Claude Sonnet 4.5

Previous-generation Sonnet with a 200K context window.

API model ID	`claude-sonnet-4-5-20250929`
Context window	200K tokens
Max output	64K tokens
Input price	$3 per million tokens
Output price	$15 per million tokens
Knowledge cutoff	Jan 2025
Released	Sep 29, 2025
Tokenizer generation	Classic (Sonnet 4.6 and earlier)
Status	Active

From the announcement

Hit 77.2% on SWE-bench Verified.
Observed holding focus for more than 30 hours on multi-step tasks.
The Claude Agent SDK shipped alongside it.

Read Anthropic's announcement

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