Claude Sonnet 4.5
Anthropic's mid-tier AI model released September 2025, optimized for coding and agentic tasks with a 200k token context window.
What is Claude Sonnet 4.5?
Claude Sonnet 4.5 is Anthropic's mid-tier AI model released in September 2025, built specifically for complex coding tasks and autonomous agent work.
It scored 77.2% on the SWE-bench Verified coding benchmark and can maintain focus on multi-step tasks for over 30 hours straight. The model supports a 200k token context window (with a 1M token beta version available).
Most builders use it through the Claude API, Claude.ai, or integrated into tools like Cursor. It's particularly good at understanding large codebases, building multi-file features, and running extended thinking processes where you can watch it reason through problems step-by-step.
Pricing is $3 per million input tokens and $15 per million output tokens. It sits between Claude Haiku 4.5 (faster, cheaper) and Claude Opus 4.5 (most capable, released November 2025).
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Related Terms
AI agents that autonomously plan, write, test, and refactor code with minimal human prompting, handling entire workflows instead of single tasks.
Anthropic's fastest, most affordable AI model that delivers near-frontier coding performance at one-third the cost of premium models.
The amount of text an AI model can remember and process at once, measured in tokens. Bigger windows mean longer conversations and documents.
Reusable instruction packages that teach Claude how to complete specific tasks consistently, loaded dynamically only when needed.
A trained algorithm that takes inputs (text, images, data) and produces outputs (predictions, classifications, generated content).
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