Just to be clear, the audience for that tour is primarily Cloudflare engineers working on workerd / Workers runtime. Within that context, that's very much correct. The entire codebase is written using asynchronous I/O - synchronous I/O doesn't show up (or if it does, it's in weird parts I've never looked). Fibers are used sparingly in very specific contexts and we have very special code to make it memory efficient at our scale.
Just to be clear, the audience for that tour is primarily Cloudflare engineers working on workerd / Workers runtime. Within that context, that's very much correct. The entire codebase is written using asynchronous I/O - synchronous I/O doesn't show up (or if it does, it's in weird parts I've never looked). Fibers are used sparingly in very specific contexts and we have very special code to make it memory efficient at our scale.