SyncDev model directory · Profile updated Oct 13, 2026
X-Ai/Grok-4-Fast-Reasoning from xAI: Fast Grok model for responsive chat, reasoning, and tool-assisted work.
Recorded modality support shows what this model can accept and produce. An undocumented modality is shown as unknown rather than assumed to be unsupported.
Accepts
Produces
Fast Grok model for responsive chat, reasoning, and tool-assisted work. The registry places it in the xAI catalog with a release date of 2025-12-18. This profile describes its documented interface and how to evaluate it for the intended task.
The recorded inputs are text, image, audio and video, with text output. The registry lists a 2,000,000-token context window and up to 2,000,000 output tokens. It also declares reasoning and function calling. These are specifications, not a measured quality or speed ranking. A host can impose its own request limits and support a different subset of features.
X-Ai/Grok-4-Fast-Reasoning is recorded as a hosted model without downloadable weights. Confirm the current model ID and access conditions on the chosen API. A registry listing alone does not establish that an account or region has access.
No independently checked token rate is added from a hosting alias. Use the route’s current price and billing unit when comparing cost, including output, reasoning, cache behavior and retries where applicable.
Test photographs, screenshots and documents with the detail your application needs to read. Include small text, crowded layouts and questions whose answer is absent. Check whether the answer is supported by the image instead of accepting a plausible description.
This is a registry-sourced profile. A model-specific publisher document has not yet been confirmed; access and specifications should be checked before an integration decision. SyncDev has not independently benchmarked X-Ai/Grok-4-Fast-Reasoning.
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Compare the model on the work you need to complete.
X-Ai/Grok-4-Fast-Reasoning is listed for Audio-text-to-text, Image-text-to-text, Text generation, Video-text-to-text. It accepts text, image, audio, video and produces text. Use the publisher’s input format and preprocessing for your chosen deployment.
Documented limits: 2M context and 2M maximum output. Measure a completed task using the prompts, documents and tools your application will use. Include reasoning and retries in the result.
Use the model identifier and account requirements for the selected API route. Confirm its request limits and output format with one complete task before connecting a larger workflow.
These records share a directory category. Check the source card, output type and deployment requirements before treating a model as a replacement.
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