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Model Comparison

Grok-4 Fast Reasoning vs Phi 4 Reasoning PlusWhich is better in 2026?

Comparing Grok-4 Fast Reasoning and Phi 4 Reasoning Plus across benchmarks, pricing, and capabilities.

Verdict: Grok-4 Fast Reasoning vs Phi 4 Reasoning Plus — which is better?

Grok-4 Fast Reasoning (by xAI) and Phi 4 Reasoning Plus (by Microsoft) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.

Choose Grok-4 Fast Reasoning if…

  • you want the most recent training data — it shipped Aug 2025

Choose Phi 4 Reasoning Plus if…

  • you need open weights you can self-host or fine-tune

Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

Grok-4 Fast Reasoning and Phi 4 Reasoning Plusdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Arena Performance

Human preference votes

Context Window

Maximum input and output token capacity

Only Grok-4 Fast Reasoning specifies input context (2,000,000 tokens). Only Grok-4 Fast Reasoning specifies output context (30,000 tokens).

xAI
Grok-4 Fast Reasoning
Input2,000,000 tokens
Output30,000 tokens
Microsoft
Phi 4 Reasoning Plus
Input- tokens
Output- tokens
Fri Aug 07 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Grok-4 Fast Reasoning supports multimodal inputs, whereas Phi 4 Reasoning Plus does not.

Grok-4 Fast Reasoning can handle both text and other forms of data like images, making it suitable for multimodal applications.

Grok-4 Fast Reasoning

Text
Images
Audio
Video

Phi 4 Reasoning Plus

Text
Images
Audio
Video

License

Usage and distribution terms

Grok-4 Fast Reasoning is licensed under a proprietary license, while Phi 4 Reasoning Plus uses MIT.

License differences may affect how you can use these models in commercial or open-source projects.

Grok-4 Fast Reasoning

Proprietary

Closed source

Phi 4 Reasoning Plus

MIT

Open weights

Release Timeline

When each model was launched

Grok-4 Fast Reasoning was released on 2025-08-28, while Phi 4 Reasoning Plus was released on 2025-04-30.

Grok-4 Fast Reasoning is 4 months newer than Phi 4 Reasoning Plus.

Grok-4 Fast Reasoning

Aug 28, 2025

11 months ago

4mo newer
Phi 4 Reasoning Plus

Apr 30, 2025

1.3 years ago

Knowledge Cutoff

When training data ends

Phi 4 Reasoning Plus has a documented knowledge cutoff of 2025-03-01, while Grok-4 Fast Reasoning's cutoff date is not specified.

We can confirm Phi 4 Reasoning Plus's training data extends to 2025-03-01, but cannot make a direct comparison without Grok-4 Fast Reasoning's cutoff date.

Grok-4 Fast Reasoning

—

Phi 4 Reasoning Plus

Mar 2025

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

xAI
Larger context window (2,000,000 tokens)
Supports multimodal inputs
Microsoft
Has open weights

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against Grok-4 Fast Reasoning and Phi 4 Reasoning Plus side-by-side, then vote on the output you prefer.

Grok-4 Fast Reasoning
✓ Preferred
Phi 4 Reasoning Plus
Open in Playground
AI Model Comparison Table
Feature
xAI
Grok-4 Fast Reasoning
Microsoft
Phi 4 Reasoning Plus

FAQ

Common questions about Grok-4 Fast Reasoning vs Phi 4 Reasoning Plus.

Which is better, Grok-4 Fast Reasoning or Phi 4 Reasoning Plus?

Grok-4 Fast Reasoning (xAI) and Phi 4 Reasoning Plus (Microsoft) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

How does Grok-4 Fast Reasoning compare to Phi 4 Reasoning Plus in benchmarks?

Phi 4 Reasoning Plus scores FlenQA: 97.9%, HumanEval+: 92.3%, IFEval: 84.9%, OmniMath: 81.9%, AIME 2024: 81.3%.

What are the context window sizes for Grok-4 Fast Reasoning and Phi 4 Reasoning Plus?

Grok-4 Fast Reasoning supports 2.0M tokens and Phi 4 Reasoning Plus supports an unknown number of tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between Grok-4 Fast Reasoning and Phi 4 Reasoning Plus?

Key differences include multimodal support (yes vs no), licensing (Proprietary vs MIT). See the full comparison above for benchmark-by-benchmark results.

Who makes Grok-4 Fast Reasoning and Phi 4 Reasoning Plus?

Grok-4 Fast Reasoning is developed by xAI and Phi 4 Reasoning Plus is developed by Microsoft.

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