Claude context window calculator
Plan how much room your Claude context bundle needs before you upload files or paste a large source package.
Claude Fable 5.1 budget planner
Claude Fable 5.1 supports a 1M-token context window and up to 128K output tokens. Anthropic's highest-capability model, built for demanding reasoning and long-horizon agentic work.
Estimated cost
Source: Anthropic documentation. Last reviewed 2026-09-08. Prices reviewed 2026-09-08.
Frequently asked questions
What context windows does this calculator use for Claude?
It shows all four current Claude variants: Fable 5.1 (1M tokens), Opus 5 (1M tokens), Sonnet 5 (1M tokens), and Haiku 4.5 (200K tokens). Select any variant to plan your budget.
Should I fill the whole Claude context window?
Usually no. Reserve room for your instructions and the response. A focused 60K-token bundle can outperform a noisy 900K-token dump.
Can Riflet build the source context?
Yes. Riflet can combine folders, PDFs, websites, GitHub repos, Obsidian vaults, and Notion exports into a portable context file for Claude.
Does Riflet update Claude Projects automatically?
No. Riflet exports the file. You choose when to upload or replace it in Claude.