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GPT-5.1 Thinking vs Kimi K2.8 Preview

Comparing GPT-5.1 Thinking and Kimi K2.8 Preview across benchmarks, pricing, and capabilities.

OpenAI · Moonshot AI · Updated for 2026

Which is better?

GPT-5.1 Thinking and Kimi K2.8 Preview trade strengths across price, capabilities, and technical limits. The better choice depends on the workload.

Kimi K2.8 Preview also accepts a larger context window (1,048,576 input tokens), making it the stronger choice for long documents and large codebases.

Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.

Choose GPT-5.1 Thinking

  • you want predictable pricing at $1.25/M input and $10.00/M output

Choose Kimi K2.8 Preview

  • you process long inputs — it offers a 1,048,576 token context window
  • you want the most recent training data — it shipped Sep 2026

At a glance

The differences that matter most.

GPT-5.1 Thinking
OpenAI
Kimi K2.8 Preview
Moonshot AI
Benchmark wins
—
—
Input price
$1.25 / M
— / M
Output price
$10.00 / M
— / M
Context window
400,000
1,048,576

Individual benchmarks

9 reported for GPT-5.1 Thinking · 0 for Kimi K2.8 Preview

No common benchmarks found

GPT-5.1 Thinking and Kimi K2.8 Previewdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Human preference

Blind head-to-head votes and playground preference scores

Context Window

Maximum input and output token capacity

Kimi K2.8 Preview accepts 1,048,576 input tokens compared to GPT-5.1 Thinking's 400,000 tokens. Only GPT-5.1 Thinking specifies output context (128,000 tokens).

OpenAI
GPT-5.1 Thinking
Input400,000 tokens
Output128,000 tokens
Moonshot AI
Kimi K2.8 Preview
Input1,048,576 tokens
Output- tokens
Sun Sep 20 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both GPT-5.1 Thinking and Kimi K2.8 Preview support multimodal inputs.

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

GPT-5.1 Thinking

Text
Images
Audio
Video

Kimi K2.8 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 Thinking

Proprietary

Closed source

Kimi K2.8 Preview

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5.1 Thinking was released on 2025-11-12, while Kimi K2.8 Preview was released on 2026-09-11.

Kimi K2.8 Preview is 10 months newer than GPT-5.1 Thinking.

GPT-5.1 Thinking

Nov 12, 2025

10 months ago

Kimi K2.8 Preview

Sep 11, 2026

1 weeks ago

10mo newer

Knowledge Cutoff

When training data ends

Neither model specifies a knowledge cutoff date.

Unable to compare the recency of their training data.

No cutoff dates available

Provider Availability

GPT-5.1 Thinking is available from OpenAI. Kimi K2.8 Preview is available from Moonshot AI.

GPT-5.1 Thinking

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

Kimi K2.8 Preview

moonshot logo
Unknown Organization
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against GPT-5.1 Thinking and Kimi K2.8 Preview side-by-side, then vote on the output you prefer.

GPT-5.1 Thinking
✓ Preferred
Kimi K2.8 Preview
Open in Playground

FAQ

Common questions about GPT-5.1 Thinking vs Kimi K2.8 Preview.

Which is better, GPT-5.1 Thinking or Kimi K2.8 Preview?

GPT-5.1 Thinking (OpenAI) and Kimi K2.8 Preview (Moonshot AI) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

How does GPT-5.1 Thinking compare to Kimi K2.8 Preview in benchmarks?

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%.

What are the context window sizes for GPT-5.1 Thinking and Kimi K2.8 Preview?

GPT-5.1 Thinking supports 400K tokens and Kimi K2.8 Preview supports 1.0M 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 Thinking and Kimi K2.8 Preview?

Key differences include context window (400K vs 1.0M). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-5.1 Thinking and Kimi K2.8 Preview?

GPT-5.1 Thinking is developed by OpenAI and Kimi K2.8 Preview is developed by Moonshot AI.

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