# Claude Mythos 5.1 vs Claude Sonnet 5.5

Claude Sonnet 5.5 is one of Anthropic's newest models and Claude Mythos 5.1 an earlier one, so this is also what moving up costs or saves. Claude Sonnet 5.5 is the cheaper of the 2: for the same tokens, 3 read for each 1 written, Claude Mythos 5.1 costs 5 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/claude-mythos-5-1-vs-claude-sonnet-5-5
- Makers: Claude Mythos 5.1 from Anthropic, Claude Sonnet 5.5 from Anthropic

## Price per million tokens, in US dollars

| | Claude Mythos 5.1 | Claude Sonnet 5.5 |
| --- | --: | --: |
| Input | $10 | $2 |
| Cached input | $0.25 | $0.10 |
| Cache write | $12.50 | $2.50 |
| Output | $50 | $10 |
| Blend, 3 read for each 1 written | $20 | $4 |
| Batch input | $5 | $1 |
| Batch output | $25 | $5 |
| Context window, tokens | 1M | 1M |
| Capability score (Epoch Capabilities Index; GPT-5 is 150) | not listed | 164 |
| Longest answer, tokens | 128K | 128K |

Claude Mythos 5.1: Limited availability.

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.

## 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 Mythos 5.1 | Claude Sonnet 5.5 |
| --- | --- | --: | --: |
| A chat question | 300, 500, 100 | $84.00 | $16.80 |
| A hard question, with thinking | 300, 1,400, 100 | $219 | $43.80 |
| A long report, summarised | 60,000, 2,000, 20 | $420 | $84.00 |
| A 40-turn agent task | 2,800,000, 40,000, 10 | $1,629 | $364 |
| A support bot's reply | 4,000, 300, 2,000 | $2,130 | $432 |
| Sort a message into a category | 250, 5, 50,000 | $4,125 | $825 |
| Read an invoice into fields | 1,500, 250, 1,000 | $825 | $165 |
| Review a pull request | 25,000, 4,500, 50 | $713 | $143 |

## Questions

### Which is cheaper, Claude Mythos 5.1 or Claude Sonnet 5.5?

Claude Sonnet 5.5 is cheaper: $2 per million tokens read and $10 per million written, against $10 and $50 on Claude Mythos 5.1. On a mix of 3 tokens read for each 1 written, Claude Mythos 5.1 costs 5 times as much.

### Which is better, Claude Mythos 5.1 or Claude Sonnet 5.5?

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). Claude Mythos 5.1 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 Mythos 5.1 and Claude Sonnet 5.5?

At 2,000 replies a day, each reading 4,000 tokens (50 percent of them from cache) and writing 300, it costs $2,130 a month on Claude Mythos 5.1 and $432 on Claude Sonnet 5.5: Claude Mythos 5.1 costs 4.9 times as much for this job.

### What does an AI agent task cost on Claude Mythos 5.1 and Claude Sonnet 5.5?

One 40-turn task that reads 2,800,000 tokens in all, 90 percent of them from cache, and writes 40,000, costs $5.43 on Claude Mythos 5.1 and $1.21 on Claude Sonnet 5.5. At 10 tasks a day that is $1,629 and $364 a month.

### Which has the larger context window, Claude Mythos 5.1 or Claude Sonnet 5.5?

Neither: both hold 1M tokens at once, about 1,500 pages of English text.

### Does the same text take the same number of tokens on Claude Mythos 5.1 and Claude Sonnet 5.5?

Yes, both are counted the same way: our lesson "How AI writes", 1,700 words long, is about 2,100 to 3,600 tokens on each.

### Is it cheaper to move from Claude Mythos 5.1 to Claude Sonnet 5.5?

Yes, per token: Claude Sonnet 5.5 costs $2 per million tokens read and $10 written, against $10 and $50 on Claude Mythos 5.1, which costs 5 times as much for the same tokens. Run your own tasks on it before you switch, since answers, length and thinking can differ.

### Can I pay less on Claude Mythos 5.1 and Claude Sonnet 5.5 for work that can wait?

Yes, on both. With a batch, where you collect the answers later instead of at once, Claude Mythos 5.1 costs $5 per million tokens read and $25 written, and Claude Sonnet 5.5 $1 and $5.

## Sources

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

## Other comparisons

- [Claude Fable 5.1 vs Claude Mythos 5.1](https://tecyfy.com/prices/compare/claude-fable-5-1-vs-claude-mythos-5-1.md)
- [Claude Mythos 5.1 vs Claude Opus 5.5](https://tecyfy.com/prices/compare/claude-mythos-5-1-vs-claude-opus-5-5.md)
- [Claude Haiku 5.5 vs Claude Mythos 5.1](https://tecyfy.com/prices/compare/claude-haiku-5-5-vs-claude-mythos-5-1.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)