Anthropic LLM Medium Closed weights

Claude Sonnet 4.5

409 days since Anthropic announced it · 29 Sep 2025

Claude Sonnet 4.5 is a closed-weights LLM from Anthropic, announced 29 Sep 2025. It costs $3 per 1M input tokens and $15 per 1M output tokens. Its context window is 200K tokens.

Input: $3; per 1M tokens
Cache write: $3.75; per 1M tokens
Cache read: $0.30; per 1M tokens
Output: $15; per 1M tokens
Context window: 200K; tokens
Parameters: —; not disclosed

Announcement: anthropic.com/news/claude-sonnet-4-5
Docs: platform.claude.com/docs/en/models/sonnet-4-5/overview

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Anthropic · Medium

closed weights

Claude Sonnet 5.5 +90d 28 Sep 2026
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Claude Sonnet 4.5 29 Sep 2025