GLM-5.1 vs GPT-5.5
GLM-5.1 and GPT-5.5 are both current production-tier models. GLM-5.1 is meaningfully cheaper at $1 / $3.2 per 1M. GPT-5.5 has a 1.1M context window — about 5× the 200k of GLM-5.1. GPT-5.5 leads on reasoning, general knowledge, long-context retrieval.
Specs side by side
| Metric | Z.ai GLM-5.1 | OpenAI GPT-5.5 |
|---|---|---|
| Input price (per 1M) | $1 | $5 |
| Output price (per 1M) | $3.2 | $30 |
| Context window | 200k tokens | 1.1M tokens |
| Speed tier | balanced | balanced |
| Open weights | Yes | No |
| EU region | No | Yes |
| Free tier | bigmodel.cn | No |
| Prompt caching | No | Yes |
| Vision input | No | Yes |
| Extended thinking | Yes | Yes |
When to choose each
Choose GLM-5.1 if…
- Cost is a priority ($1 / $3.2 per 1M vs $5 / $30 per 1M)
- You need open weights for self-hosting or fine-tuning
- You want a free tier for prototyping
Choose GPT-5.5 if…
- You need 1.1M context (5× more than GLM-5.1)
- EU data residency is required
- HIPAA eligibility is required
- You need image input / vision
- You need realtime speech-to-speech
- Reasoning is central to your workload
- General knowledge is central to your workload
Benchmark delta
GLM-5.1 leads on
GLM-5.1 has no meaningful benchmark lead in this pair.
GPT-5.5 leads on
- Reasoning
- General knowledge
- Long-context retrieval
- Instruction following
- Tool use
FAQ — GLM-5.1 vs GPT-5.5
GLM-5.1 vs GPT-5.5 — which is better?
GLM-5.1 and GPT-5.5 are both current production-tier models. GLM-5.1 is meaningfully cheaper at $1 / $3.2 per 1M. GPT-5.5 has a 1.1M context window — about 5× the 200k of GLM-5.1. GPT-5.5 leads on reasoning, general knowledge, long-context retrieval. The right pick depends on your use case — see "When to choose each" above for a data-driven decision.
How does GLM-5.1 pricing compare to GPT-5.5?
GLM-5.1 costs $1 / $3.2 per 1M vs GPT-5.5 at $5 / $30 per 1M. GLM-5.1 is cheaper on output tokens by roughly 838%. Both support prompt caching, which reduces effective cost by 80-90% on repeat system prompts.
Does GLM-5.1 or GPT-5.5 have the bigger context window?
GPT-5.5 has a 1.1M-token context window — 5× the 200k context of GLM-5.1. Enough for entire codebases, books, or multi-document RAG.
Is there a free tier for GLM-5.1 or GPT-5.5?
GLM-5.1: yes — Free tier with monthly token allowance. GPT-5.5: no — Paid-only — no free API tier; available via ChatGPT Plus/Pro.
Which is better for coding — GLM-5.1 or GPT-5.5?
GPT-5.5 leads on coding benchmarks (GLM-5.1: 93/100, GPT-5.5: 95/100). For production coding agents also weigh tool-use performance — GLM-5.1 scores 86, GPT-5.5 scores 94.