Wasm 3.0 completed — Memory64, multi‑memory, GC, and SpecTec are now official

Key update

WebAssembly 3.0 has been completed and published (finalised Sep 17, 2025). The specification advances the platform in several structural ways that matter for real engineering: a true 64‑bit address space (Memory64), first‑class support for multiple memories per module, a formally specified host garbage collector model (GC) for managed values, new JS string builtins to simplify host‑Wasm string interop, and a new SpecTec toolchain that generates prose, formal semantics and test artifacts from a single source. The announcement notes browser shipping in most major browsers and that standalone engines (e.g., Wasmtime et al.) are on track to add full support. (webassembly.org)

Why it matters

Memory64 removes the old ~4GB ceiling and makes Wasm viable for large in‑memory workloads and data processing tasks that previously required native binaries or complex sharding; expect easier porting of data‑heavy code and fewer workarounds for large datasets. Multi‑memory and the improved text/binary affordances eliminate awkward module‑linking hacks and enable reliable static merging or modular linking of compiled units, which simplifies cross‑language runtimes and static packaging. The host GC and richer reference model are the most consequential change for language portability: they let compilers and toolchains target Wasm while relying on a standard, efficient GC model, which materially lowers the barrier for first‑class support of JVM/CLR/Go‑style managed languages and for richer language runtimes inside Wasm. SpecTec’s machine‑generated prose + formal semantics raises spec reliability and should reduce mismatches between runtimes and tooling, improving test coverage and making regression detection more straightforward. All of these changes are backward compatible, but they do require toolchain and runtime updates; practical next steps for teams are to pin and test on updated runtimes (browsers and Wasm engines), run realistic benchmarks for Memory64/GC paths, and watch for updates to wasm-bindgen, Emscripten, compiler targets and cloud Wasm platforms before migrating production workloads. (webassembly.org)

Source

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