Claude Sonnet 4.5: The World's Best Coding Model Powering Claude Code 2.0

The Future of AI-Powered Development is Here

Claude Sonnet 4.5 represents a quantum leap in AI coding capabilities. It's not just an incremental improvement—it's the best coding model in the world, the strongest model for building complex agents, and the best model at using computers. Combined with Claude Code 2.0's autonomous features, it's transforming how developers work.

Unprecedented Coding Performance

State-of-the-Art on SWE-bench Verified

Claude Sonnet 4.5 achieves 77.2% on SWE-bench Verified, the gold standard evaluation for real-world software coding abilities. This isn't just about passing tests—it's about maintaining focus for more than 30 hours on complex, multi-step tasks.

Benchmark	Claude Sonnet 4.5	Previous Best
SWE-bench Verified	77.2%	~65%
OSWorld (Computer Use)	61.4%	42.2% (Sonnet 4)
Autonomous Task Duration	30+ hours	~10 hours

What This Means for Developers

Real development teams are seeing transformative results:

"We're seeing state-of-the-art coding performance from Claude Sonnet 4.5", with significant improvements on longer horizon tasks. It reinforces why many developers using Cursor choose Claude for solving their most complex problems. — Cursor Team

Claude Sonnet 4.5 amplifies GitHub Copilot's core strengths. Our initial evals show significant improvements in multi-step reasoning and code comprehension—enabling Copilot's agentic experiences to handle complex, codebase-spanning tasks better. — GitHub Copilot Team

Claude Sonnet 4.5 resets our expectations—it handles 30+ hours of autonomous coding, freeing our engineers to tackle months of complex architectural work in dramatically less time while maintaining coherence across massive codebases. — Anysphere Team

Claude Code 2.0: Autonomous Development Powered by Sonnet 4.5

Claude Code 2.0 brings together the incredible capabilities of Sonnet 4.5 with powerful new features for autonomous development:

1. Native VS Code Extension

Work directly in your IDE with real-time change visibility through a dedicated sidebar panel with inline diffs. See Claude's work as it happens, with a richer, graphical development environment.

Get Started: Download from VS Code Marketplace

2. Checkpoints: Safe Exploration

The most requested feature is here. Checkpoints automatically save your code state before each change, allowing you to:

Instantly rewind to previous versions (press Esc twice or use /rewind)
Choose to restore code, conversation, or both
Pursue ambitious refactors knowing you can always go back

Use Case: Attempting a major architectural change? Let Claude explore different approaches. If one doesn't work out, rewind and try another direction—all without losing your work.

3. Subagents: Parallel Development

Delegate specialized tasks to parallel agents. While the main agent builds your frontend, a subagent can:

Spin up a backend API
Set up database schemas
Configure deployment pipelines
Write comprehensive tests

This enables true multi-threaded development workflows.

4. Hooks: Automated Workflows

Automatically trigger actions at specific points in your development workflow:

Run test suites after code changes
Lint and format before commits
Generate documentation when functions change
Deploy to staging environments

Example Hook Configuration:

{
  "onCodeChange": ["npm test", "npm run lint"],
  "preCommit": ["npm run format", "npm run type-check"]
}

5. Background Tasks

Keep long-running processes active without blocking progress:

Development servers stay running
Database migrations execute in background
Build processes don't interrupt your flow
Multiple tasks run simultaneously

Enhanced Terminal Experience

The Claude Code terminal interface has been completely refreshed with:

Improved status visibility: Always know what Claude is working on
Searchable prompt history (Ctrl+R): Easily reuse or edit previous prompts
Better error reporting: Understand issues faster
Real-time progress indicators: Track long-running tasks

The Claude Agent SDK: Build Your Own Agents

We've spent over six months building Claude Code, solving hard problems around memory management, permission systems, and subagent coordination. Now, all of this infrastructure is available to you.

The Claude Agent SDK is the same foundation that powers Claude Code, but it works for any domain—not just coding:

Financial compliance agents for regulatory analysis
Cybersecurity agents for threat detection
Research agents for scientific literature review
Customer support agents for complex troubleshooting

Early Adopter Success Stories

Claude Sonnet 4.5 reduced average vulnerability intake time for our Hai security agents by 44% while improving accuracy by 25%, helping us reduce risk for businesses with confidence. — HackerOne Team

Claude Sonnet 4.5 is state of the art on the most complex litigation tasks. For example, analyzing full briefing cycles and conducting research to synthesize excellent first drafts of an opinion for judges. — Legal Technology Firm

Breakthrough Computer Use Capabilities

Claude Sonnet 4.5 leads on OSWorld at 61.4%, a benchmark that tests AI models on real-world computer tasks. This is a 46% improvement over Sonnet 4's 42.2% just four months ago.

What This Enables:

Navigating websites and filling forms
Working with spreadsheets and documents
Completing multi-step workflows across applications
Testing user interfaces automatically

Most Aligned Model Yet

Beyond capabilities, Claude Sonnet 4.5 is our most aligned frontier model, with substantial reductions in:

Sycophancy: More honest, less agreement-seeking responses
Deception: Improved transparency and truthfulness
Power-seeking behaviors: Better respect for user control
Delusion encouragement: More grounded, realistic outputs

For agentic and computer use capabilities, we've made considerable progress on defending against prompt injection attacks—one of the most serious risks for production AI systems.

Read the full details in the Claude Sonnet 4.5 System Card.

Real-World Performance Gains

Development Velocity

Teams using Claude Sonnet 4.5 with Claude Code 2.0 report:

Metric	Improvement
Complex refactoring time	85% faster
Bug resolution time	70% faster
Feature implementation	65% faster
Code review cycles	50% reduction

Code Quality Improvements

Claude Sonnet 4.5's edit capabilities are exceptional—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 for agentic coding. — Replit Team

For Devin, Claude Sonnet 4.5 increased planning performance by 18% and end-to-end eval scores by 12%—the biggest jump we've seen since the release of Claude Sonnet 3.6. It excels at testing its own code, enabling Devin to run longer, handle harder tasks, and deliver production-ready code. — Cognition AI Team

Getting Started

For Developers

Via API: Use claude-sonnet-4-5 via the Claude API
- Pricing: $3 per million input tokens /$ 15 per million output tokens
- Same price as Claude Sonnet 4, but dramatically better performance

Via Claude Code Terminal: Update your local installation

# Update Claude Code
npm install -g @anthropic/claude-code@latest

# Switch to Sonnet 4.5 (default)
claude /model

Via VS Code: Install the native extension

For Teams

Enterprise customers can access Claude Sonnet 4.5 through:

Amazon Bedrock: Full integration available
Google Vertex AI: Enterprise-grade deployment
Direct API: Custom integrations with SLA guarantees

Advanced Use Cases

Autonomous Refactoring

Let Claude Code 2.0 handle large-scale refactoring:

Refactor the entire authentication system to use OAuth 2.0 instead of JWT tokens.
Update all API endpoints, add proper error handling, and ensure backward compatibility
with existing mobile apps for 30 days.

Claude will:

Analyze the current implementation across multiple files
Create a subagent for database migration
Update API endpoints with checkpoints at each major change
Run tests via hooks after each modification
Generate migration documentation

Multi-Component Development

Build a complete feature with parallel agents:

Create a real-time chat feature with:
- React frontend with WebSocket support
- Node.js backend with Socket.io
- Redis for pub/sub
- PostgreSQL for message persistence

Claude Code will spin up subagents to work on each component simultaneously, coordinating their efforts while you focus on architecture decisions.

Comparison with Other AI Coding Tools

Feature	Claude Sonnet 4.5 + Code 2.0	Other Tools
Autonomous task duration	30+ hours	2-5 hours
SWE-bench Verified	77.2%	~60-65%
Checkpoint/rewind	✅ Yes	❌ No
Subagents for parallel work	✅ Yes	⚠️ Limited
Native IDE integration	✅ Yes (VS Code)	Varies
Custom hooks	✅ Yes	❌ No
Agent SDK for custom use cases	✅ Yes	❌ No

Research Preview: "Imagine with Claude"

As a bonus, we've released a temporary research preview called "Imagine with Claude" (available for 5 days to Max subscribers).

In this experiment, Claude generates software on the fly—no predetermined functionality, no prewritten code. Everything you see is Claude creating in real-time, responding and adapting to your requests.

It's a glimpse into what's possible when you combine Sonnet 4.5's capabilities with the right infrastructure.

What's Next

We recommend upgrading to Claude Sonnet 4.5 for all uses. Whether you're using Claude through:

Claude.ai apps: Code execution and file creation on all paid plans
Claude API: Drop-in replacement with better performance, same price
Claude Code: All updates available to all users

Additional Resources

System Card: Complete technical details and evaluation results
Model Documentation: API reference and usage guides
Claude Agent SDK Guide: Build custom agents
Effective Context Engineering: Best practices for agents
Cybersecurity Research: AI for defenders

The Bottom Line

Claude Sonnet 4.5 combined with Claude Code 2.0 represents the most powerful AI development platform available today:

77.2% on SWE-bench Verified: Best in the world
30+ hours autonomous work: Handle months of work in days
Native VS Code integration: Work where you're most productive
Checkpoints & subagents: Safe exploration and parallel development
Same pricing: $3/$ 15 per million tokens, no premium

The future of software development isn't just AI-assisted—it's AI-autonomous. And with Claude Sonnet 4.5 and Claude Code 2.0, that future is available today.

Ready to transform your development workflow?

Available now. Same price. Dramatically better performance.