bytecodealliance/wasmtime v43.0.0

on GitHub

43.0.0

Released 2026-03-20.

Added

• Wasmtime now supports the WASIp3 snapshot 0.3.0-rc-2026-03-15.
  #12557

• The number of frames captured in backtrace collection can now be configured.
  #12542

• Wasmtime now supports fine-grained operator cost configuration for when fuel
  is enabled.
  #12541

• Configuring the gc_support option is now possible through the C API.
  #12630

• Configuring the concurrency_support option is now possible through the C
  API.
  #12703

• Debugging-related APIs have been added to access all modules and instances on
  a store.
  #12637

• All store entities now expose a "unique ID" for debugging purposes.
  #12645

• Cranelift's x64 backend now supports the cls instruction for all integer
  types.
  #12644

Changed

• Internal refactoring and support necessary for handling OOM gracefully
  throughout the runtime is proceeding apace. New APIs such as
  FuncType::try_new are available in addition to many internal changes.
  #12530
  #12537
  (... and many more ...)

• Wasmtime's representation of stack frames in the debugging API no longer
  borrows the store itself and is instead represented as a handle.
  #12566

• Wasmtime now unconditionally sets SO_REUSEADDR for guest-bound sockets.
  #12597

• Cranelift now supports more VRegs which means effectively that larger
  functions will be compilable by default rather than returning a "function too
  large" error.
  #12611

• WASIp3 implementations now limit returned memory by default for randomness and
  HTTP headers.
  #12745
  #12761

Fixed

• Running wasmtime wizer over components with modules that contain an
  _initialize function no longer removes the function to preserve the validity
  of the component.
  #12540

• Borrow state for host async tasks is now handled more correctly throughout
  Wasmtime, especially in the face of cancellation.
  #12550

• Bindings generation now accounts for the fact that future and stream are
  not cloneable types.
  #12155

• The impementation of UDP in WASIp2 has had some wakeup-related bugs fixed.
  #12629

• Cancellation of host subtasks for component-model-async has been improved and
  works more reliably.
  #12640

• Subtask management for component-model-async now no longer reparents which
  fixes a number spec-related divergences.
  #12570

• Converting a wasmtime::Error into anyhow::Error and using downcast has
  been fixed.
  #12689

• Async stream/future read/write cancellation has had some corner cases fixed.
  #12704

• Cranelift's timing infrastructure is now more robust in the face of buggy
  system clocks.
  #12709

• The currently running guest task has been corrected in a number of cases
  related to component-model-async and cooperative threading.
  #12718
  #12735
  #12736
  #12737

• An issue of lost wakeups with the WASIp3 stdin implementation has been fixed.
  #12745