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WASI preview 3 was stabilized in late 2025 and adds what preview 2 lacked: native async, bidirectional streams, and inter-component concurrency with specified semantics. Portability and async are no longer a trade-off, since one async component runs unchanged on wasmtime, WasmEdge, JCO and the main commercial runtimes. API gateways and SaaS extension plugins are the strongest production cases.
containerd Wasm support is production ready: the runwasi shim ships in containerd 2.0 and is backported to 1.7.7 and 1.6.25, so WasmEdge or wasmtime workloads run beside ordinary Linux containers on one Kubernetes cluster, selected per pod through RuntimeClass. Wasm wins on cold start, image size and kernel-free sandboxing, but not every workload fits.
WASI 0.3, also known as preview 3, was ratified on June 11, 2026, adding native asynchronous concurrency to the WebAssembly component model through streams, futures, and async functions. It fixes old fragmentation across languages and runtimes, enables real composition between Wasm services, and paves the way for cooperative threads planned in upcoming 0.3.x releases.
WASI 0.2 reached GA in January 2024, bringing WebAssembly's Component Model into production: typed WIT interfaces that let Rust, Go, and JavaScript code compose without manual glue code. That shift makes edge functions with sub-1 ms cold start, secure plugins, and untrusted-code sandboxing viable today, though it does not replace containers for traditional apps.
Fastly Compute runs WebAssembly code on its ~70 global PoPs with a 35-microsecond cold start. Supports Rust, Go, and JavaScript compiled via Javy. Competes directly with Cloudflare Workers, with advantages for compute-intensive workloads and teams already on Fastly CDN, but at a higher entry cost.
WASI Preview 2 redefines how WebAssembly interacts with the operating system. It introduces the Component Model with typed WIT interfaces and granular capabilities, enabling modules written in different languages to compose without manual serialisation. The full standard arrives in 2024 with direct impact on edge functions, plugins, and serverless.
WebAssembly is moving beyond the browser through WASI, the standard system interface, and the component model, which defines declarative WIT interfaces so modules written in different languages can compose with each other. Cold start lands around 1 ms versus roughly 500 ms for a container, a key difference for serverless and edge computing teams.
