Introducing Claude Sonnet 4.5

Summary

The release introduces Claude Sonnet 4.5 as a model aimed at complex coding, agentic work, computer use, reasoning, and math, with claimed gains in alignment. It reports state-of-the-art SWE-bench Verified performance and a 61.4% OSWorld score, up from Sonnet 4’s 42.2%, while noting more than 30 hours of observed focus on complex multi-step tasks. Alongside the model, the company released Claude Agent SDK, added Claude Code checkpoints, a refreshed terminal interface, native VS Code extension, context editing, and a memory tool, and brought code execution and file creation to paid Claude apps. Sonnet 4.5 is available through the Claude API as claude-sonnet-4-5 at $3/$15 per million tokens, the same pricing as Sonnet 4. It is released under AI Safety Level 3 protections, with reported reductions in concerning behaviors and improved defenses against prompt injection, while the temporary Imagine with Claude preview is available to Max subscribers for five days.

Takeaways

1. 1

   Claude Sonnet 4.5 reports a 61.4% OSWorld score, compared with 42.2% for Sonnet 4 four months earlier, and more than 30 hours of observed focus on complex multi-step tasks.

2. 2

   The Claude Agent SDK exposes the infrastructure used by Claude Code for building agents beyond coding, including solutions for memory, permission systems, and coordinating subagents.

3. 3

   Claude Sonnet 4.5 keeps Sonnet 4 pricing at $3/$15 per million tokens and is released under AI Safety Level 3 protections with defenses against prompt injection and classifiers for CBRN-related content.