Model Comparison
GPT-5.5 Pro vs GLM-5.1Which is better in 2026?
GPT-5.5 Pro significantly outperforms across most benchmarks. GLM-5.1 is 31.4x cheaper per token.
Verdict: GPT-5.5 Pro vs GLM-5.1 — which is better?
GPT-5.5 Pro (by OpenAI) and GLM-5.1 (by Zhipu AI) 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-5.5 Pro outperforms in 2 benchmarks (BrowseComp, Humanity's Last Exam), while GLM-5.1 is better at 0 benchmarks. GPT-5.5 Pro significantly outperforms across most benchmarks.
On price, GLM-5.1 is roughly 31.4x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
GPT-5.5 Pro also accepts a larger context window (1,050,000 input tokens), making it the stronger choice for long documents and large codebases.
Choose GPT-5.5 Pro if…
- you want the strongest raw capability — it leads on 2 of 2 shared benchmarks
- you process long inputs — it offers a 1,050,000 token context window
- you want the most recent training data — it shipped Apr 2026
Choose GLM-5.1 if…
- cost matters — it's about 31.4x cheaper per token
- you need open weights you can self-host or fine-tune
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.5 Pro outperforms in 2 benchmarks (BrowseComp, Humanity's Last Exam), while GLM-5.1 is better at 0 benchmarks.
GPT-5.5 Pro significantly outperforms across most benchmarks.
Arena Performance
Human preference votes
Pricing Analysis
Price comparison per million tokens
For input processing, GPT-5.5 Pro ($30.00/1M tokens) is 21.4x more expensive than GLM-5.1 ($1.40/1M tokens).
For output processing, GPT-5.5 Pro ($180.00/1M tokens) is 40.9x more expensive than GLM-5.1 ($4.40/1M tokens).
In conclusion, GPT-5.5 Pro is more expensive than GLM-5.1.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
GPT-5.5 Pro accepts 1,050,000 input tokens compared to GLM-5.1's 200,000 tokens. Both models can generate responses up to 128,000 tokens.
Input Capabilities
Supported data types and modalities
GPT-5.5 Pro supports multimodal inputs, whereas GLM-5.1 does not.
GPT-5.5 Pro can handle both text and other forms of data like images, making it suitable for multimodal applications.
GPT-5.5 Pro
GLM-5.1
License
Usage and distribution terms
GPT-5.5 Pro is licensed under a proprietary license, while GLM-5.1 uses MIT.
License differences may affect how you can use these models in commercial or open-source projects.
Proprietary
Closed source
MIT
Open weights
Release Timeline
When each model was launched
GPT-5.5 Pro was released on 2026-04-23, while GLM-5.1 was released on 2026-04-07.
GPT-5.5 Pro is 1 month newer than GLM-5.1.
Apr 23, 2026
2 months ago
2w newerApr 7, 2026
3 months ago
Knowledge Cutoff
When training data ends
GPT-5.5 Pro has a documented knowledge cutoff of 2025-12-01, while GLM-5.1's cutoff date is not specified.
We can confirm GPT-5.5 Pro's training data extends to 2025-12-01, but cannot make a direct comparison without GLM-5.1's cutoff date.
Dec 2025
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Provider Availability
GPT-5.5 Pro is available from OpenAI. GLM-5.1 is available from FriendliAI, ZAI.
GPT-5.5 Pro
GLM-5.1
Outputs Comparison
Key Takeaways
GPT-5.5 Pro
View detailsOpenAI
GLM-5.1
View detailsZhipu AI
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.5 Pro and GLM-5.1 side-by-side, then vote on the output you prefer.
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FAQ
Common questions about GPT-5.5 Pro vs GLM-5.1.