Model Comparison

GPT-5.1 Codex vs o1-previewWhich is better in 2026?

GPT-5.1 Codex significantly outperforms across most benchmarks. GPT-5.1 Codex is 7.6x cheaper per token.

Verdict: GPT-5.1 Codex vs o1-preview — which is better?

GPT-5.1 Codex (by OpenAI) and o1-preview (by OpenAI) 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.

GPT-5.1 Codex outperforms in 1 benchmarks (SWE-Bench Verified), while o1-preview is better at 0 benchmarks. GPT-5.1 Codex significantly outperforms across most benchmarks.

On price, GPT-5.1 Codex is roughly 7.6x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

GPT-5.1 Codex also accepts a larger context window (400,000 input tokens), making it the stronger choice for long documents and large codebases.

Choose GPT-5.1 Codex if…

  • you want the strongest raw capability — it leads on 1 of 1 shared benchmarks
  • cost matters — it's about 7.6x cheaper per token
  • you process long inputs — it offers a 400,000 token context window
  • you want the most recent training data — it shipped Nov 2025

Choose o1-preview if…

  • you want predictable pricing at $15.00/M input and $60.00/M output

Performance Benchmarks

Comparative analysis across standard metrics

1 benchmarks

GPT-5.1 Codex outperforms in 1 benchmarks (SWE-Bench Verified), while o1-preview is better at 0 benchmarks.

GPT-5.1 Codex significantly outperforms across most benchmarks.

Mon Jul 27 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

GPT-5.1 Codex costs less

For input processing, GPT-5.1 Codex ($1.25/1M tokens) is 12.0x cheaper than o1-preview ($15.00/1M tokens).

For output processing, GPT-5.1 Codex ($10.00/1M tokens) is 6.0x cheaper than o1-preview ($60.00/1M tokens).

In conclusion, o1-preview is more expensive than GPT-5.1 Codex.*

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

Lowest available price from all providers
Mon Jul 27 2026 • llm-stats.com
OpenAI
GPT-5.1 Codex
Input tokens$1.25
Output tokens$10.00
Best providerOpenAI
OpenAI
o1-preview
Input tokens$15.00
Output tokens$60.00
Best providerOpenAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

GPT-5.1 Codex accepts 400,000 input tokens compared to o1-preview's 128,000 tokens. GPT-5.1 Codex can generate longer responses up to 128,000 tokens, while o1-preview is limited to 32,768 tokens.

OpenAI
GPT-5.1 Codex
Input400,000 tokens
Output128,000 tokens
OpenAI
o1-preview
Input128,000 tokens
Output32,768 tokens
Mon Jul 27 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

GPT-5.1 Codex supports multimodal inputs, whereas o1-preview does not.

GPT-5.1 Codex can handle both text and other forms of data like images, making it suitable for multimodal applications.

GPT-5.1 Codex

Text
Images
Audio
Video

o1-preview

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 Codex

Proprietary

Closed source

o1-preview

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.1 Codex was released on 2025-11-19, while o1-preview was released on 2024-09-12.

GPT-5.1 Codex is 14 months newer than o1-preview.

GPT-5.1 Codex

Nov 19, 2025

8 months ago

1.2yr newer
o1-preview

Sep 12, 2024

1.9 years ago

Knowledge Cutoff

When training data ends

GPT-5.1 Codex has a documented knowledge cutoff of 2024-09-30, while o1-preview's cutoff date is not specified.

We can confirm GPT-5.1 Codex's training data extends to 2024-09-30, but cannot make a direct comparison without o1-preview's cutoff date.

GPT-5.1 Codex

Sep 2024

o1-preview

—

Provider Availability

GPT-5.1 Codex is available from OpenAI. o1-preview is available from OpenAI, Azure.

GPT-5.1 Codex

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

o1-preview

openai logo
OpenAI
Input Price:Input: $15.00/1MOutput Price:Output: $60.00/1M
azure logo
Azure
Input Price:Input: $16.50/1MOutput Price:Output: $66.00/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

OpenAI
Larger context window (400,000 tokens)
Supports multimodal inputs
Less expensive input tokens
Less expensive output tokens
Higher SWE-Bench Verified score (73.7% vs 41.3%)
OpenAI

No standout differentiators in the data we have for this pair.

Detailed Comparison

Interactive Arena

Judge for yourself.

Run your own prompts against GPT-5.1 Codex and o1-preview side-by-side, then vote on the output you prefer.

GPT-5.1 Codex
✓ Preferred
o1-preview
Open in Playground
AI Model Comparison Table
Feature
OpenAI
GPT-5.1 Codex
OpenAI
o1-preview

FAQ

Common questions about GPT-5.1 Codex vs o1-preview.

Which is better, GPT-5.1 Codex or o1-preview?

GPT-5.1 Codex significantly outperforms across most benchmarks. GPT-5.1 Codex is made by OpenAI and o1-preview is made by OpenAI. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.

How does GPT-5.1 Codex compare to o1-preview in benchmarks?

GPT-5.1 Codex scores SWE-Bench Verified: 73.7%, SWE-Lancer: 66.3%, Terminal-Bench 2.0: 52.8%. o1-preview scores MGSM: 90.8%, MMLU: 90.8%, MATH: 85.5%, GPQA: 73.3%, LiveBench: 52.3%.

Is GPT-5.1 Codex cheaper than o1-preview?

GPT-5.1 Codex is 12.0x cheaper for input tokens. GPT-5.1 Codex costs $1.25/M input and $10.00/M output via openai. o1-preview costs $15.00/M input and $60.00/M output via openai.

What are the context window sizes for GPT-5.1 Codex and o1-preview?

GPT-5.1 Codex supports 400K tokens and o1-preview supports 128K 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 Codex and o1-preview?

Key differences include context window (400K vs 128K), input pricing ($1.25 vs $15.00/M), multimodal support (yes vs no). See the full comparison above for benchmark-by-benchmark results.

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