--- title: Grok 4 Fast link: https://x.ai/news/grok-4-fast source: x-ai published: 2025-09-19T00:00:00Z first_seen: 2026-10-19T01:26:53.998049939Z summary: Pushing the Frontier of Cost-Efficient Intelligence content: extracted html: 2025-09-19-grok-4-fast.html remote_preview: url: https://media.x.ai/v1/website/grok-4-fast-8c8d3e84.webp --- ![Abstract digital hummingbird](https://media.x.ai/cdn-cgi/image/fit=scale-down,onerror=redirect,width=6016,f=auto/v1/website/grok-4-fast-8c8d3e84.webp) 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. ## [Advancing Cost-Efficient Intelligence](https://x.ai/news/grok-4-fast#advancing-cost-efficient-intelligence) Grok 4 Fast sets a new frontier in cost-efficient intelligence, outperforming Grok 3 Mini across reasoning benchmarks while slashing token costs. | Benchmark pass@1 | Grok 4 Fast | Grok 4 | Grok 3 Mini (High) | GPT-5 (High) | GPT-5 Mini (High) | | ---------------- | ----------- | ------ | ------------------ | ------------ | ----------------- | | 85.7% | 87.5% | 79.0% | 85.7% | 82.3% | | | 92.0% | 91.7% | 83.0% | 94.6% | 91.1% | | | 93.3% | 90.0% | 74.0% | 93.3% | 87.8% | | | 20.0% | 25.4% | 11.0% | 24.8% | 16.7% | | | 80.0% | 79.0% | 70.0% | 86.8% | 77.4% | | 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. \*All Claude models were benchmarked with Extended Thinking. ## [Native Tool Use with SOTA Search](https://x.ai/news/grok-4-fast#native-tool-use-with-sota-search) 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. | Benchmark pass@1 | Grok 4 Fast | Grok 4 | Grok 3 (No Reasoning) | | ---------------- | ----------- | ------ | --------------------- | | 44.9% | 43.0% | — | | | 95.0% | 94.0% | 82.0% | | | 66.0% | 58.0% | 37.0% | | | 51.2% | 45.0% | 10.8% | | | 74.0% | 66.0% | 27.0% | | | 58.0% | 53.2% | 20.8% | | \*X Browse is an internal benchmark evaluating agent's multihop search and browsing capabilities on X. ## [Frontier of General Post-training](https://x.ai/news/grok-4-fast#frontier-of-general-post-training) 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](https://lmarena.ai/leaderboard/search), `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. ![Artificial Intelligence Search Arena](https://media.x.ai/cdn-cgi/image/fit=scale-down,onerror=redirect,width=6016,f=auto/v1/website/search_arena-c5105183.webp) In LMArena's [Text Arena](https://lmarena.ai/leaderboard/text), `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. ![Artificial Intelligence Text Arena](https://media.x.ai/cdn-cgi/image/fit=scale-down,onerror=redirect,width=6016,f=auto/v1/website/text_arena-fcc81749.webp) Here are some examples of Grok 4 Fast in action: What is the maximum number of experience points possible in Path of Exile 2? ## [Unified Model: Reasoning and Non-Reasoning](https://x.ai/news/grok-4-fast#unified-model-reasoning-and-non-reasoning) 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](http://grok.com/?q=What%20is%20the%20answer%20to%20life,%20the%20universe,%20and%20everything?&m=7), 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. ## [Grok 4 Fast on OpenRouter, Vercel AI Gateway, and the xAI API](https://x.ai/news/grok-4-fast#grok-4-fast-on-openrouter-vercel-ai-gateway-and-the-xai-api) We're 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](https://x.ai/api) according to the following pricing: | Token Type | <128k tokens | ≥128k tokens | | ------------------- | ------------ | ------------ | | Input tokens | $0.20 / 1M | $0.40 / 1M | | Output tokens | $0.50 / 1M | $1.00 / 1M | | Cached input tokens | $0.05 / 1M | | ## [What's Next](https://x.ai/news/grok-4-fast#whats-next) We will continuously ship model improvements to Grok 4 Fast based on your feedback on [x.com](http://x.com). Stay tuned for further integrations, including enhanced multimodal capabilities and agentic features. Read the Grok 4 Fast model card [here](https://data.x.ai/2025-09-19-grok-4-fast-model-card.pdf). That's all for now - so long, and thanks for all the fish!