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Claude Sonnet 4.5: Anthropic's Advanced Model for Complex Tasks

Claude Sonnet 4.5 is Anthropic's advanced AI model released in late September 2025. It excels at programming tasks across the full software development lifecycle, including planning, bug fixes, maintenance, and complex refactoring.

Claude Sonnet 4.5 also leads in building complex agents and is the best AI model for using computers autonomously, capable of performing real-world computer tasks like browser navigation and spreadsheet management with high accuracy.

Key Features of Claude Sonnet 4.5

Claude Sonnet 4.5 is Anthropic’s most advanced large language model, optimized primarily for coding workflows, real-world agent tasks, and extended autonomous operation. Its key features include:

State-of-the-art performance on coding benchmarks like SWE-bench Verified, excelling in system design, code security, bug fixes, and specification adherence. It can plan and execute complex software projects autonomously over long hours or days.
Enhanced agentic capabilities enable better tool orchestration, speculative parallel execution, and coordination with sub-agents, supporting complex multi-step workflows with improved reliability.
Advanced memory and context management, including awareness of token usage across tool calls, allowing multi-context and long-running workflows.
Exceptional domain knowledge in specialized areas such as finance, cybersecurity, research, and software engineering, enabling precise task execution.
Top performance in computer use tasks like browsing, form filling, error recovery, and spreadsheet management with high accuracy.

Performance Highlights of Claude Sonnet 4.5

Claude Sonnet 4.5's standout claims include strong real-world coding benchmarks, improved long-context handling, and robust tool-use capabilities, with OSWorld and SWE-bench Verified scores highlighting substantial gains over previous Sonnet versions.

The following are the key performance highlights of Claude Sonnet 4.5 (as reported by Anthropic and independent benchmarks):

Coding and software tasks: Claude Sonnet 4.5 shows record or near-record performance on SWE-bench Verified, a benchmark focused on real-world coding tasks. Early reports indicate top-tier results, with some trackers noting high-70s to low-80s under certain configurations. This marks a notable improvement over prior Sonnet generations in sustained, multi-step coding workflows.
Real computer use and task planning: OSWorld benchmarking reports Sonnet 4.5 achieving around 61.4% effectiveness in “real computer use” scenarios, up from 42.2% for Sonnet 4.0, signaling stronger tool use, browser automation, and multi-application planning.
Long-horizon and multi-step tasks: Anecdotal and official notes emphasize improved focus and longevity on complex tasks, including multi-hour sessions, with capabilities for extended reasoning and planning.
Context window and memory: Sonnet 4.5 maintains a large context window (e.g., around the 200K token range) to support long-running tasks, with enhancements in memory management and agent orchestration. This supports more sustained, end-to-end workflows.
Modes and latency: The model supports different modes (default vs. Extended Thinking) that trade latency for deeper reasoning and accuracy. The overall message is that higher-accuracy, longer-horizon work is achievable without prohibitive latency in typical configurations.

How Does Claude Sonnet 4.5 Compare to Other Models

Model	Performance	Speed	Cost	Context Window	Best For	Notes
Claude Sonnet 4.5	Highest (Coding)	Fast	Moderate	1M tokens (API only)	Best coding model, large codebases, complex coding tasks	Strongest for building complex agents, extended autonomous operation, advanced reasoning
Claude Haiku 4.5	Near-Frontier	Fastest (2x Sonnet)	Cheapest	200K tokens	Real-time chatbots, automation, high-frequency tasks	Optimized for speed and scale, less reasoning depth than Sonnet
Claude Opus 4.1	Very High	Slower	Most Expensive	200K tokens	Advanced coding, multi-file refactoring, precise debugging	Highest overall performance but slower, more expensive
Claude Opus 4	High	Slower	Most Expensive	200K tokens	Complex reasoning, architectural decisions	Most expensive model, slower speed
Claude Sonnet 4	Very Good	Fast	Low	200K tokens	High-volume workflows, code reviews, bug fixing, chatbots	Balanced model, efficient for large content generation, supports hybrid reasoning

How to Access Claude Sonnet 4.5

Claude Sonnet 4.5 is accessible through multiple convenient methods, suitable for both everyday users and developers.

The easiest way to access Claude Sonnet 4.5 is on HIX AI. You can try this and other Claude models effortlessly without any restrictions.
Developers can use Claude Sonnet 4.5 through the Claude API by signing up on the Anthropic developer platform, generating an API key from the account settings, and integrating the model using the provided API credentials.

Questions and Answers

What are the key improvements in Sonnet 4.5 compared to earlier versions?

Claude Sonnet 4.5 introduces better code execution, enhanced ability to create complex documents and presentations, deeper strategic thinking, faster multi-tasking output, and improved alignment with user instructions. It also produces cleaner code with fewer errors on the first try.

How large is the context window in Claude Sonnet 4.5?

Claude Sonnet 4.5 supports a large context window of up to 200,000 tokens, enabling it to handle long documents, extended conversations, and complex workflows without losing context.

Does Sonnet 4.5 have a knowledge cutoff date?

Yes, its reliable knowledge cutoff is the end of January 2025. For events or information beyond this date, Claude Sonnet 4.5 uses live web search to provide up-to-date answers when needed.

What is the recommended use case for Claude Sonnet 4.5?

It's recommended for production coding workflows, customer-facing AI agents, real-time research, content generation at scale, and any high-volume or complex AI task requiring advanced capabilities.