The AI arena is free today

Open Superagent

GPT-5.1 Instant vs Grok-4.1 Fast Reasoning

Comparing GPT-5.1 Instant and Grok-4.1 Fast Reasoning across benchmarks, pricing, and capabilities.

OpenAI · xAI · Updated for 2026

Which is better?

GPT-5.1 Instant and Grok-4.1 Fast Reasoning trade strengths across price, capabilities, and technical limits. The better choice depends on the workload.

On price, Grok-4.1 Fast Reasoning is roughly 12.5x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Grok-4.1 Fast Reasoning also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.

Based on current benchmark, pricing, and model metadata for 2026.

Choose GPT-5.1 Instant

  • you want predictable pricing at $1.25/M input and $10.00/M output

Choose Grok-4.1 Fast Reasoning

  • cost matters — it's about 12.5x cheaper per token
  • you process long inputs — it offers a 2,000,000 token context window
  • you want the most recent training data — it shipped Nov 2025

At a glance

The differences that matter most.

GPT-5.1 Instant
OpenAI
Grok-4.1 Fast Reasoning
xAI
Benchmark wins
—
—
Input price
$1.25 / M
$0.20 / M
Output price
$10.00 / M
$0.50 / M
Context window
400,000
2,000,000
Released
Nov 2025
Nov 2025
License
Proprietary
Proprietary

Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

GPT-5.1 Instant and Grok-4.1 Fast Reasoningdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Arena Performance

Playground indexes and blind preference scores

Pricing Analysis

Price comparison per million tokens

Grok-4.1 Fast Reasoning costs less

For input processing, GPT-5.1 Instant ($1.25/1M tokens) is 6.3x more expensive than Grok-4.1 Fast Reasoning ($0.20/1M tokens).

For output processing, GPT-5.1 Instant ($10.00/1M tokens) is 20.0x more expensive than Grok-4.1 Fast Reasoning ($0.50/1M tokens).

In conclusion, GPT-5.1 Instant is more expensive than Grok-4.1 Fast Reasoning.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers
Tue Aug 25 2026 • llm-stats.com
OpenAI
GPT-5.1 Instant
Input tokens$1.25
Output tokens$10.00
Best providerOpenAI
xAI
Grok-4.1 Fast Reasoning
Input tokens$0.20
Output tokens$0.50
Best providerxAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Grok-4.1 Fast Reasoning accepts 2,000,000 input tokens compared to GPT-5.1 Instant's 400,000 tokens. GPT-5.1 Instant can generate longer responses up to 128,000 tokens, while Grok-4.1 Fast Reasoning is limited to 30,000 tokens.

OpenAI
GPT-5.1 Instant
Input400,000 tokens
Output128,000 tokens
xAI
Grok-4.1 Fast Reasoning
Input2,000,000 tokens
Output30,000 tokens
Tue Aug 25 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both GPT-5.1 Instant and Grok-4.1 Fast Reasoning support multimodal inputs.

They are both capable of processing various types of data, offering versatility in application.

GPT-5.1 Instant

Text
Images
Audio
Video

Grok-4.1 Fast Reasoning

Text
Images
Audio
Video

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

GPT-5.1 Instant

Proprietary

Closed source

Grok-4.1 Fast Reasoning

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.1 Instant was released on 2025-11-12, while Grok-4.1 Fast Reasoning was released on 2025-11-17.

Grok-4.1 Fast Reasoning is 0 month newer than GPT-5.1 Instant.

GPT-5.1 Instant

Nov 12, 2025

9 months ago

Grok-4.1 Fast Reasoning

Nov 17, 2025

9 months ago

5d newer

Knowledge Cutoff

When training data ends

Neither model specifies a knowledge cutoff date.

Unable to compare the recency of their training data.

No cutoff dates available

Provider Availability

GPT-5.1 Instant is available from OpenAI. Grok-4.1 Fast Reasoning is available from xAI.

GPT-5.1 Instant

openai logo
OpenAI
Input Price:Input: $1.25/1MOutput Price:Output: $10.00/1M

Grok-4.1 Fast Reasoning

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $0.50/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against GPT-5.1 Instant and Grok-4.1 Fast Reasoning side-by-side, then vote on the output you prefer.

GPT-5.1 Instant
✓ Preferred
Grok-4.1 Fast Reasoning
Open in Playground

FAQ

Common questions about GPT-5.1 Instant vs Grok-4.1 Fast Reasoning.

Which is better, GPT-5.1 Instant or Grok-4.1 Fast Reasoning?

GPT-5.1 Instant (OpenAI) and Grok-4.1 Fast Reasoning (xAI) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

How does GPT-5.1 Instant compare to Grok-4.1 Fast Reasoning in benchmarks?

GPT-5.1 Instant scores Tau2 Telecom: 95.6%, AIME 2025: 94.0%, BrowseComp Long Context 128k: 90.0%, GPQA: 88.1%, MMMU: 85.4%.

Is GPT-5.1 Instant cheaper than Grok-4.1 Fast Reasoning?

Grok-4.1 Fast Reasoning is 6.3x cheaper for input tokens. GPT-5.1 Instant costs $1.25/M input and $10.00/M output via openai. Grok-4.1 Fast Reasoning costs $0.20/M input and $0.50/M output via xai.

What are the context window sizes for GPT-5.1 Instant and Grok-4.1 Fast Reasoning?

GPT-5.1 Instant supports 400K tokens and Grok-4.1 Fast Reasoning supports 2.0M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-5.1 Instant and Grok-4.1 Fast Reasoning?

Key differences include context window (400K vs 2.0M), input pricing ($1.25 vs $0.20/M). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-5.1 Instant and Grok-4.1 Fast Reasoning?

GPT-5.1 Instant is developed by OpenAI and Grok-4.1 Fast Reasoning is developed by xAI.

Related comparisons