GLM-4.5-Air vs GPT OSS 20B
GLM-4.5-Air (Z.ai) and GPT OSS 20B (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-4.5-Air | GPT OSS 20B | |
|---|---|---|
| Input price per 1M | $0.030 | $0.030 |
| Output price per 1M | $0.140 | $0.140 |
| Context window | 131K tokens | 131K tokens |
| Max output | 98K tokens | 33K tokens |
| Input types | text | text |
| Capabilities | tools, reasoning | JSON, reasoning |
| Author | Z.ai | OpenAI |
| LMArena Overall | 1384 | 1287 |
| LMArena Coding | 1397 | 1307 |
| LMArena Math | 1396 | 1317 |
| LMArena Creative writing | 1343 | 1201 |
| LMArena Instruction following | 1354 | 1236 |
| LMArena Hard prompts | 1379 | 1274 |
| GPQA Diamond | — | 60.8% |
| OTIS Mock AIME | — | 65.3% |
| Humanity's Last Exam | 8.1% | — |
Scores from LMArena and Epoch AI, as published; a blank cell means not measured there.
What a month costs on each
| Workload | GLM-4.5-Air | GPT OSS 20B |
|---|---|---|
| Chatbot month (15M in, 4M out) | $1.01 | $1.01 |
| RAG month (40M in, 3M out) | $1.62 | $1.62 |
| Coding month (60M in, 10M out) | $3.20 | $3.20 |
On a typical 75/25 input-output mix, GLM-4.5-Air costs less. GLM-4.5-Air takes the longer prompt at 131K 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-4.5-air", "messages": [{"role": "user", "content": "Hello"}]}'
# the other one: change the model string
-d '{"model": "openai/gpt-oss-20b:free", ...}'Common questions
Which is cheaper, GLM-4.5-Air or GPT OSS 20B?
GLM-4.5-Air is cheaper on a typical mix of 75% input and 25% output tokens. Through Rapid Router both are billed at the provider list price per million tokens.
Which has the larger context window?
GLM-4.5-Air, at 131K tokens. GPT OSS 20B offers 131K tokens.
Can I switch between GLM-4.5-Air and GPT OSS 20B 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-4.5-air or openai/gpt-oss-20b:free).
How do I pay for GLM-4.5-Air or GPT OSS 20B?
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