Model comparison
GPT 5.5 vs Grok 4.5
GPT 5.5 (OpenAI) and Grok 4.5 (xAI) 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.
| GPT 5.5 | Grok 4.5 | |
|---|---|---|
| Input price per 1M | $5.00 | $2.00 |
| Output price per 1M | $30.00 | $6.00 |
| Context window | 1.1M tokens | 500K tokens |
| Max output | 128K tokens | 500K tokens |
| Input types | text, image, pdf | text, image, pdf |
| Capabilities | tools, JSON, vision, reasoning | tools, JSON, vision, reasoning |
| Author | OpenAI | xAI |
| LMArena Overall | 1471 | 1448 |
| LMArena Coding | 1494 | 1474 |
| LMArena Math | 1487 | 1459 |
| LMArena Creative writing | 1455 | 1442 |
| LMArena Instruction following | 1479 | 1446 |
| LMArena Hard prompts | 1489 | 1462 |
| LMArena Vision | 1297 | 1288 |
| LMArena Web dev | — | 1553 |
| GPQA Diamond | 90.7% | 93.4% |
| OTIS Mock AIME | 84.4% | 97.8% |
| SimpleQA Verified | 63.0% | 48.3% |
Scores from LMArena and Epoch AI, as published; a blank cell means not measured there.
What a month costs on each
| Workload | GPT 5.5 | Grok 4.5 |
|---|---|---|
| Chatbot month (15M in, 4M out) | $195.00 | $54.00 |
| RAG month (40M in, 3M out) | $290.00 | $98.00 |
| Coding month (60M in, 10M out) | $600.00 | $180.00 |
On a typical 75/25 input-output mix, Grok 4.5 costs less (about 73% 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": "openai/gpt-5.5", "messages": [{"role": "user", "content": "Hello"}]}'
# the other one: change the model string
-d '{"model": "x-ai/grok-4.5", ...}'Common questions
Which is cheaper, GPT 5.5 or Grok 4.5?
Grok 4.5 is cheaper on a typical mix of 75% input and 25% output tokens, by about 73%. 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. Grok 4.5 offers 500K tokens.
Can I switch between GPT 5.5 and Grok 4.5 without changing code?
Yes. Both are callable at https://rapidrouter.ai/api/v1 with the same OpenAI-compatible request; only the model string changes (openai/gpt-5.5 or x-ai/grok-4.5).
How do I pay for GPT 5.5 or Grok 4.5?
Top up a Rapid Router balance by card in US dollars, and both models debit that balance per request.
More GPT models: OpenAI API pricing · More Grok: xAI API pricing