Claude Sonnet 4.5 vs GPT-5.1 Codex Comparison

Comparing Claude Sonnet 4.5 and GPT-5.1 Codex across benchmarks, pricing, and capabilities.

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Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

Claude Sonnet 4.5 and GPT-5.1 Codex don't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

GPT-5.1 Codex costs less

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

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

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

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

Lowest available price from all providers

Tue Mar 17 2026 • llm-stats.com

Claude Sonnet 4.5

Input tokens$3.00

Output tokens$15.00

Best providerAnthropic

GPT-5.1 Codex

Input tokens$1.25

Output tokens$10.00

Best providerOpenAI

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Context Window

Maximum input and output token capacity

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

Claude Sonnet 4.5

Input200,000 tokens

Output64,000 tokens

GPT-5.1 Codex

Input400,000 tokens

Output128,000 tokens

Tue Mar 17 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both Claude Sonnet 4.5 and GPT-5.1 Codex 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 Codex

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 Codex

Proprietary

Closed source

Release Timeline

When each model was launched

Claude Sonnet 4.5 was released on 2025-09-29, while GPT-5.1 Codex was released on 2025-11-19.

GPT-5.1 Codex is 2 months newer than Claude Sonnet 4.5.

Claude Sonnet 4.5

Sep 29, 2025

5 months ago

GPT-5.1 Codex

Nov 19, 2025

3 months ago

1mo newer

Knowledge Cutoff

When training data ends

Claude Sonnet 4.5 has a knowledge cutoff of 2025-01-31, while GPT-5.1 Codex has a cutoff of 2024-09-30.

Claude Sonnet 4.5 has more recent training data (up to 2025-01-31), making it potentially better informed about events through that date compared to GPT-5.1 Codex (2024-09-30).

Claude Sonnet 4.5

Jan 2025

4 mo newer

GPT-5.1 Codex

Sep 2024

Provider Availability

Claude Sonnet 4.5 is available from Anthropic. GPT-5.1 Codex is available from OpenAI. The availability of providers can affect quality of the model and reliability.