tl;dr: WASI 0.3 has been ratified, moving async primitives (stream<T>, future<T>, async functions) into the WebAssembly Component Model's canonical ABI, eliminating the per-component event loops and the awkward start/finish/subscribe patterns of 0.2. The host now drives a single shared event loop with completion-based scheduling, enabling idiomatic async bindings across languages (Rust, Go, JS, Python, C#) and allowing direct composition of components—e.g., wasi:http's new middleware world supports service chaining that collapses microservice calls from milliseconds to nanoseconds. Wasmtime 45 runs it now, with 46 enabling it by default.