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§3.2 · Chat

claude.ai Project Knowledge — the silent budget killer

Every doc you attach to a Project is sent on every message. Curate ruthlessly.

Claude.ai Projects let you attach reference docs that are included with every message in that project. Convenient — but every doc is sent on every turn, which means a bloated Project Knowledge can quietly add 20,000+ tokens to every single message.

The math

If your Project Knowledge contains a 30,000-token document and you send 50 messages in a month, you've paid for 1.5 million tokens of input just to keep that document attached — whether or not any of those 50 messages actually referenced it.

On Sonnet that's roughly $4.50 of pure overhead. On Opus, $22.50.

The audit

Once a quarter (or after any major document drop), open your Project and run a triage:

  1. What's been attached for >90 days but referenced in <5 messages? Pull it out. Re-attach when you need it.
  2. What's a stale version of a document that has a newer version? Delete the old one. Multiple versions of the same content = double-billing.
  3. What's a 30-page PDF that could be a 1-page summary? Replace with the summary. Re-pull the PDF only when the question requires it.
  4. What's a snapshot of state that's now outdated? Either refresh or remove. Stale facts make Claude wrong in expensive ways.

The Project Knowledge Auditor scores each attached doc on "usefulness ÷ token cost" and ranks them.

Better patterns

  • Use a small instructions block + attach docs only when needed. Most projects don't need a 50k-token brain dump on every message.
  • Save context as @slug references (via the Context Library tool) so you can paste it into a fresh chat when relevant — without paying the per-message tax forever.
  • Start a fresh chat for unrelated work rather than letting one Project accumulate every document for every task you've ever done in it.

What "good" looks like

A well-maintained Project Knowledge is usually under 5,000 tokens of high-signal reference material. If yours is 5× that and you've been using the Project for a year, there's almost certainly low-hanging cleanup worth a real percentage of your monthly bill.