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Claude Sonnet 4.5 — A New Era in AI Development

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Anthropic has released Claude Sonnet 4.5, and this isn't just another update. This is the world's best coding model, a game-changer for building AI agents and automating complex tasks.

What Can the New Model Do?

Next-level coding. Claude Sonnet 4.5 shows incredible results on SWE-bench Verified—a benchmark that tests real-world coding abilities. The model can focus on complex, multi-step tasks for over 30 hours straight, maintaining context and logic throughout.

Computer use mastery. On OSWorld, a benchmark that tests AI's ability to perform real computer tasks, the new model hit 61.4%. For comparison: just four months ago, Claude Sonnet 4 scored 42.2%. That's a massive leap!

Enhanced reasoning and math. The model demonstrates significant progress in logic, mathematical problems, and reasoning. Experts in finance, law, medicine, and STEM fields note dramatically improved knowledge and analytical capabilities compared to previous versions.

Product Updates

Along with the model, some killer ecosystem updates dropped:

Claude Code got checkpoints—one of the most anticipated features. Now you can save progress and roll back to previous states instantly. The terminal interface has been refreshed and a native VS Code extension is here.

Claude API now supports context editing and a memory tool, allowing agents to run even longer and handle more complex tasks.

Claude apps (web, mobile, desktop) now have code execution directly in conversations and file creation—spreadsheets, presentations, and documents.

Claude for Chrome extension is now available to Max subscribers who were on the waitlist.

Claude Agent SDK

Anthropic is sharing the infrastructure they used to build Claude Code. The new Claude Agent SDK gives you the same tools Anthropic's developers use. Now anyone can build advanced AI agents for their own needs.

The SDK solves hard problems: memory management in long-running tasks, permission systems that balance autonomy with user control, and coordination of sub-agents working toward a common goal.

Safety and Alignment

Claude Sonnet 4.5 is Anthropic's most aligned frontier model yet. Problematic behaviors have been significantly reduced: sycophancy, deception, power-seeking, and encouraging delusional thinking. Protection against prompt injection attacks—one of the biggest threats for agents—has been seriously improved.

The model is released with ASL-3 level protections, including classifiers to detect potentially dangerous content, especially related to CBRN (chemical, biological, radiological, and nuclear) weapons.

Imagine with Claude — Bonus Feature

There's a five-day research preview of "Imagine with Claude" available to Max subscribers. Claude generates software on the fly, with no pre-written code. Everything is created in real-time in response to your requests.

How to Get Started?

Claude Sonnet 4.5 is available everywhere right now:

  • For developers: use claude-sonnet-4-5 via Claude API
  • Pricing: same as Claude Sonnet 4 — $3/$15 per million tokens
  • For everyone: available in web app, mobile, and desktop versions

Expand Your Capabilities with MCP

Want even more from Claude? At fastmcp.me you'll find tons of useful MCP (Model Context Protocol) servers that work with Claude, Claude Desktop, and Claude Code. These are ready-to-use tools for integrating Claude with your favorite services and workflows.

Early User Feedback

Real companies are already using the new model and sharing their experiences:

Cursor: "We're seeing state-of-the-art coding performance with significant improvements on longer horizon tasks."

GitHub: "Claude Sonnet 4.5 amplifies Copilot's core strengths. Our initial evals show significant improvements in multi-step reasoning."

HackerOne: "Reduced average vulnerability intake time by 44% while improving accuracy by 25%."

Replit: "We went from 9% error rate on Sonnet 4 to 0% on our internal code editing benchmark. Higher tool success at lower cost is a major leap."

Canva: "Impressive gains on our most complex, long-context tasks. It's noticeably more intelligent and a big leap forward."

Claude Sonnet 4.5 isn't just an improvement. It's a new standard for AI models that actually help with real work. Upgrading to Sonnet 4.5 is recommended for all use cases—it's a drop-in replacement for previous versions with much better performance at the same price.