Model Comparison
GPT-5.5 vs GLM-5.1Which is better in 2026?
GPT-5.5 significantly outperforms across most benchmarks. GLM-5.1 is 5.2x cheaper per token.
Verdict: GPT-5.5 vs GLM-5.1 — which is better?
GPT-5.5 (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 outperforms in 10 benchmarks (BrowseComp, CyberGym, Finance Agent v2, FrontierSWE, GPQA, LiveBench, MCP Atlas, SWE-Bench Pro, Terminal-Bench 2.0, Toolathlon), while GLM-5.1 is better at 2 benchmarks (GDPval-AA, Humanity's Last Exam). GPT-5.5 significantly outperforms across most benchmarks.
On price, GLM-5.1 is roughly 5.2x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
GPT-5.5 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 if…
- you want the strongest raw capability — it leads on 10 of 12 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 5.2x cheaper per token
- you need open weights you can self-host or fine-tune
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.5 outperforms in 10 benchmarks (BrowseComp, CyberGym, Finance Agent v2, FrontierSWE, GPQA, LiveBench, MCP Atlas, SWE-Bench Pro, Terminal-Bench 2.0, Toolathlon), while GLM-5.1 is better at 2 benchmarks (GDPval-AA, Humanity's Last Exam).
GPT-5.5 significantly outperforms across most benchmarks.
Arena Performance
Human preference votes
Pricing Analysis
Price comparison per million tokens
For input processing, GPT-5.5 ($5.00/1M tokens) is 3.6x more expensive than GLM-5.1 ($1.40/1M tokens).
For output processing, GPT-5.5 ($30.00/1M tokens) is 6.8x more expensive than GLM-5.1 ($4.40/1M tokens).
In conclusion, GPT-5.5 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 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 supports multimodal inputs, whereas GLM-5.1 does not.
GPT-5.5 can handle both text and other forms of data like images, making it suitable for multimodal applications.
GPT-5.5
GLM-5.1
License
Usage and distribution terms
GPT-5.5 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 was released on 2026-04-23, while GLM-5.1 was released on 2026-04-07.
GPT-5.5 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 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'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 is available from OpenAI. GLM-5.1 is available from FriendliAI, ZAI.
GPT-5.5
GLM-5.1
Outputs Comparison
Key Takeaways
GPT-5.5
View detailsOpenAI
GLM-5.1
View detailsZhipu AI
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.5 and GLM-5.1 side-by-side, then vote on the output you prefer.
FAQ
Common questions about GPT-5.5 vs GLM-5.1.