Claude Sonnet 4.5 is a large-context AI model introduced in September 2025. With a context window up to 1 million tokens (beta) and improvements to coding, reasoning, memory management, and tool use, Sonnet 4.5 is especially suited for software development and autonomous agents.
The model is accessible through multiple channels—including IDE integrations, APIs, and web/mobile apps. This guide explores every possible way to use Claude Sonnet 4.5 and highlights free or trial options.