Model Comparison

Claude Sonnet 4.5 vs GPT-5.1 Thinking

GPT-5.1 Thinking significantly outperforms across most benchmarks. GPT-5.1 Thinking is 1.7x cheaper per token.

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Performance Benchmarks

Comparative analysis across standard metrics

2 benchmarks

Claude Sonnet 4.5 outperforms in 0 benchmarks, while GPT-5.1 Thinking is better at 2 benchmarks (AIME 2025, GPQA).

GPT-5.1 Thinking significantly outperforms across most benchmarks.

Mon Apr 20 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

GPT-5.1 Thinking costs less

For input processing, Claude Sonnet 4.5 ($3.00/1M tokens) is 2.4x more expensive than GPT-5.1 Thinking ($1.25/1M tokens).

For output processing, Claude Sonnet 4.5 ($15.00/1M tokens) is 1.5x more expensive than GPT-5.1 Thinking ($10.00/1M tokens).

In conclusion, Claude Sonnet 4.5 is more expensive than GPT-5.1 Thinking.*

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

Lowest available price from all providers
Mon Apr 20 2026 • llm-stats.com
Anthropic
Claude Sonnet 4.5
Input tokens$3.00
Output tokens$15.00
Best providerAnthropic
OpenAI
GPT-5.1 Thinking
Input tokens$1.25
Output tokens$10.00
Best providerOpenAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

GPT-5.1 Thinking accepts 400,000 input tokens compared to Claude Sonnet 4.5's 200,000 tokens. GPT-5.1 Thinking can generate longer responses up to 128,000 tokens, while Claude Sonnet 4.5 is limited to 64,000 tokens.

Anthropic
Claude Sonnet 4.5
Input200,000 tokens
Output64,000 tokens
OpenAI
GPT-5.1 Thinking
Input400,000 tokens
Output128,000 tokens
Mon Apr 20 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Claude Sonnet 4.5 and GPT-5.1 Thinking support multimodal inputs.

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

Claude Sonnet 4.5

Text
Images
Audio
Video

GPT-5.1 Thinking

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 Sonnet 4.5

Proprietary

Closed source

GPT-5.1 Thinking

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Sonnet 4.5 was released on 2025-09-29, while GPT-5.1 Thinking was released on 2025-11-12.

GPT-5.1 Thinking is 1 month newer than Claude Sonnet 4.5.

Claude Sonnet 4.5

Sep 29, 2025

6 months ago

GPT-5.1 Thinking

Nov 12, 2025

5 months ago

1mo newer

Knowledge Cutoff

When training data ends

Claude Sonnet 4.5 has a documented knowledge cutoff of 2025-01-31, while GPT-5.1 Thinking's cutoff date is not specified.

We can confirm Claude Sonnet 4.5's training data extends to 2025-01-31, but cannot make a direct comparison without GPT-5.1 Thinking's cutoff date.

Claude Sonnet 4.5

Jan 2025

GPT-5.1 Thinking

—

Provider Availability

Claude Sonnet 4.5 is available from Anthropic. GPT-5.1 Thinking is available from OpenAI.

Claude Sonnet 4.5

anthropic logo
Anthropic
Input Price:Input: $3.00/1MOutput Price:Output: $15.00/1M

GPT-5.1 Thinking

openai logo
OpenAI
Input Price:Input: $1.25/1MOutput Price:Output: $10.00/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

Anthropic
OpenAI
Larger context window (400,000 tokens)
Less expensive input tokens
Less expensive output tokens
Higher AIME 2025 score (94.0% vs 87.0%)
Higher GPQA score (88.1% vs 83.4%)

Detailed Comparison

AI Model Comparison Table
Feature
Anthropic
Claude Sonnet 4.5
OpenAI
GPT-5.1 Thinking

FAQ

Common questions about Claude Sonnet 4.5 vs GPT-5.1 Thinking

GPT-5.1 Thinking significantly outperforms across most benchmarks. Claude Sonnet 4.5 is made by Anthropic and GPT-5.1 Thinking is made by OpenAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.
Claude Sonnet 4.5 scores MMMLU: 89.1%, AIME 2025: 87.0%, TAU-bench Retail: 86.2%, GPQA: 83.4%, MMMUval: 77.8%. GPT-5.1 Thinking scores Tau2 Telecom: 95.6%, AIME 2025: 94.0%, BrowseComp Long Context 128k: 90.0%, GPQA: 88.1%, MMMU: 85.4%.
GPT-5.1 Thinking is 2.4x cheaper for input tokens. Claude Sonnet 4.5 costs $3.00/M input and $15.00/M output via anthropic. GPT-5.1 Thinking costs $1.25/M input and $10.00/M output via openai.
Claude Sonnet 4.5 supports 200K tokens and GPT-5.1 Thinking supports 400K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.
Key differences include context window (200K vs 400K), input pricing ($3.00 vs $1.25/M). See the full comparison above for benchmark-by-benchmark results.
Claude Sonnet 4.5 is developed by Anthropic and GPT-5.1 Thinking is developed by OpenAI.