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.

Modalities
Image, TextText
In / Out price
$1.25/$2.5per 1M
Context window
2M tokens
Released
Nov 20, 2025

Grok 4.1 Fast Reasoning overview

The pelican test: one prompt, every text model, unedited SVG output from Nov 3, 2026.

SVG of a pelican riding a bicycle, written by Grok 4.1 Fast Reasoning through AI/ML API

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.

Grok 4.1 Fast Reasoning API pricing

Grok 4.1 Fast Reasoning pricing in US dollars
UsagePriceUnit
Input$1.251M tokens
Output$2.51M tokens
Cached input$0.21M 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.

AI/ML API model prices in USD per million tokens
ModelInputOutput
Grok 4.1 Fast Reasoning$1.25$2.5
Grok Build 0.1$1$2
Grok 4.7$2$6
Grok 4.6$2$6
Grok 4.5$2$6

How to use the Grok 4.1 Fast Reasoning API

View docs

Build with your agent

Give your agent the model details, code and documentation.

1Get your API key

Create API key
export 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."
    }
  ]
}'

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.

Start building with Grok 4.1 Fast Reasoning

Grok 4.1 Fast Reasoning API

x-ai/grok-4-1-fast-reasoning

Build with your agent

Give your agent the model details, code and documentation.

1Get your API key

Create API key
export 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."
    }
  ]
}'