bytecodealliance/wasmtime v49.0.0

on GitHub

49.0.0

Released 2026-09-21.

Added

• Winch now has initial experimental support for the WebAssembly
  exception-handling proposal.
  #14066
  #14081
  #14132
  #14149
  #14180
  #14209

• Wasmtime's type reflection APIs for WebAssembly GC types now have dedicated
  enums for Heap{Top,Bottom}Types.
  #14208

• Wasmtime now supports the use of environment variables to configure most CLI
  arguments in addition to the preexisting CLI flags.
  #14217

• Cranelift will now fold u{add,mul}_overflow results combined with brif
  instructions for more optimal codegen.
  #14217
  #14254

• Components can be tested for equality with a new Component::same API.
  #14257

• The Wasmtime C/C++ API now supports the component-model-implements feature.
  #14264

• Cranelift will now emit the {u,s}bfm instructions on AArch64.
  #14187

Changed

• The wide-arithmetic WebAssembly proposal is now enabled by default.
  #14110

• Config::operator_cost now applies to operators inside constant expressions
  (global initializers, element and data segment offsets, element segment
  expressions) and to the synthesized call to a module's start function.
  Previously each of those was charged 1 fuel unit regardless of the configured
  cost.
  #14215

• Wasmtime's WASI implementation will no longer over-read stdin where possible.
  #14077

• Wasmtime's WASIp2 implementation now maps host-level "broken pipe" errors to
  StreamError::Closed.
  #14107

• Wasmtime's WASIp2 implementation of wasi:http now validates ports in the
  same manner as wasip3.
  #14123

• Wasmtime's WASI implementation of wasi:filesystem now returns the
  is-directory error in some situations when a file is provided.
  #14135

• The wasmtime-wasi-http crate now has the p3 feature enabled by default.
  #14137

• Wasmtime's WASIp2 implementation of wasi:http now runs more hooks from the
  WasiHttpHooks trait in the same manner as wasip3.
  #14167

• Wasmtime now requires Rust 1.96.0 to compile.
  #14184

• Adjustments have been made to the scheduling of threads w.r.t. trapping
  behavior for cooperatively threaded components. These changes are made to
  align with the upstream component-model specification.
  #14146
  #14250

• Fuel for bulk operations is now consumed after the bulk operation has
  completed instead of up-front, restoring previous behavior where a failed very
  large memory growth doesn't trap the original program.
  #14213

• A number of future poll calls throughout the WASIp2 implementation now
  explicitly opt-out of Tokio's per-task cooperative budget to better uphold
  guarantees of WASIp2 APIs.
  #14265

• The run_concurrent function is now allowed to run recursively for separate
  stores, but it still can only be used at most once recursively for any one
  store.
  #14302

• The compile-time performance of the alias analysis in Cranelift has been
  greatly improved.
  #14306