies both modes in the same model and uses system prompts to steer its behavior. What do you gain from that? Lower latency and fewer tokens wasted when switching between simple and complex tasks. It also offers a huge context window: 2 million tokens, which opens scenarios like analyzing long documents or extended chat sessions. (x.ai)

Availability and pricing

Grok 4 Fast is available at grok.com and in the iOS and Android apps; xAI says that for the first time all users, including free accounts, will have access to the model in Fast and Auto modes depending on load and query complexity. For developers there are two API variants: grok-4-fast-reasoning and grok-4-fast-non-reasoning, both with the 2M token window. xAI also published the token pricing table for input and output. (x.ai)

If you want to see the official note and the technical sheet, you can visit Grok on their site and the model card they published. (x.ai)

And what does this mean for you?

If you're an entrepreneur or developer: this lowers the cost barrier to integrate advanced reasoning into real-time apps. If you use AI for search or agents that navigate the web, Grok 4 Fast promises faster, cheaper answers.

If you're a general user: you'll notice it in the speed and quality of searches when you use Grok in Fast or Auto mode. xAI says even free accounts will see the improvement, so it's worth trying. (x.ai)

Final thoughts

Grok 4 Fast isn't just a speed update. It's a push to make advanced reasoning practical and affordable for more real-world cases. Does it mean it replaces every large model? Not necessarily. But it does shift the conversation: token efficiency and native tool integration are becoming as important as raw brute force.

If you want, I can summarize the technical model card or prepare a quick comparison with other models you're interested in.