Major Improvements Over Claude Sonnet 4

1. Exceptional Coding Capabilities

One of the standout features of Claude Sonnet 4.5 is its coding excellence. It has achieved state-of-the-art performance in coding benchmarks, and it has become the go-to model for developers working on complex coding projects. Here’s what sets it apart:

• SWE-bench Verified Performance: With advanced performance on coding benchmarks, Claude Sonnet 4.5 is now regarded as one of the most reliable AI models for development tasks.

• Better Planning and System Design: The model’s ability to make better architectural decisions and organize code more efficiently makes it an invaluable tool for developers tackling large, intricate projects.

• Enhanced Security Engineering: Claude Sonnet 4.5 excels at identifying security vulnerabilities, making it perfect for creating secure systems and applications.

• Improved Instruction Following: The model can now follow coding specifications with greater accuracy, ensuring that development tasks are executed as per the requirements without unnecessary deviations.

2. Autonomous Agent Capabilities

While previous iterations of Claude Sonnet were already impressive in terms of autonomy, the 4.5 version takes it to the next level. Extended autonomous operation is now possible, allowing agents to function independently for hours while maintaining focus on incremental tasks. This is ideal for scenarios requiring long-running tasks where continuous agent operation is needed.

• Task Incrementalism: Rather than attempting everything at once, Claude Sonnet 4.5 makes steady progress on a few tasks at a time, ensuring a more manageable and logical approach to complex projects.

• Fact-Based Progress Updates: Agents can now provide factual progress updates that accurately reflect what has been accomplished so far, offering a reliable status report for ongoing projects.

3. Context Awareness and Management

Claude Sonnet 4.5’s context awareness ensures the model tracks its token usage across conversations. This feature is especially useful for long-running tasks as it helps the model avoid premature task abandonment. By understanding the context in which it is working, Claude Sonnet 4.5 can better coordinate and execute tasks across multiple sessions.

• Extended Context Handling: The model can effectively maintain coherence over extended periods, which is especially beneficial for tasks like research and coding where context retention is critical.

• Improved Tool Usage: Claude Sonnet 4.5 leverages parallel tool calls, meaning it can perform multiple speculative searches or read several files simultaneously to build context faster.

4. Creative Content Generation

Claude Sonnet 4.5 is not just about coding and agents—it also excels at creative content generation. Whether you’re building a presentation, creating animations, or generating blog posts, Claude Sonnet 4.5 produces polished, professional results in a fraction of the time.

• First-Try Quality: The model produces well-designed and usable creative content even on the first attempt.

• Slide and Visual Content Creation: When compared to other models like Claude Opus 4.1, Claude Sonnet 4.5 surpasses expectations in producing polished slides and visual content.

Key Features of Claude Sonnet 4.5

1. Memory Tool (Beta)

Claude Sonnet 4.5 introduces a memory tool that allows the model to store and retrieve information beyond the context window. This new feature is invaluable for building knowledge bases, maintaining project states, and preserving context over multiple sessions. Whether you’re working on a long-term research project or a complex coding workflow, this tool ensures no information is lost.

2. Context Editing for Improved Management

The context editing feature in Claude Sonnet 4.5 helps manage large volumes of data by automatically clearing older tool calls as the context window approaches its limit. This allows users to maintain clarity and coherence even during long-running tasks, enhancing overall efficiency.

3. Enhanced Stop Reasons

Claude Sonnet 4.5 now includes a new stop reason called “model_context_window_exceeded”, which indicates when the model’s generation stops due to hitting the context window limit. This makes it easier to handle context window limitations and improve session management.

4. Tool Parameter Handling Improvements

Claude Sonnet 4.5 fixes a bug related to trailing newlines in string parameters passed to tools. Previously, trailing newlines were stripped, but now they are preserved, ensuring precise formatting in tools that require it.

Pricing and Availability

Claude Sonnet 4.5 maintains the same pricing structure as the previous version:

• Input: $3 per million tokens

• Output: $15 per million tokens

The model is available on various platforms, including:

• Claude API: claude-sonnet-4-5-20250929

• Amazon Bedrock: anthropic.claude-sonnet-4-5-20250929-v1:0

• Google Cloud Vertex AI: claude-sonnet-4-5@20250929

It is also accessible through Claude.ai and Claude Code platforms.

FAQs About Claude Sonnet 4.5

1. What makes Claude Sonnet 4.5 different from Claude Sonnet 4?
   Claude Sonnet 4.5 features enhanced coding capabilities, autonomous agent operations, and context management, making it more efficient for long-running tasks like research and financial analysis.

2. How does Claude Sonnet 4.5 improve security engineering?
   The model includes more robust security practices and vulnerability detection, which makes it ideal for secure system design and building applications with enhanced security features.

3. What is the Memory Tool in Claude Sonnet 4.5?
   The Memory Tool allows the model to store information outside of its context window, preserving project state and building knowledge bases over time for extended tasks.

4. Can Claude Sonnet 4.5 handle creative content generation?
   Yes, Claude Sonnet 4.5 excels at creating polished content like presentations, animations, and more, with first-try quality and professional output.

5. What is the pricing structure for Claude Sonnet 4.5?
   Claude Sonnet 4.5 is priced at $3 per million tokens for input and $15 per million tokens for output, making it affordable for a wide range of applications.