# Claude Sonnet 5.5 vs Kimi K3.1 Pro

Claude Sonnet 5.5 and Kimi K3.1 Pro charge the same per token: $2 per million tokens read and $10 per million written. The bill can still differ, because the same text can be a different number of tokens on each. Below are both price lists, 8 everyday jobs priced on each, and the count for one text.

- Page, with a calculator for your own job: https://tecyfy.com/prices/compare/claude-sonnet-5-5-vs-kimi-k3-1-pro
- Makers: Claude Sonnet 5.5 from Anthropic, Kimi K3.1 Pro from Moonshot AI

## Price per million tokens, in US dollars

| | Claude Sonnet 5.5 | Kimi K3.1 Pro |
| --- | --: | --: |
| Input | $2 | $2 |
| Cached input | $0.10 | $0.20 |
| Cache write | $2.50 | $2 |
| Output | $10 | $10 |
| Blend, 3 read for each 1 written | $4 | $4 |
| Batch input | $1 | not listed |
| Batch output | $5 | not listed |
| Context window, tokens | 1M | 1.05M |
| Capability score (Epoch Capabilities Index; GPT-5 is 150) | 164 | not listed |
| Longest answer, tokens | 128K | not listed |

Price change, Claude Sonnet 5.5: Cached input went from $0.20 to $0.10 per million tokens. The price of a cache write did not change.

## The same text, counted by each maker

Our lesson "How AI writes" (https://tecyfy.com/learn/how-ai-works/how-ai-writes), about 1,700 words of English:

- Claude Sonnet 5.5: about 2,100 to 3,600 tokens. Anthropic does not publish its tokenizer. It says Claude 4.7 and later produce about 30 percent more tokens for the same text than earlier models, and an independent test counted TypeScript at 1.73 times OpenAI's figure. The range runs from OpenAI's count to 1.75 times it.
- Kimi K3.1 Pro: about 2,100 tokens. Counted with the tokenizer Moonshot AI publishes with Kimi K3, the model its API serves.

## What 8 everyday jobs cost a month on each

Each job at its usual runs a day, for 30 days, at the standard price.

| Job | Tokens in, out, runs a day | Claude Sonnet 5.5 | Kimi K3.1 Pro |
| --- | --- | --: | --: |
| A chat question | 300, 500, 100 | $16.80 | $16.80 |
| A hard question, with thinking | 300, 1,400, 100 | $43.80 | $43.80 |
| A long report, summarised | 60,000, 2,000, 20 | $84.00 | $84.00 |
| A 40-turn agent task | 2,800,000, 40,000, 10 | $364 | $439 |
| A support bot's reply | 4,000, 300, 2,000 | $432 | $444 |
| Sort a message into a category | 250, 5, 50,000 | $825 | $825 |
| Read an invoice into fields | 1,500, 250, 1,000 | $165 | $165 |
| Review a pull request | 25,000, 4,500, 50 | $143 | $143 |

## Questions

### Which is cheaper, Claude Sonnet 5.5 or Kimi K3.1 Pro?

Per token, neither: both charge $2 per million tokens read and $10 per million written. The same text can still be a different number of tokens on each, so the bills can differ.

### Which is better, Claude Sonnet 5.5 or Kimi K3.1 Pro?

Claude Sonnet 5.5 scores 164 on the Epoch Capabilities Index, an independent score from Epoch AI that combines over 50 benchmarks (GPT-5 is 150). Kimi K3.1 Pro has no independent score yet, so the only fair test is to run the same 10 tasks on both.

### What does a support bot cost a month on Claude Sonnet 5.5 and Kimi K3.1 Pro?

At 2,000 replies a day, each reading 4,000 tokens (50 percent of them from cache) and writing 300, it costs $432 a month on Claude Sonnet 5.5 and $444 on Kimi K3.1 Pro: Kimi K3.1 Pro costs 1 times as much for this job.

### What does an AI agent task cost on Claude Sonnet 5.5 and Kimi K3.1 Pro?

One 40-turn task that reads 2,800,000 tokens in all, 90 percent of them from cache, and writes 40,000, costs $1.21 on Claude Sonnet 5.5 and $1.46 on Kimi K3.1 Pro. At 10 tasks a day that is $364 and $439 a month.

### Which has the larger context window, Claude Sonnet 5.5 or Kimi K3.1 Pro?

Kimi K3.1 Pro, with 1.05M tokens against 1M on Claude Sonnet 5.5. The window holds your instructions, the files you attach, the conversation so far and the answer, all at once.

### Does the same text take the same number of tokens on Claude Sonnet 5.5 and Kimi K3.1 Pro?

No. Our lesson "How AI writes", 1,700 words long, is about 2,100 to 3,600 tokens on Claude Sonnet 5.5 and about 2,100 on Kimi K3.1 Pro. Each maker cuts text its own way, and every extra token is paid for at the model's price.

### Can I pay less on Claude Sonnet 5.5 and Kimi K3.1 Pro for work that can wait?

On Claude Sonnet 5.5 only: with a batch, where you collect the answers later, it costs $1 per million tokens read and $5 written. Moonshot AI's price page lists no batch price for Kimi K3.1 Pro.

## Sources

- [Anthropic: API prices](https://platform.claude.com/docs/en/about-claude/pricing)
- [Moonshot AI: API prices](https://platform.kimi.ai/docs/pricing/chat)
- [Epoch Capabilities Index, by Epoch AI (CC BY 4.0)](https://epoch.ai/benchmarks/eci)

## Other comparisons

- [Claude Mythos 5.1 vs Claude Sonnet 5.5](https://tecyfy.com/prices/compare/claude-mythos-5-1-vs-claude-sonnet-5-5.md)
- [Claude Fable 5 vs Claude Sonnet 5.5](https://tecyfy.com/prices/compare/claude-fable-5-vs-claude-sonnet-5-5.md)
- [Claude Mythos 5 vs Claude Sonnet 5.5](https://tecyfy.com/prices/compare/claude-mythos-5-vs-claude-sonnet-5-5.md)
- [Claude Opus 5 vs Claude Sonnet 5.5](https://tecyfy.com/prices/compare/claude-opus-5-vs-claude-sonnet-5-5.md)
- [Claude Opus 4.8 vs Claude Sonnet 5.5](https://tecyfy.com/prices/compare/claude-opus-4-8-vs-claude-sonnet-5-5.md)
- [Claude Opus 4.7 vs Claude Sonnet 5.5](https://tecyfy.com/prices/compare/claude-opus-4-7-vs-claude-sonnet-5-5.md)