Kimi K3 vs Claude Opus 5.5: API Price for Long-Running Coding Agents
By Nicho
Moonshot AI describes Kimi K3 as its flagship open-weight model for long-horizon coding, knowledge work and deep reasoning. Anthropic describes Claude Opus 5.5 as its model for long-running agentic coding and knowledge work. They are built for the same jobs, so the price comparison is a fair one.
This post compares published prices checked on 27 October 2026. It does not include benchmark results. Run your own evaluation before you move production traffic.
Prices per million tokens
| Model and route | Input / 1M | Cache read / 1M | Output / 1M |
|---|---|---|---|
| Claude Opus 5.5, Anthropic API | $4.00 | $0.20 | $20.00 |
| Claude Sonnet 5.5, Anthropic API | $2.00 | $0.10 | $10.00 |
| Kimi K3, Moonshot list price | $3.00 | — | $15.00 |
| Kimi K3, cheapaimodel | $2.093511 | $0.209351 | $10.467555 |
Through cheapaimodel, Kimi K3 costs about 48% less than Claude Opus 5.5 on both input and output tokens.
Claude Sonnet 5.5 is in the table for a reason. Anthropic positions it as the faster, lower-cost model for well-scoped everyday tasks, and it is about 5% cheaper per token than Kimi K3 on cheapaimodel. If your work fits Sonnet, Kimi K3 is not the cheaper option.
What a workload costs
| Workload | Kimi K3 on cheapaimodel | Claude Opus 5.5 | Claude Sonnet 5.5 |
|---|---|---|---|
| 1M input + 0.2M output | $4.1870 | $8.0000 | $4.0000 |
| 20M input + 4M output | $83.7404 | $160.0000 | $80.0000 |
| 4M input + 16M cache reads + 2M output | $32.6588 | $59.2000 | $29.6000 |
The cached scenario assumes an 80% cache-hit share. Anthropic also charges for cache writes ($5 per million tokens on Opus 5.5 for a 5-minute cache), which this table leaves out. Anthropic's Batch API is 50% off; if your jobs can wait for batch results, Opus 5.5 drops to $2 / $10 per million tokens. cheapaimodel does not offer a batch API.
Limits and inputs
| Kimi K3 | Claude Opus 5.5 | |
|---|---|---|
| Context window | 1M tokens | 1M tokens |
| Max output | Up to 1,048,576 tokens, sharing the context window | 128K tokens (300K on the Batch API with a beta header) |
| Input types | Text, image, video | Text, image |
| Weights | Open, under the Kimi K3 License | Closed |
The Kimi K3 License is based on MIT. It adds one condition: a model-as-a-service business with more than $20 million in revenue over 12 months needs a separate agreement with Moonshot AI. That matters only if you plan to host the weights yourself at that scale.
When to choose which
Choose Kimi K3 when:
- You want flagship-class long-horizon work at about half the price of Opus 5.5.
- You need video input or very long single outputs.
- You want the option to self-host the same open weights later.
- You already call other open models through one OpenAI-compatible API.
Choose Claude Opus 5.5 when:
- Your own evaluations show Opus 5.5 does the job better and the quality gap is worth paying for.
- You depend on Anthropic-specific features, such as its server tools, the Messages API or batch processing.
- You need Claude on a specific cloud platform, such as Amazon Bedrock.
If the work is well scoped and Sonnet 5.5 passes your evaluations, it is the price peer to Kimi K3. Compare the two on your own prompts.
Try Kimi K3
Kimi K3 works with any OpenAI SDK. Set the base URL to https://api.cheapaimodel.ai/v1 and the model to kimi-k3. See the quickstart, the Kimi K3 model page for live prices, or all open-source models.
Sources: Anthropic pricing, Anthropic models overview, Kimi K3 quickstart, Kimi K3 weights.