# GPT-6 Luna vs Kimi K3

GPT-6 Luna is the cheaper of the 2: for the same tokens, 3 read for each 1 written, Kimi K3 costs 30 times as much. Below are both price lists, what 8 everyday jobs cost a month on each, and how many tokens the same text takes on each, which can change the answer.

- Page, with a calculator for your own job: https://tecyfy.com/prices/compare/gpt-6-luna-vs-kimi-k3
- Makers: GPT-6 Luna from OpenAI, Kimi K3 from Moonshot AI

## Price per million tokens, in US dollars

| | GPT-6 Luna | Kimi K3 |
| --- | --: | --: |
| Input | $0.10 | $3 |
| Cached input | $0.01 | $0.30 |
| Cache write | $0.125 | $3 |
| Output | $0.50 | $15 |
| Blend, 3 read for each 1 written | $0.20 | $6 |
| Batch input | $0.05 | not listed |
| Batch output | $0.25 | not listed |
| Long prompt input (above 272K on GPT-6 Luna) | $0.20 | $3 |
| Long prompt output | $0.75 | $15 |
| Context window, tokens | 1.05M | 1.05M |
| Capability score (Epoch Capabilities Index; GPT-5 is 150) | 156 | 157 |
| Longest answer, tokens | 128K | not listed |

## 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:

- GPT-6 Luna: about 2,100 tokens. GPT-5.6 is counted with o200k_base, the tokenizer OpenAI publishes for it, so its count is exact. OpenAI has not published the tokenizer of GPT-6, so its count is the same o200k_base figure, marked as about.
- Kimi K3: 2,055 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 | GPT-6 Luna | Kimi K3 |
| --- | --- | --: | --: |
| A chat question | 300, 500, 100 | 84 cents | $25.20 |
| A hard question, with thinking | 300, 1,400, 100 | $2.19 | $65.70 |
| A long report, summarised | 60,000, 2,000, 20 | $4.20 | $126 |
| A 40-turn agent task | 2,800,000, 40,000, 10 | $21.96 | $659 |
| A support bot's reply | 4,000, 300, 2,000 | $22.20 | $666 |
| Sort a message into a category | 250, 5, 50,000 | $41.25 | $1,238 |
| Read an invoice into fields | 1,500, 250, 1,000 | $8.25 | $248 |
| Review a pull request | 25,000, 4,500, 50 | $7.13 | $214 |

## Questions

### Which is cheaper, GPT-6 Luna or Kimi K3?

GPT-6 Luna is cheaper: $0.10 per million tokens read and $0.50 per million written, against $3 and $15 on Kimi K3. On a mix of 3 tokens read for each 1 written, Kimi K3 costs 30 times as much.

### Which is better, GPT-6 Luna or Kimi K3?

They cannot be told apart on the Epoch Capabilities Index, an independent score from Epoch AI that combines over 50 benchmarks: GPT-6 Luna scores 156 and Kimi K3 157, within the range of doubt around each (GPT-5 is 150). So choose on price and on 10 tasks of your own.

### What does a support bot cost a month on GPT-6 Luna and Kimi K3?

At 2,000 replies a day, each reading 4,000 tokens (50 percent of them from cache) and writing 300, it costs $22.20 a month on GPT-6 Luna and $666 on Kimi K3: Kimi K3 costs 30 times as much for this job.

### What does an AI agent task cost on GPT-6 Luna and Kimi K3?

One 40-turn task that reads 2,800,000 tokens in all, 90 percent of them from cache, and writes 40,000, costs 7.3 cents on GPT-6 Luna and $2.20 on Kimi K3. At 10 tasks a day that is $21.96 and $659 a month.

### Which has the larger context window, GPT-6 Luna or Kimi K3?

GPT-6 Luna, with 1.05M tokens against 1.05M on Kimi K3. 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 GPT-6 Luna and Kimi K3?

No. Our lesson "How AI writes", 1,700 words long, is about 2,100 tokens on GPT-6 Luna and 2,055 on Kimi K3. Each maker cuts text its own way, and every extra token is paid for at the model's price.

### Can I pay less on GPT-6 Luna and Kimi K3 for work that can wait?

On GPT-6 Luna only: with a batch, where you collect the answers later, it costs $0.05 per million tokens read and $0.25 written. Moonshot AI's price page lists no batch price for Kimi K3.

## Sources

- [OpenAI: API prices](https://developers.openai.com/api/docs/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

- [GPT-6 Luna vs GPT-6 Sol](https://tecyfy.com/prices/compare/gpt-6-luna-vs-gpt-6-sol.md)
- [GPT-5.6 Sol vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-6-sol-vs-gpt-6-luna.md)
- [GPT-5.6 Terra vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-6-terra-vs-gpt-6-luna.md)
- [GPT-5.6 Luna vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-6-luna-vs-gpt-6-luna.md)
- [GPT-5.5 vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-5-vs-gpt-6-luna.md)
- [GPT-5.5 pro vs GPT-6 Luna](https://tecyfy.com/prices/compare/gpt-5-5-pro-vs-gpt-6-luna.md)