{"slug": "what-s-new-in-claude-sonnet-5", "title": "What's new in Claude Sonnet 5", "summary": "Anthropic released Claude Sonnet 5, a new AI model with performance close to Opus 4.8 at lower prices, and updated its API by removing temperature, top_p, and top_k parameters. The model's tokenizer is roughly 1.4x more expensive for English text compared to previous versions.", "body_md": "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:\n\nSonnet 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).\n\nOf note from the \"what's new\" API changes:\n\n`temperature`\n\n, `top_p`\n\n, `top_k`\n\nare no longer supported.`\"thinking\": {type: \"disabled\"}`\n\n.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:\n\n| Document | Sonnet 4.6 | Opus 4.7 | Sonnet 5 |\n|---|---|---|---|\n|\n\nSo 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.\n\nHere's [the pelican](https://gist.github.com/simonw/a89e756b621a31e8ffc210e3428efa77). It's nothing to write home about. Sonnet 5 thinks it looks like a goose.\n\nVia [Hacker News](https://news.ycombinator.com/item?id=48736605)\n\nTags: [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)", "url": "https://wpnews.pro/news/what-s-new-in-claude-sonnet-5", "canonical_source": "https://simonwillison.net/2026/Jun/30/claude-sonnet-5/#atom-everything", "published_at": "2026-06-30 21:23:02+00:00", "updated_at": "2026-06-30 21:49:07.648983+00:00", "lang": "en", "topics": ["large-language-models", "ai-products", "ai-tools"], "entities": ["Anthropic", "Claude Sonnet 5", "Opus 4.8", "Mythos 5", "Opus 4.7", "Claude Token Counter"], "alternates": {"html": "https://wpnews.pro/news/what-s-new-in-claude-sonnet-5", "markdown": "https://wpnews.pro/news/what-s-new-in-claude-sonnet-5.md", "text": "https://wpnews.pro/news/what-s-new-in-claude-sonnet-5.txt", "jsonld": "https://wpnews.pro/news/what-s-new-in-claude-sonnet-5.jsonld"}}