Anthropic's API finally added support for being directly used from the browser!
I filed a bug asking for this earlier this year: https://github.com/anthropics/anthropic-sdk-typescript/issues/248 to enable https://github.com/jkomoros/code-sprouts.
This allows an architecture where the webapp is statically served from a domain and the user configures it by putting in their LLM API keys.
The webapp never sees any of the user's data; the webapp is entirely static.
The user pays for their own LLM use.
A very different kind of architecture!