# What's new in Claude Sonnet 5

> Source: <https://simonwillison.net/2026/Jun/30/claude-sonnet-5/#atom-everything>
> Published: 2026-06-30 21:23:02+00:00

Anthropic say of Sonnet 5 that "its performance is close to that of Opus 4.8, but at lower prices". The [system card](https://www-cdn.anthropic.com/9e6a1044980d8c4ed85669faf9c2a8342e2e9f1e/Claude%20Sonnet%205%20System%20Card.pdf) helps explain how they were able to release the model without being blocked by the US government:

Sonnet 5 is significantly less capable at cyber tasks than Mythos 5: its safeguards are thus similar to those we apply to Opus 4.7 and Opus 4.8 (models that are more capable than Sonnet 5 but much less capable than Mythos 5).

Of note from the "what's new" API changes:

`temperature`

, `top_p`

, `top_k`

are no longer supported.`"thinking": {type: "disabled"}`

.I used my [Claude Token Counter](https://tools.simonwillison.net/claude-token-counter) tool to try out the new tokenizer. Here are my results for several larger documents:

| Document | Sonnet 4.6 | Opus 4.7 | Sonnet 5 |
|---|---|---|---|
|

So the new token is roughly 1.4x times more expensive for English, 1.33x for Spanish, 1.28x for Python code and effectively the same cost for Simplified Mandarin.

Here's [the pelican](https://gist.github.com/simonw/a89e756b621a31e8ffc210e3428efa77). It's nothing to write home about. Sonnet 5 thinks it looks like a goose.

Via [Hacker News](https://news.ycombinator.com/item?id=48736605)

Tags: [ai](https://simonwillison.net/tags/ai), [generative-ai](https://simonwillison.net/tags/generative-ai), [llms](https://simonwillison.net/tags/llms), [anthropic](https://simonwillison.net/tags/anthropic), [claude](https://simonwillison.net/tags/claude), [llm-pricing](https://simonwillison.net/tags/llm-pricing), [pelican-riding-a-bicycle](https://simonwillison.net/tags/pelican-riding-a-bicycle), [llm-release](https://simonwillison.net/tags/llm-release)