Anthropic Launches Claude Sonnet 4.5 and Introduces Claude Agent SDK

Anthropic has released Claude Sonnet 4.5, saying it outperforms other artificial intelligence models in coding, building complex agents and using computers.

“Claude Sonnet 4.5 is state-of-the-art on the SWE-bench Verified evaluation, which measures complex real-world software coding abilities,” the company said Monday (Sept. 29) in an announcement. “Practically speaking, we’ve observed it maintaining focus for more than 30 hours on complex, multi-step tasks.”

Anthropic added in the post that Sonnet 4.5 leads a benchmark that tests AI models on real-world computer tasks, OSWorld, at 61.4%.

Together with the release of Sonnet 4.5, Anthropic has released upgrades to its products, according to the post.

These include the addition of checkpoints to Claude Code, enabling users to save their progress and roll back to a previous state; the addition of a new context editing feature and memory tool to the Claude API, letting agents run longer and handle greater complexity; and the addition of code execution and file creation directly into the conversation in Claude apps, per the post.

Anthropic also introduced Claude Agent SDK, which gives developers the ability to build AI agents with the same infrastructure that powers its frontier products, the post said.

In addition, the Claude for Chrome extension is now available to Max users who joined the waitlist last month, according to the post.

“We recommend upgrading to Claude Sonnet 4.5 for all uses,” Anthropic said in the post. “Whether you’re using Claude through our apps, our API, or Claude Code, Sonnet 4.5 is a drop-in replacement that provides much improved performance for the same price.”

When Anthropic launched a feature preview on Sept. 9 that allows users of Claude to create and edit files directly within Claude.ai and the desktop app, PYMNTS reported that the move positions the company to more directly compete against OpenAI’s ChatGPT Enterprise, Microsoft Copilot and Google Gemini, which are all pitching AI-driven productivity tools to corporate users.

On Sept. 2, Anthropic said that Claude Code, which was launched fully in May, was generating run-rate revenue of over $500 million. The company also said Anthropic was serving more than 300,000 business accounts.