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).
Good to Know
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Related Terms
The text instruction you give an AI model to tell it what you want it to do, like asking ChatGPT to write code or explain a concept.
Reusable instruction packages that teach Claude how to complete specific tasks consistently, loaded dynamically only when needed.
Anthropic's command-line AI assistant that lives in your terminal, reads your codebase, and writes code across multiple files.
The practice of crafting specific instructions to get better outputs from AI models like ChatGPT, Claude, or Gemini.
Anthropic's most capable AI model, built for complex coding, autonomous agents, and multi-step reasoning tasks.
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