Model Comparison

Claude Opus 4.5 vs Grok 4 FastWhich is better in 2026?

Claude Opus 4.5 significantly outperforms across most benchmarks. Grok 4 Fast is 36.4x cheaper per token.

Verdict: Claude Opus 4.5 vs Grok 4 Fast — which is better?

Claude Opus 4.5 (by Anthropic) and Grok 4 Fast (by xAI) 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.

Claude Opus 4.5 outperforms in 1 benchmarks (GPQA), while Grok 4 Fast is better at 0 benchmarks. Claude Opus 4.5 significantly outperforms across most benchmarks.

On price, Grok 4 Fast is roughly 36.4x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Grok 4 Fast also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.

Choose Claude Opus 4.5 if…

  • you want the strongest raw capability — it leads on 1 of 1 shared benchmarks
  • you want the most recent training data — it shipped Nov 2025

Choose Grok 4 Fast if…

  • cost matters — it's about 36.4x cheaper per token
  • you process long inputs — it offers a 2,000,000 token context window
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Performance Benchmarks

Comparative analysis across standard metrics

1 benchmarks

Claude Opus 4.5 outperforms in 1 benchmarks (GPQA), while Grok 4 Fast is better at 0 benchmarks.

Claude Opus 4.5 significantly outperforms across most benchmarks.

Mon Jun 08 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Grok 4 Fast costs less

For input processing, Claude Opus 4.5 ($5.00/1M tokens) is 25.0x more expensive than Grok 4 Fast ($0.20/1M tokens).

For output processing, Claude Opus 4.5 ($25.00/1M tokens) is 50.0x more expensive than Grok 4 Fast ($0.50/1M tokens).

In conclusion, Claude Opus 4.5 is more expensive than Grok 4 Fast.*

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

Lowest available price from all providers
Mon Jun 08 2026 • llm-stats.com
Anthropic
Claude Opus 4.5
Input tokens$5.00
Output tokens$25.00
Best providerAnthropic
xAI
Grok 4 Fast
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 Fast accepts 2,000,000 input tokens compared to Claude Opus 4.5's 200,000 tokens. Claude Opus 4.5 can generate longer responses up to 64,000 tokens, while Grok 4 Fast is limited to 30,000 tokens.

Anthropic
Claude Opus 4.5
Input200,000 tokens
Output64,000 tokens
xAI
Grok 4 Fast
Input2,000,000 tokens
Output30,000 tokens
Mon Jun 08 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Claude Opus 4.5 and Grok 4 Fast support multimodal inputs.

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

Claude Opus 4.5

Text
Images
Audio
Video

Grok 4 Fast

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.

Claude Opus 4.5

Proprietary

Closed source

Grok 4 Fast

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Opus 4.5 was released on 2025-11-24, while Grok 4 Fast was released on 2025-08-28.

Claude Opus 4.5 is 3 months newer than Grok 4 Fast.

Claude Opus 4.5

Nov 24, 2025

6 months ago

2mo newer
Grok 4 Fast

Aug 28, 2025

9 months ago

Knowledge Cutoff

When training data ends

Claude Opus 4.5 has a documented knowledge cutoff of 2025-03-31, while Grok 4 Fast's cutoff date is not specified.

We can confirm Claude Opus 4.5's training data extends to 2025-03-31, but cannot make a direct comparison without Grok 4 Fast's cutoff date.

Claude Opus 4.5

Mar 2025

Grok 4 Fast

—

Provider Availability

Claude Opus 4.5 is available from Anthropic. Grok 4 Fast is available from xAI.

Claude Opus 4.5

anthropic logo
Anthropic
Input Price:Input: $5.00/1MOutput Price:Output: $25.00/1M

Grok 4 Fast

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→

Key Takeaways

Anthropic
Higher GPQA score (87.0% vs 85.7%)
xAI
Larger context window (2,000,000 tokens)
Less expensive input tokens
Less expensive output tokens

Detailed Comparison

AI Model Comparison Table
Feature
Anthropic
Claude Opus 4.5
xAI
Grok 4 Fast

FAQ

Common questions about Claude Opus 4.5 vs Grok 4 Fast.

Which is better, Claude Opus 4.5 or Grok 4 Fast?

Claude Opus 4.5 significantly outperforms across most benchmarks. Claude Opus 4.5 is made by Anthropic and Grok 4 Fast is made by xAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does Claude Opus 4.5 compare to Grok 4 Fast in benchmarks?

Claude Opus 4.5 scores Tau2 Telecom: 98.2%, MMMLU: 90.8%, Tau2 Retail: 88.9%, GPQA: 87.0%, SWE-Bench Verified: 80.9%. Grok 4 Fast scores SimpleQA: 95.0%, HMMT 2025: 93.3%, AIME 2025: 92.0%, GPQA: 85.7%, LiveCodeBench: 80.0%.

Is Claude Opus 4.5 cheaper than Grok 4 Fast?

Grok 4 Fast is 25.0x cheaper for input tokens. Claude Opus 4.5 costs $5.00/M input and $25.00/M output via anthropic. Grok 4 Fast costs $0.20/M input and $0.50/M output via xai.

What are the context window sizes for Claude Opus 4.5 and Grok 4 Fast?

Claude Opus 4.5 supports 200K tokens and Grok 4 Fast 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 Claude Opus 4.5 and Grok 4 Fast?

Key differences include context window (200K vs 2.0M), input pricing ($5.00 vs $0.20/M). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Opus 4.5 and Grok 4 Fast?

Claude Opus 4.5 is developed by Anthropic and Grok 4 Fast is developed by xAI.

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