Wasmtime Files

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