xAI: Grok 4 Fast✓ Catalog verified
Grok 4 Fast is xAI's latest multimodal model with SOTA cost-efficiency and a 2M token context window. It comes in two flavors: non-reasoning and reasoning. Read more about the model on xAI's news post. Reasoning can be enabled/disabled using the `reasoning` `enabled` parameter in the API. Learn more in our docs
Overview
Grok 4 Fast is xAI's latest multimodal model with SOTA cost-efficiency and a 2M token context window. It comes in two flavors: non-reasoning and reasoning. Read more about the model on xAI's news post. Reasoning can be enabled/disabled using the `reasoning` `enabled` parameter in the API. Learn more in our docs
Access: available through the official X Ai API. Context window: 2M.
Specifications
| API identifier | x-ai/grok-4-fast |
| Provider | X Ai |
| Model type | Multimodal LLM |
| Context window | 2M catalog |
| Input modalities | text · image |
| Output modalities | text |
| Released | Sep 19, 2025 |
| Tokenizer | Grok |
| Moderated | No |
| Architecture modality | text+image->text |
API defaults
{
"top_p": null,
"temperature": null,
"frequency_penalty": null
}Pricing
Live pricing components for x-ai/grok-4-fast as published in the catalog.
| Pricing component | Raw unit price | Normalized | Unit |
|---|---|---|---|
| Prompt tokens | $2e-7 | $0.20 / 1M | Per input token |
| Completion tokens | $5e-7 | $0.50 / 1M | Per output token |
| Request fee | N/A | N/A | Per request |
| Image fee | N/A | N/A | Per image unit |
| Web search fee | $0.005 | $0.005000 | Per search request |
Cost calculator
Estimate monthly spend from your own token volumes.
Estimated Total Cost
$0.2Calculated from current list pricing in the ModelsAtlas catalog.Capabilities
| Capability | Status | What it means |
|---|---|---|
| Visual Understanding | ✓ Supported | Image and document analysis support |
| Audio Processing | Not advertised | Speech and voice aligned flows |
| Tool Calling | ✓ Supported | Supports tools / function calling |
| Self-Hosting | Not advertised | Deploy outside managed APIs |
Capability signals
Directional signals derived from model metadata and capability tags — not official benchmark submissions.
Quick start
Call xAI: Grok 4 Fast through an OpenAI-compatible client.
from openai import OpenAI
client = OpenAI(
base_url="https://openrouter.ai/api/v1",
api_key="YOUR_API_KEY"
)
response = client.chat.completions.create(
model="x-ai/grok-4-fast",
messages=[{"role": "user", "content": "Explain quantum physics."}]
)
print(response.choices[0].message.content)Alternatives
Closest models by context window from a different provider.
| Model | Provider | Context | Input /1M | Actions |
|---|---|---|---|---|
| Auto Router | Openrouter | 2M | $-1000000.00 | View → |
| Auto Router (Beta) | Openrouter | 2M | $-1000000.00 | View → |
Head-to-head comparisons
Side-by-side breakdowns of xAI: Grok 4 Fast against other frontier models.
Sources & attribution
Pricing and metadata are maintained in the ModelsAtlas catalog.
Frequently asked questions
How much does xAI: Grok 4 Fast cost?
$0.20 per 1M input tokens and $0.50 per 1M output tokens on the official X Ai API.
What is the context window of xAI: Grok 4 Fast?
xAI: Grok 4 Fast supports up to 2M tokens of context.
Does xAI: Grok 4 Fast support tool / function calling?
Yes, xAI: Grok 4 Fast supports tool / function calling — you can register tools and the model will emit structured tool calls.
How do I access xAI: Grok 4 Fast?
Use the official X Ai API with the model id `x-ai/grok-4-fast`. See the Quick start section above for code examples.