What's the difference between Claude Sonnet 4 and Sonnet 3.7?

Anthropic ships Sonnet versions roughly every 4-8 months. The lineage today on AskAI.free:

• Sonnet 3.5: June 2024. Available on the free tier. Still very capable for everyday writing.
• Sonnet 3.7: early 2025. Better instruction-following and faster than 3.5. Roughly half the token cost of Sonnet 4.
• Sonnet 4: Anthropic's flagship Sonnet. Strongest at long-form writing, complex reasoning, multi-file code. Costs 4× more tokens per question.

Practical advice: use 3.7 as your daily driver and reach for Sonnet 4 when you have a hard, important task that's worth a few extra cents.

What stays the same across all three: every Sonnet version has a 200,000-token context window, roughly 150,000 words, so document capacity is not a reason to upgrade. The differences show up in output quality. Sonnet 4 follows multi-part instructions more faithfully, drifts off-topic less in long pieces, and produces noticeably stronger code on multi-file problems.

The cost difference matters on paid plans because usage is metered in tokens: the same 2,000-word draft consumes about four times more of your monthly allowance on Sonnet 4 than on 3.7. Concretely, that means a Pro subscriber can run hundreds of everyday 3.7 conversations a month, or a smaller number of heavyweight Sonnet 4 sessions, and most people land on a mix. A sensible split is 3.7 for emails, summaries and quick code, Sonnet 4 for client deliverables, long essays and anything you'll publish under your own name.