Anthropic · Claude Sonnet line · lightweight
Claude Sonnet 4.5 was released by Anthropic on September 29, 2025, as a lightweight model in the Claude Sonnet line.
Claude Sonnet 4.5 completes 61.4% of OSWorld computer tasks, up from 42.2% for Claude Sonnet 4, at the same $3 / $15 price per 1M tokens.
Compared with Claude Sonnet 4 · the model it replaces
Fixes more than 3 in 4 real software bugs
SWE-bench Verified — fixing real bugs in real software projects
77.2%
▲ up from 72.7% · +4.5 points · Sonnet 4.5 with a 200K thinking budget and a short extra prompt, Sonnet 4 without extended thinking
Costs the same as the model it replaces
Price per 1M tokens — what developers pay, input / output
$3 / $15
same as Claude Sonnet 4
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Claude Sonnet 5.5 is the current model in this line. The card shows how long it has been since the last release against the line's usual gap and its recent ones — the rhythm, not a date.
Latest: Claude Sonnet 5.5 · Sep 28, 2026
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