Grok 4.1 Fast 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 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 through AI/ML API

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.

Grok 4.1 Fast API pricing

Grok 4.1 Fast 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 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$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 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."
    }
  ]
}'

Related articles

All posts

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.

Start building with Grok 4.1 Fast

Grok 4.1 Fast 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."
    }
  ]
}'