Claude Sonnet 4.5 has officially launched worldwide, setting a new standard for AI in coding, agent development, and advanced reasoning. Built by Anthropic, this latest release matches the pricing of its predecessor, Claude Sonnet 4, but offers significant performance gains, upgraded tools, and cutting-edge safety alignment.
Table of Contents
Pricing and Availability
Claude Sonnet 4.5 is now available across platforms:
- Claude.ai on web, iOS, and Android
- Claude Developer Platform
- Amazon Bedrock
- Google Cloud Vertex AI
Pricing remains unchanged:
- $3 per million input tokens
- $15 per million output tokens
- Save up to 90% with prompt caching and 50% with batch processing.
For developers already using Claude Sonnet 4, upgrading is straightforward: simply update the model name to claude-sonnet-4-5-20250929.
Key Upgrades in Claude Sonnet 4.5
1. Claude Code Enhancements
Claude Code is now more powerful than ever:
- Checkpoints: Save progress and instantly roll back.
- Refreshed terminal interface.
- Native VS Code extension.
These updates make coding workflows smoother, more reliable, and ideal for end-to-end software development.
2. New API Features
- Memory Tool (Beta): Store and retrieve knowledge across sessions, enabling effectively unlimited context.
- Context Editing: Automatically clear outdated tool calls, helping agents manage long-running sessions.
- Improved Tool Parameter Handling: Ensures precise formatting for tools like text editors.
- Enhanced Stop Reasons: New signals help developers handle context-window limits more easily.
- Token Count Optimizations: Built-in efficiency improvements at no extra cost.
3. Claude Apps Upgrades
- Code execution and file creation (spreadsheets, slides, documents) are now integrated directly into conversations.
- Claude for Chrome Extension available to Max users, bringing AI into everyday browser workflows.
Performance Benchmarks
Claude Sonnet 4.5 achieves state-of-the-art results across industry benchmarks:
- SWE-bench Verified (real-world coding): 77.2%, making it the world’s best coding model.
- OSWorld (computer use tasks): 61.4%, a massive leap from Sonnet 4’s 42.2% just four months ago.
- Reasoning and Math: Substantial improvements across domains, from financial modeling to STEM analysis.
Real-World Capabilities
- Maintains 30+ hours of focus on complex multi-step tasks.
- Experts in finance, law, medicine, and STEM confirm stronger domain-specific reasoning compared to earlier Claude models, including Opus 4.1.
Use Cases
Claude Sonnet 4.5 powers a wide range of workflows:
- Long-Running Agents: Improved autonomy, tool coordination, and incremental progress tracking.
- Software Development: Handles full lifecycle tasks, from planning to debugging and large-scale refactors.
- Browser and Computer Use: Reliable for tasks like procurement, customer onboarding, and research.
- Cybersecurity: Autonomous vulnerability patching shifts workflows from reactive to proactive defense.
- Financial Analysis: From entry-level insights to predictive analytics and global compliance monitoring.
- Business Productivity: Generate and edit office files with professional polish.
- Research & Content Creation: Synthesizes large datasets, writes nuanced content, and supports creative projects like slides and animations.
Safety and Alignment
Claude Sonnet 4.5 is not only Anthropic’s most capable model but also its most aligned to date:
- Reduced concerning behaviors like sycophancy, deception, power-seeking, and delusional encouragement.
- Major improvements in defending against prompt injection attacks, a critical risk for agentic models.
- Released under AI Safety Level 3 (ASL-3) protections, with safeguards like classifiers to detect dangerous CBRN-related inputs/outputs.
- Misaligned behavior scores are at their lowest yet, as validated by automated auditors and interpretability tests.
Claude Agent SDK
Anthropic has distilled over six months of experience updating Claude Code into the Claude Agent SDK. This SDK provides developers with the same infrastructure that powers Claude’s frontier products, enabling them to:
- Build agents that manage long-running memory.
- Balance autonomy and user control with advanced permission systems.
- Coordinate multiple sub-agents to achieve shared goals.
The SDK is designed not just for coding but for any complex workflow requiring intelligent, autonomous agents.
Research Preview: Imagine with Claude
Alongside Sonnet 4.5, Anthropic is releasing “Imagine with Claude”, a temporary research preview for Max subscribers.
This experiment demonstrates real-time software creation:
- No prewritten code.
- No predetermined functions.
- Claude generates and adapts instantly as you interact.
It’s an exciting glimpse of what’s possible when a powerful model meets the right infrastructure.
Why Upgrade to Claude Sonnet 4.5?
Anthropic recommends all users migrate to Sonnet 4.5 because it is:
- A drop-in replacement for Sonnet 4 with no price increase.
- Vastly more capable in coding, reasoning, and agent development.
- Equipped with better safety, alignment, and memory tools.
Whether you are coding, building agents, conducting financial analysis, or creating content, Claude Sonnet 4.5 offers unmatched performance at the same cost.
Migration Guide
Upgrading from Claude Sonnet 4 to Sonnet 4.5 is simple:
- Update model name to claude-sonnet-4-5-20250929.
- Enable new features like memory tools and context editing for enhanced performance.
- Note: Sonnet 4.5 requires using either temperature or top_p, not both simultaneously.
Final Words
Claude Sonnet 4.5 is Anthropic’s strongest model for coding, agents, and computer use, delivering unmatched benchmark performance, advanced safety measures, and powerful new developer tools. With features like checkpoints, memory management, real-time software generation, and the Claude Agent SDK, it sets a new standard for what AI can achieve in long-running, complex workflows.
At the same price as Sonnet 4, Claude Sonnet 4.5 is the clear choice for developers, enterprises, and professionals seeking the best AI for coding, reasoning, and domain-specific intelligence.
Frequently Asked Questions about Claude Sonnet 4.5
1. What is Claude Sonnet 4.5?
Claude Sonnet 4.5 is the latest large language model from Anthropic’s Claude family. It’s optimized for balance — offering near state-of-the-art reasoning like Claude Opus but at much faster speeds and lower cost. This makes it ideal for research, coding, tutoring, and business use.
2. How is Claude Sonnet 4.5 different from Claude 3.5 Sonnet?
Compared to its predecessor, Claude 3.5 Sonnet, the new version delivers stronger reasoning, more consistent coding capabilities, better comprehension of long or complex queries, and improved alignment with human intent. It also reduces hallucinations and produces more reliable answers.
3. Is Claude Sonnet 4.5 free to use?
Claude Sonnet 4.5 is available on Anthropic’s platform. While there is a free tier with usage limits, full access requires a paid subscription. Some third-party apps and platforms may also integrate Sonnet 4.5 into their services.
4. What can I use Claude Sonnet 4.5 for?
Sonnet 4.5 is versatile — it can draft and edit documents, generate creative text, help with coding tasks, analyze data, tutor in various subjects, and provide professional assistance in research, writing, and customer service. It’s designed for both everyday productivity and advanced workflows.
5. How accurate is Claude Sonnet 4.5?
The model is significantly more reliable than earlier versions, especially in reasoning-heavy tasks, coding, and handling nuanced instructions. While no AI is 100% error-free, Claude Sonnet 4.5 is built to minimize hallucinations and deliver more factual, contextually accurate outputs.
6. Does Claude Sonnet 4.5 support multiple languages?
Yes. Like previous Claude models, Sonnet 4.5 supports multilingual queries and can generate outputs in various languages. However, its strongest performance remains in English.
7. How does Claude Sonnet 4.5 compare to GPT-4 or GPT-5?
Claude Sonnet 4.5 is often faster and more cost-efficient than GPT-4, while maintaining comparable reasoning and creative writing abilities. Against GPT-5, it depends on the use case — GPT-5 may excel in some generative tasks, while Sonnet 4.5 offers better efficiency for balanced workloads.
8. Can businesses integrate Claude Sonnet 4.5 into their apps?
Yes. Anthropic provides API access, allowing businesses to embed Claude Sonnet 4.5 into their products, customer support systems, and workflows. It’s designed for scalability and enterprise-level applications.
