Model comparison
GLM-5.3 vs GPT 5.5
GLM-5.3 (Z.ai) and GPT 5.5 (OpenAI) side by side: what each costs per million tokens through Rapid Router, how much context each takes, what each supports, and where independent benchmarks place them. Same API, same key; switching is a one-string change.
| GLM-5.3 | GPT 5.5 | |
|---|---|---|
| Input price per 1M | $0.079 | $5.00 |
| Output price per 1M | $4.80 | $30.00 |
| Context window | 1M tokens | 1.1M tokens |
| Max output | 131K tokens | 128K tokens |
| Input types | text | text, image, pdf |
| Capabilities | tools, JSON, reasoning | tools, JSON, vision, reasoning |
| Author | Z.ai | OpenAI |
| LMArena Overall | 1472 | 1471 |
| LMArena Coding | 1495 | 1494 |
| LMArena Math | 1491 | 1487 |
| LMArena Creative writing | 1456 | 1455 |
| LMArena Instruction following | 1476 | 1479 |
| LMArena Hard prompts | 1488 | 1489 |
| LMArena Vision | — | 1297 |
| LMArena Web dev | 1621 | — |
| GPQA Diamond | 90.9% | 90.7% |
| OTIS Mock AIME | 91.1% | 84.4% |
| SimpleQA Verified | 41.0% | 63.0% |
Scores from LMArena and Epoch AI, as published; a blank cell means not measured there.
What a month costs on each
| Workload | GLM-5.3 | GPT 5.5 |
|---|---|---|
| Chatbot month (15M in, 4M out) | $20.38 | $195.00 |
| RAG month (40M in, 3M out) | $17.56 | $290.00 |
| Coding month (60M in, 10M out) | $52.74 | $600.00 |
On a typical 75/25 input-output mix, GLM-5.3 costs less (about 89% less than GPT 5.5). GPT 5.5 takes the longer prompt at 1.1M tokens. Try your own numbers in the cost calculator.
Call either one
curl https://rapidrouter.ai/api/v1/chat/completions \
-H "Authorization: Bearer $RAPIDROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model": "z-ai/glm-5.3", "messages": [{"role": "user", "content": "Hello"}]}'
# the other one: change the model string
-d '{"model": "openai/gpt-5.5", ...}'Common questions
Which is cheaper, GLM-5.3 or GPT 5.5?
GLM-5.3 is cheaper on a typical mix of 75% input and 25% output tokens, by about 89%. Through Rapid Router both are billed at the provider list price per million tokens.
Which has the larger context window?
GPT 5.5, at 1.1M tokens. GLM-5.3 offers 1M tokens.
Can I switch between GLM-5.3 and GPT 5.5 without changing code?
Yes. Both are callable at https://rapidrouter.ai/api/v1 with the same OpenAI-compatible request; only the model string changes (z-ai/glm-5.3 or openai/gpt-5.5).
How do I pay for GLM-5.3 or GPT 5.5?
Top up a Rapid Router balance by card in US dollars, and both models debit that balance per request.
More GLM models: Z.ai API pricing · More GPT: OpenAI API pricing