Grok 4.1 Fast Reasoning overview
Grok 4.1 Fast Reasoning 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
Grok 4.1 Fast Reasoning is documented as suited to customer support, where it is described as handling complex real-world support tasks with fast, accurate agentic reasoning. It is also suited to finance, where the same source says it excels in complex real-world finance use cases.
It is suited to deep research and agentic search workflows, with documentation describing it as a production-grade agent model for tool calling and agentic search. It is also suited to rapid multi-step reasoning and structured decision-making, especially in analysis pipelines and other applications that need fast responses without losing reasoning depth.
Capabilities
- Function calling
- Streaming
Grok 4.1 Fast Reasoning benchmarks by
Artificial Analysis
See how Grok 4.1 Fast Reasoning 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 Reasoning 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 Reasoning 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 Reasoning 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());Grok 4.1 Fast Reasoning FAQ
What is the context window of Grok 4.1 Fast Reasoning?
Grok 4.1 Fast Reasoning 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 Reasoning support?
Grok 4.1 Fast Reasoning takes image, text as input and returns text.
What is the model ID for Grok 4.1 Fast Reasoning?
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 Reasoning cost?
Grok 4.1 Fast Reasoning 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 Reasoning support streaming?
Yes, Grok 4.1 Fast Reasoning can stream responses as they are generated.
Can Grok 4.1 Fast Reasoning read images?
Yes, Grok 4.1 Fast Reasoning accepts image input alongside text.
Who created Grok 4.1 Fast Reasoning?
Grok 4.1 Fast Reasoning was built by xAI .
Does Grok 4.1 Fast Reasoning support function calling?
Yes, it supports function calling as one of its core capabilities.