Grok 4 Fast with reasoning enabled, using a unified architecture that blends reasoning and non-reasoning modes, with web and X search and a 2M token context window. xAI retired this slug on May 15, 2026; requests now route to Grok 4.3 with low reasoning effort.
Grok 4 Fast with reasoning enabled, using a unified architecture that blends reasoning and non-reasoning modes, with web and X search and a 2M token context window. xAI retired this slug on May 15, 2026; requests now route to Grok 4.3 with low reasoning effort.
Grok 4 Fast Reasoning is an AI model from xAI, available on ZeroTwo. It has a 2,000,000-token context window.
Intelligence
Fair
Speed
Medium
Input
Text
Output
Text
Grok 4 Fast with reasoning enabled, using a unified architecture that blends reasoning and non-reasoning modes, with web and X search and a 2M token context window. xAI retired this slug on May 15, 2026; requests now route to Grok 4.3 with low reasoning effort.
2,000,000 context window
Reasoning token support
Pricing
xAI retired the grok-4-fast-reasoning slug on May 15, 2026. Requests to it now route to grok-4.3 and are billed at grok-4.3 rates: $1.25 input and $2.50 output per million tokens below 200,000 prompt tokens, $2.50 and $5.00 at or above that threshold.
Modalities
Text
Input and output
Image
Not supported
Audio
Not supported
Endpoints
Chat Completions
v1/chat/completions
Responses
v1/responses
Batch
v1/batch
Realtime
v1/realtime
Assistants
v1/assistants
Fine-tuning
v1/fine-tuning
Embeddings
v1/embeddings
Image Generation
v1/images/generations
Image Edit
v1/images/edits
Speech Generation
v1/audio/speech
Transcription
v1/audio/transcriptions
Translation
v1/translations
Moderation
v1/moderations
Completions (legacy)
v1/completions
Features
Streaming
Supported
Function calling
Supported
Structured outputs
Not supported
Fine-tuning
Not supported
Distillation
Not supported
Fast response
Not supported
Cost efficient
Not supported
Tools
Tools supported by this model when using the Responses API.
Web search
Supported
Code interpreter
Not supported
File search
Not supported
Image generation
Not supported
MCP
Not supported
Snapshots
Snapshots let you lock in a specific version of the model so that performance and behavior remain consistent. Below is a list of all available snapshots and aliases for Grok 4 Fast Reasoning.
grok-4-fast-reasoning
Questions
What is Grok 4 Fast Reasoning's context window?
Grok 4 Fast Reasoning accepts up to 2,000,000 tokens of context.
Can I use Grok 4 Fast Reasoning for free?
You can try Grok 4 Fast Reasoning on ZeroTwo's free plan, which includes a monthly credit allowance across every model in the catalogue. Heavier use moves to a paid plan rather than a per-token bill.