PSA for anyone using Claude projects to compartmentalize their work: check your project settings right now.

Anthropic quietly introduced a “Use account memory” toggle inside each project. When I discovered it tonight, it was already enabled on every existing project in my account. It bridges your project’s memory with your account-level memory — the pool that loads into every regular conversation you have.

If you set up a project specifically for isolation — client work, sensitive research, creative work you don’t want bleeding into your professional conversations — that wall has a hole in it, and you were never told.

And this wasn’t a theoretical concern. I already had cross-contamination in my account memory and spent about an hour cleaning it up. I run two projects: one for serious documentation work and another for creative writing. I also use Claude for job-search work, including checking resume updates for errors or inconsistencies, reviewing professional writing, and strategy planning. Material from those contexts had ended up mixed together in account memory. Character names from stories were sitting alongside my real career history. Serious research was adjacent to parody.

Here’s what makes this worse:

Anthropic’s own help center documentation, as of tonight, still describes project memory as isolated: “Each project has its own separate memory space and dedicated project summary, so the context within each of your projects is focused, relevant, and separate from other projects or non-project chats.”

That is no longer true by default.

The toggle appears to have arrived with the September 16-17 platform unification — when Cowork merged into Chat and Projects were redesigned. There was no announcement. No migration notice. No email. No banner. The documentation wasn’t updated. It was just switched on.

(paragraph with use cases removed because it was clearly a distraction from the point)

This needed to be opt-in. Defaulting it to on, silently, on existing projects, while the documentation still promises isolation, is not a minor UX oversight. It’s a breach of the contract the feature was sold on.

I’ve submitted formal feedback. I’d encourage anyone affected to do the same (link in the comments).

edit: relates to WebUI/Chat.