Comparison · Chat & code
Kimi K3 vs Claude Opus 5.5
Kimi K3 vs Claude Opus 5.5 for long coding sessions: rates, cached input, image and video input, open weights and Claude Code support. Which one to use.
What each one accepts
| Kimi K3 | Claude Opus 5.5 | |
|---|---|---|
| Vendor | Moonshot AI | Anthropic |
| Type | Chat & code | Chat & code |
| Released | 2026-07 | 2026-09 |
| Context window | 1,048,576 tokens | 1,000,000 tokens |
| Max output | 131,072 tokens | 128,000 tokens |
| Endpoints | /v1/chat/completions | /v1/chat/completions · /v1/messages |
Token prices
| Kimi K3 | Claude Opus 5.5 | |
|---|---|---|
| Input / 1M tokens | $3.38 | $3.78 |
| Output / 1M tokens | $16.88 | $18.90 |
| Input from cache / 1M | $0.338 | $0.189 |
| 1,000 replies, 1,500 in / 400 out | $11.81 | $13.23 |
Charged from a prepaid USD balance, no taxes added. One key runs both, through /v1/chat/completions in the OpenAI format. A failed generation is $0.
Kimi K3 makes sense if you want open weights for long coding sessions, if your agent must also read screenshots or video, or if a long prefix repeats on every call. Its token rates sit a little below Opus 5.5, and its cached input is cheap. Claude Opus 5.5 is the pick for Claude Code and sweeping repository changes. Moonshot openly says K3 still trails the strongest closed models, so the real question is whether that gap shows on your own work.
When to pick Kimi K3
- You run long sessions in a large repository with build and test loops in the terminal, through Cursor or Cline.
- Your agent receives screenshots or screen recordings of a bug next to the code.
- Many requests share one long prefix and you want cached reads to keep the bill down.
- Your team prefers an open-weight model and may host it later.
When to pick Claude Opus 5.5
- An agent session in Claude Code should last for hours.
- A refactor or migration reaches hundreds of files.
- The spec is vague and you would rather the model ask before it edits code.
- Your codebase already talks to the Anthropic SDK, so only the base URL and key change.
Differences you will notice
- Rates. Kimi K3 is billed at $3.38 / $16.88 per 1M tokens, Claude Opus 5.5 at $3.78 / $18.90 per 1M tokens. Kimi is the cheaper of the two on regular input and output; compare the cached input row in the table above if your prompts repeat.
- Where they plug in. Opus answers on
/v1/chat/completionsand/v1/messages, so Claude Code can drive it. Kimi K3 uses the OpenAI-compatible endpoint only: Cursor, Cline and Continue work, Claude Code does not. - Weights and input types. Kimi K3 is an open mixture-of-experts model with 2.8T parameters in total; self-hosting still means server hardware. Moonshot says it reads images and video natively. Opus 5.5 is closed.
- Behavior notes. Moonshot warns that K3 tends to act instead of asking when a task is ambiguous, and gets worse when a tool trims its reasoning. Opus 5.5 always thinks, and those tokens are billed as output.
- Limits. Kimi K3: 1,048,576 tokens in, up to 131,072 out. Opus 5.5: 1,000,000 in, up to 128K out. In practice that is a draw.
How to decide
Run one real task from your repository through both and compare the diff and the usage field; the shared key and balance make that a five-minute job. I have not measured this pair on Polish text, and Moonshot admits K3 lacks the conversational polish of top closed models, so if people will read the output, test a dozen of your own samples too. All current pairs are on the comparisons page, and the cost ranking is in Cheapest LLM API.
Questions
How do I call Kimi K3 from Cursor or Cline?
Set the OpenAI-compatible base URL to https://kadraris.com/v1, paste your sk-kd- key and choose the model kimi-k3.
Which one is better for a vague ticket?
Based on Moonshot's own notes, Opus 5.5 is the safer bet when you want questions before changes, since K3 leans toward acting. Check that on your own tickets.
Is there a subscription for either model?
No. Both draw from one prepaid balance that does not expire, with no monthly fee.