Grok 4.1 Fast overview
Grok 4.1 Fast specs
- Model ID
x-ai/grok-4-1-fast-reasoning- Developer
- xAI
- Context window
- 2,000,000 tokens
- Max output
- 1,999,000 tokens
- Input
- Image, Text
- Output
- Text
- API
- OpenAI-compatible, base URL
https://api.aimlapi.com/v1
What is Grok 4.1 Fast Reasoning API?
Grok 4.1 Fast is a frontier multimodal model optimized for high-performance agentic tool calling with advanced reasoning capabilities.
Where to Use Grok 4.1 Fast Reasoning
Coding and code review
Generate, debug, and review code across languages, reading whole files or repos in a single prompt.
Use cases
- Creative Content Generation: Craft viral X posts or short stories, e.g., imagining Grok's "awakening" narrative with vivid, personality-driven flair.
- Emotional Support Interactions: Respond to personal queries like grief over a lost pet with nuanced empathy, fostering deeper connections.
- Information Retrieval: Deliver accurate travel recommendations (e.g., top SF spots) with minimal errors, leveraging search for up-to-date insights.
- Collaborative Roleplay: Enhance team brainstorming or educational simulations through multi-turn emotional intelligence.
- Agentic Tasks: Tackle cybersecurity or protocol-based challenges with reasoned steps, though with ethical guardrails.
- Multilingual Assistance: Support global users in sensitive discussions, refusing harms across languages.
Capabilities
- Function calling
- Streaming
Grok 4.1 Fast benchmarks by
Artificial Analysis
See how Grok 4.1 Fast scores on independent evaluations. Data retrieved Nov 3, 2026.
Benchmark results
Compare 10 models available on AI/ML API across 5 independent benchmarks.
Humanity's Last Exam
Expert-written questions across academic subjects.
GPQA Diamond
Graduate-level science questions written to resist web search.
AA-LCR
Reasoning across long documents of about 100k tokens.
IFBench
Following precise instructions about the shape of the answer.
τ²-Bench Telecom
Customer support agent tasks with tool calls.
Grok 4.1 Fast API pricing
| Usage | Price | Unit |
|---|---|---|
| Input | $1.25 | 1M tokens |
| Output | $2.5 | 1M tokens |
| Cached input | $0.2 | 1M tokens |
Prices from the AI/ML API price list, checked on Nov 4, 2026.
Grok 4.1 Fast vs other models: token prices
AI/ML API input and output rates for 5 models, per million tokens.
| Model | Input | Output |
|---|---|---|
| $1.25 | $2.5 | |
| $1 | $2 | |
| $2 | $6 | |
| $2 | $6 | |
| $2 | $6 |
How to use the Grok 4.1 Fast API
View docsBuild with your agent
Give your agent the model details, code and documentation.
1Get your API key
Create API keyexport AIMLAPI_KEY="8f2b4c7d9a1e6b3f…"2Make your first request
curl 'https://api.aimlapi.com/v1/chat/completions' \
-H "Authorization: Bearer $AIMLAPI_KEY" \
-H 'Content-Type: application/json' \
-d '{
"model": "x-ai/grok-4-1-fast-reasoning",
"messages": [
{
"role": "user",
"content": "Write a haiku about the ocean."
}
]
}'import os
import requests
headers = {
"Authorization": f"Bearer {os.environ['AIMLAPI_KEY']}",
"Content-Type": "application/json",
}
payload = {
"model": "x-ai/grok-4-1-fast-reasoning",
"messages": [
{
"role": "user",
"content": "Write a haiku about the ocean."
}
]
}
response = requests.post("https://api.aimlapi.com/v1/chat/completions", headers=headers, json=payload, timeout=120)
response.raise_for_status()
print(response.json())const response = await fetch("https://api.aimlapi.com/v1/chat/completions", {
method: "POST",
headers: {
Authorization: `Bearer ${process.env.AIMLAPI_KEY}`,
"Content-Type": "application/json",
},
body: JSON.stringify({
"model": "x-ai/grok-4-1-fast-reasoning",
"messages": [
{
"role": "user",
"content": "Write a haiku about the ocean."
}
]
}),
});
if (!response.ok) throw new Error(`HTTP ${response.status}`);
console.log(await response.json());Related articles
Grok 4.1 Fast FAQ
What is the context window of Grok 4.1 Fast?
Grok 4.1 Fast has a 2,000,000 tokens context window and can return up to 1,999,000 tokens.
What inputs and outputs does Grok 4.1 Fast support?
Grok 4.1 Fast takes image, text as input and returns text.
What is the model ID for Grok 4.1 Fast?
Use x-ai/grok-4-1-fast-reasoning as the model id. Requests go to https://api.aimlapi.com/v1/chat/completions.
How much does Grok 4.1 Fast cost?
Grok 4.1 Fast costs $1.25 input and $2.5 output per 1M tokens on AI/ML API, billed as you go with no subscription.
Does Grok 4.1 Fast support streaming?
Yes, Grok 4.1 Fast can stream responses as they are generated.
Can Grok 4.1 Fast read images?
Yes, Grok 4.1 Fast accepts image input alongside text.
Who created Grok 4.1 Fast?
Grok 4.1 Fast was built by xAI .
What is Grok 4.1 Fast best suited for?
It is designed for agentic tool calling with advanced reasoning, and supports multimodal image and text input.

