What’s New in WebAssembly 3.0? Exploring the Latest Features and Their Impact

WebAssembly (Wasm) standard 3.0 is now completed and is regarded as the “live” standard.

This release comes three years after Wasm 2.0, which added many features such as vector instructions, bulk memory operations, multiple return values, and simple reference types.

Compared with version 2.0, this is a major update; several of the available features have been under development for six to eight years.

Key Features of Wasm 3.0

64‑bit address space – memory and tables can use i64 as address space, expanding the theoretical address space from 4 GB to 16 EB. In practice, hardware and use‑cases become limiting factors, e.g., the Web caps 64‑bit memory at 15 GB.

https://github.com/WebAssembly/spec/blob/wasm-3.0/proposals/memory64/Overview.md

Support for multiple memories within a single module, whereas previously multiple memory objects could only be declared and accessed across separate modules.

https://github.com/WebAssembly/spec/blob/wasm-3.0/proposals/multi-memory/Overview.md

Garbage collection (GC) – low‑level integration that lets compilers declare the memory layout of runtime data structures as structs, arrays, and unboxed tagged integers, with allocation and lifetime managed by Wasm; other responsibilities remain with the compiler.

https://github.com/WebAssembly/spec/blob/wasm-3.0/proposals/gc/Overview.md

Function references – richer reference forms that describe the exact shape of heap values.

https://github.com/WebAssembly/spec/blob/wasm-3.0/proposals/function-references/Overview.md

Tooling and developer convenience improvements: the text format now supports custom comment syntax for additional information without affecting semantics, and a built‑in JavaScript API for string handling reduces cross‑environment conversion costs. This 3.0 spec is the first produced with the SpecTec toolchain, improving consistency and reliability.

Other new features include:

Tail calls – https://github.com/WebAssembly/spec/blob/wasm-3.0/proposals/tail-call/Overview.md

Exception handling – https://github.com/WebAssembly/spec/blob/wasm-3.0/proposals/exception-handling/Exceptions.md

Relaxed SIMD – https://github.com/WebAssembly/spec/blob/wasm-3.0/proposals/relaxed-simd/Overview.md

Deterministic defaults for instructions with nondeterministic results – https://github.com/WebAssembly/profiles/blob/main/proposals/profiles/Overview.md

These new capabilities provide better support for compiling high‑level programming languages to Wasm. Several major languages, including Java, OCaml, Scala, Kotlin, Scheme, and Dart, are already targeting Wasm.

Wasm 3.0 features have been incorporated into most mainstream browsers—Chrome, Firefox, and Safari—and the standalone engine Wasmtime is also nearing full compatibility.