AIster · The agentic age · Launches
Anthropic releases Claude Sonnet 4.5
A model built for long agent tasks, with the toolkit behind Claude Code
Key facts
- Date
- 29 Sep 2025
- Era
- The agentic age
- Interest
- Launches
- Threads
- Model wars, Agents
- Released
- 29 Sep 2025; 77.2% SWE-bench Verified; 61.4% OSWorld; $3/$15 per million tokens
- Also launched
- Claude Agent SDK, Claude Code checkpoints and a native VS Code extension
Claude Sonnet 4.5 arrived on 29 September 2025, scoring 77.2% on SWE-bench Verified (a test built from real software bugs) and, Anthropic said, able to stay focused on complex tasks for more than 30 hours. Alongside it came the Claude Agent SDK, the infrastructure behind Claude Code, so developers could build their own agents (AI systems that carry out multi-step tasks on their own).
Sources
- Anthropic, Introducing Claude Sonnet 4.5, 2025-09-29