Comparison · Chat & code models
Kimi K3 vs Claude Opus 5.5
Kimi K3 or Claude Opus 5.5? Kimi is about 25% cheaper, has open weights and cheap caching, Opus runs in Claude Code. Differences and which to use for code.
Specs side by side
| 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 |
Price per token
| Kimi K3 | Claude Opus 5.5 | |
|---|---|---|
| Input / 1M tokens | $4.05 | $5.40 |
| Output / 1M tokens | $20.25 | $27.00 |
| Cached input / 1M | $0.405 | input rate |
| 1,000 replies (1,500 in + 400 out) | $14.18 | $18.90 |
Prices exclude taxes and are charged from your prepaid USD balance. Both models work through the same key, in the OpenAI-compatible /v1/chat/completions endpoint. Failed generations cost nothing.
Use Kimi K3 when you want an open-weights model for long coding sessions, when your agent also has to look at screenshots or video, or when you keep sending the same long prefix: per token it is about 25% cheaper, and its cached input is very cheap. Use Claude Opus 5.5 for Claude Code and large repository changes. Moonshot itself says K3 still trails the strongest closed models, so the choice comes down to whether that gap shows up on your own tasks.
Key differences
- Price. Kimi K3 costs $4.05 / $20.25 per 1M tokens, Claude Opus 5.5 costs $5.40 / $27.00 per 1M tokens. Opus is about 1.33 times more on both input and output, so Kimi comes out about 25% cheaper, including the 1,000-reply row in the table above.
- Caching. Kimi K3 has a cached-input rate on Jantaris ten times lower than its own input. Claude has no such line, so a repeated prefix is billed as input. With a long, stable system prompt, Kimi's lead grows several times over.
- Context. Kimi K3: 1,048,576 tokens and up to 131,072 output tokens. Opus 5.5: 1,000,000 and up to 128K. No practical difference.
- Claude Code. Opus works on
/v1/chat/completionsand on/v1/messages, so it runs in Claude Code. Kimi K3 runs on the OpenAI-compatible endpoint: Cursor, Cline or Continue yes, Claude Code through Jantaris no. - Open weights. Kimi K3 is a mixture-of-experts model with open weights and 2.8T parameters in total. Opus 5.5 is closed. Self-hosting Kimi still means server hardware, not a home GPU.
- Polish and other languages. I have not measured this pair on Polish text. Moonshot admits K3 lacks the conversational polish of the best closed models, so for text meant for people, check both on a dozen of your own examples.
- Multimodal input. Moonshot says Kimi K3 natively understands images and video. That helps agents that get screenshots or screen recordings of a bug.
- Vendor caveats. According to Moonshot, in ambiguous situations K3 tends to act rather than ask, and loses quality when a tool trims its reasoning. On Opus 5.5, in turn, thinking cannot be switched off, and thinking tokens are billed as output.
When to pick Kimi K3
- Long sessions in large repositories with a build-and-test loop in the terminal, in Cursor or Cline.
- Agents that get screenshots or video in addition to code.
- Requests with the same long prefix, where cheap cached input matters.
- Teams that want an open-weights model and maybe self-hosting later.
When to pick Claude Opus 5.5
- Agent sessions in Claude Code that run for hours.
- Refactors and migrations that touch hundreds of files.
- Tasks with a vague spec, where you would rather the model asked before changing code.
- Code already written for the Anthropic SDK: you change only the base URL and key.
Both models sit behind one key and one balance that never expires, with no subscription, so the simplest test is to run the same task from your repository through both and compare the changes and the usage field. Currently available pairs are listed in model comparisons, and the cost ranking in Cheapest LLM API.
FAQ
Kimi K3 or Claude Opus 5.5 for coding?
For work in Claude Code, Opus 5.5, because of the two only Opus works through /v1/messages. In Cursor, Cline or your own agent you can use either. I have not tested this pair on my own code, so run a dozen tasks from your repository through both and compare the result and the cost.
How much cheaper is Kimi K3 than Opus 5.5?
About 25% on every input and output token. With a repeated prefix the gap is much wider, because Kimi has a separate low cached-input rate. Current rates: $4.05 / $20.25 per 1M tokens and $5.40 / $27.00 per 1M tokens.
Can I use Kimi K3 in Claude Code?
Not through Jantaris. The Anthropic-compatible endpoint that Claude Code uses serves Claude models only. Use Kimi K3 in OpenAI-compatible tools with base URL https://jantaris.com/v1 and model kimi-k3.