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.
- For the same tokens
- The same price, $2 in and $10 out
- Cheaper to read
- Neither, both $2
- Cheaper to write
- Neither, both $10
- Scores higher
- Not known, Kimi K3.1 Pro has no independent score yet
- Larger window
- Kimi K3.1 Pro, 1.05M against 1M tokens
Price per million tokens, side by side
In US dollars, as each maker prints them. The better figure in each row is green.
| Claude Sonnet 5.5Anthropic | Kimi K3.1 ProMoonshot AI | |
|---|---|---|
| InputTokens the model reads | $2 | $2 |
| Cached inputRead again from the cache | $0.10 | $0.20 |
| Cache writePutting text in the cache | $2.50 | $2 |
| OutputTokens it writes, thinking included | $10 | $10 |
| Blend 3:13 tokens read for each 1 written | $4 | $4 |
| Batch inputAnswers collected later | $1 | Not listed |
| Batch output | $5 | Not listed |
| Context windowTokens it holds at once | 1M | 1.05M |
| Capability scoreEpoch Capabilities Index; GPT-5 is 150 | 164 | Not listed |
| Longest answerTokens it writes in 1 reply | 128K | Not listed |
Price changes
- 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. What changed
The same text, counted by each maker
A price per token means little until you know how many tokens your text is. Here is our lesson How AI writes, about 1,700 words of English, counted the way each maker counts it, and what it costs to send it once.
Claude Sonnet 5.5
about 2,100 to 3,600 tokens
Sent once: 0.41 cents to 0.72 cents at $2 per million
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
Sent once: 0.41 cents at $2 per million
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 number of runs a day, for 30 days, at the standard price. The cheaper of the 2 is green; open any job in the calculator to change it. Sizes are in tokens, and Claude Sonnet 5.5 can need up to 1.7 times as many as Kimi K3.1 Pro for the same words, so its bill for the same work can be up to that much higher.
| Job | Claude Sonnet 5.5 | Kimi K3.1 Pro | Difference |
|---|---|---|---|
| A chat question300 in, 500 out, 100 a day | $16.800.56 cents a run | $16.800.56 cents a run | The same |
| A hard question, with thinking300 in, 1,400 out, 100 a day | $43.801.5 cents a run | $43.801.5 cents a run | The same |
| A long report, summarised60,000 in, 2,000 out, 20 a day | $84.0014 cents a run | $84.0014 cents a run | The same |
| A 40-turn agent task2,800,000 in, 40,000 out, 10 a day | $364$1.21 a run | $439$1.46 a run | 1.2 times |
| A support bot's reply4,000 in, 300 out, 2,000 a day | $4320.72 cents a run | $4440.74 cents a run | 1 times |
| Sort a message into a category250 in, 5 out, 50,000 a day | $8250.055 cents a run | $8250.055 cents a run | The same |
| Read an invoice into fields1,500 in, 250 out, 1,000 a day | $1650.55 cents a run | $1650.55 cents a run | The same |
| Review a pull request25,000 in, 4,500 out, 50 a day | $1439.5 cents a run | $1439.5 cents a run | The same |
Your own job on both
Start from a job, then set its size, how often it runs and whether the answers can wait. Both bills follow every change.
A short question and a few paragraphs back.
about 230 words
Instructions or documents the model has read before cost far less the second time.
about 380 words
A month of this job
- Claude Sonnet 5.5$16.80
0.56 cents a run
- Kimi K3.1 Pro$16.80
0.56 cents a run
The 2 cost the same for this job, counted in tokens.
This job on every modelWhy the price per token is only the start
Every maker prints 2 main prices: one for the tokens a model reads (input) and one for the tokens it writes (output). On most current models writing costs 3 to 5 times as much as reading, so which model is cheaper can depend on the job. A job that reads a long document and writes a line pays mostly the input price; a chat that writes paragraphs pays mostly the output price. That is why each comparison prices 8 jobs and not one figure.
The same text is not the same number of tokens on every model. Each maker cuts text its own way, and Anthropic says its models from Claude 4.7 on produce about 30 percent more tokens for the same text than earlier ones. A model with the lower price per token can still send the larger bill, so each comparison counts one of our lessons the way both makers count it.
Discounts change the order too. Work that can wait costs half on a batch at the makers that offer one, and text read again from a cache costs a quarter of the input price or less on every current model here. The price table on each comparison shows who offers what.
Thinking is billed as output, and models differ in how much they think and how long they answer. A price list cannot show that. Before you switch, run the same 10 tasks on both models and compare the bills.
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