Model comparison
Claude Opus 5.5 vs Kimi K3
Claude Opus 5.5 (Anthropic) and Kimi K3 (Moonshot) 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.
| Claude Opus 5.5 | Kimi K3 | |
|---|---|---|
| Input price per 1M | $4.00 | $0.304 |
| Output price per 1M | $20.00 | $11.94 |
| Context window | 1M tokens | 1M tokens |
| Max output | 128K tokens | 131K tokens |
| Input types | text, image, pdf | text, image, video |
| Capabilities | tools, JSON, vision, reasoning | tools, JSON, vision, reasoning |
| Author | Anthropic | Moonshot |
| LMArena Overall | 1516 | 1475 |
| LMArena Coding | 1545 | 1507 |
| LMArena Math | 1508 | 1494 |
| LMArena Creative writing | 1534 | 1456 |
| LMArena Instruction following | 1536 | 1483 |
| LMArena Hard prompts | 1535 | 1494 |
| LMArena Vision | 1321 | — |
| LMArena Web dev | 1811 | 1655 |
| GPQA Diamond | 90.6% | 93.1% |
| OTIS Mock AIME | 100.0% | 97.2% |
| SimpleQA Verified | 72.2% | 50.6% |
Scores from LMArena and Epoch AI, as published; a blank cell means not measured there.
What a month costs on each
| Workload | Claude Opus 5.5 | Kimi K3 |
|---|---|---|
| Chatbot month (15M in, 4M out) | $140.00 | $52.30 |
| RAG month (40M in, 3M out) | $220.00 | $47.97 |
| Coding month (60M in, 10M out) | $440.00 | $137.60 |
On a typical 75/25 input-output mix, Kimi K3 costs less (about 60% less than Claude Opus 5.5). Kimi K3 takes the longer prompt at 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": "anthropic/claude-opus-5-5", "messages": [{"role": "user", "content": "Hello"}]}'
# the other one: change the model string
-d '{"model": "moonshotai/kimi-k3", ...}'Common questions
Which is cheaper, Claude Opus 5.5 or Kimi K3?
Kimi K3 is cheaper on a typical mix of 75% input and 25% output tokens, by about 60%. Through Rapid Router both are billed at the provider list price per million tokens.
Which has the larger context window?
Kimi K3, at 1M tokens. Claude Opus 5.5 offers 1M tokens.
Can I switch between Claude Opus 5.5 and Kimi K3 without changing code?
Yes. Both are callable at https://rapidrouter.ai/api/v1 with the same OpenAI-compatible request; only the model string changes (anthropic/claude-opus-5-5 or moonshotai/kimi-k3).
How do I pay for Claude Opus 5.5 or Kimi K3?
Top up a Rapid Router balance by card in US dollars, and both models debit that balance per request.
More Claude models: Anthropic API pricing · More Kimi: Moonshot API pricing