Anthropic: Claude Sonnet 4.5 API Price, Cost Calculator & Specs

Claude Sonnet 4.5's real advantage isn't intelligence—it's context window math. For $3/1M input tokens and $15/1M output tokens, you get 1 million tokens of context at roughly the same price point as competitors offering 200K-400K contexts. That's 2.5-5x more processing power per dollar for long-form tasks.

The 1M context changes everything for specific use cases. Document analysis, codebases with thousands of files, multi-session agent workflows—these are scenarios where smaller context windows force expensive chunking and retrieval strategies. Sonnet 4.5 lets you feed entire documentation sets, legal contracts, or research papers without architectural gymnastics.

Compared to Opus 4.5's $5/$25 pricing with only 200K context, Sonnet 4.5 offers 5x the context at 60% the input cost and 60% the output cost. The performance difference might not justify Opus 4.5's 67% price premium for most practical applications.

When Sonnet 4.5 Makes Sense:

Document Processing Pipelines: Legal firms analyzing contracts, consulting companies processing research reports, or compliance teams reviewing policies. The 1M context window eliminates the need for expensive document chunking strategies.

Codebase Intelligence: IDE plugins, code review tools, or refactoring assistants that need to understand large codebases without losing context across multiple files and modules. This is where the 1M context genuinely outperforms smaller alternatives.

Long-Running Agent Workflows: Research agents, financial analysis systems, or planning tools that maintain state across extended interactions. The enhanced context tracking prevents the "memory loss" problem that plagues smaller context windows.