bytecodealliance/wasmtime v50.0.0

on GitHub

50.0.0

Released 2026-10-20.

Added

• Wasmtime now supports the WebAssembly compact imports proposal, disabled by
  default, via Config::wasm_compact_imports.
  #14335

• The Wasmtime CLI now has options to configure unsafe intrinsics and
  compile-time builtins.
  #14279

• The Wasmtime CLI and C API can now enable the component model's canonical
  names and accessors features.
  #14344
  #14497

• A new Store::gc_heap_grow method can be used to manually grow the GC heap
  of a store.
  #14341

• A new ResourceAny::resource_drop_concurrent method can be used to drop a
  guest resource with only an Accessor.
  #14362

• A new Engine::release_idle_pool_memory method can be used to release memory
  kept resident by the pooling allocator for idle slots.
  #14419
  #14507

• A new off-by-default task-group-hook feature enables embedders to associate
  guest-to-host calls with their corresponding host-to-guest calls when using
  component-model-async.
  #14416

• The wasmtime-wasi and wasmtime-wasi-http crates now support "named
  imports", the implements field of the component model.
  #14275

• The wasmtime explore command now supports components and has resizable
  panes.
  #14426
  #14427
  #14458

• The debugger now exposes shared memories to gdbstub.
  #14087

• Winch now supports tail calls on x86_64 and AArch64.
  #14349

• Cranelift has initial support for some x86_64 APX instructions.
  #13916

• The wasmtime serve command can now inherit listening sockets from a service
  manager (e.g. systemd socket units) with a new --systemd-listenfd option,
  can serve on Unix sockets, and can automatically exit when idle with a new
  --idle-process-timeout option.
  #14294
  #14320
  #14392

Changed

• Epoch deadline and call-hook callbacks now receive a StoreHookState
  instead of a StoreContextMut, which only allows access to the T in a
  Store<T>.
  #14386

• The wasmtime CLI no longer enables WASIp0 (wasi_unstable) by default. It
  can be enabled with -Spreview0.
  #14479

• Winch no longer enables the GC types, exceptions, or tail-call proposals by
  default as support for these is not yet Tier 1.
  #14449
  #14502

• Accessor::spawn now takes an async closure instead of an AccessorTask.
  #14376

• Component-model-async has been updated to the latest specification: the
  cancellable immediate has been removed from intrinsics, subtask.cancel
  semantics have been refined, task.cancel now traps before the cancel event
  is delivered, and use of stream/future handles after the other end has been
  dropped now traps.
  #14244
  #14340
  #14342
  #14378
  #14382

• Component-model-async now periodically yields during concurrent work to avoid
  starving other host tasks.
  #14460

• The performance of async guest-to-host calls in component-model-async has
  been improved by lazily creating host tasks, and sync-to-sync adapters no
  longer need to call {enter,exit}-sync-call in many cases.
  #14350
  #14270

• Wasmtime now drops cached compiler contexts between compiling
  modules/components, reducing sustained memory usage.
  #14314

• Cranelift's alias analysis is faster and more precise, and GC struct fields,
  array elements, and GC header fields now all have their own alias regions.
  #14290
  #14425
  #14351
  #14353

• Wasmtime now uses bulk libunwind section registration when available.
  #14304

• Fuel is now charged for more host allocations made with Val.
  #14415

• Default wasi:http hooks now classify connection and TLS errors in more
  detail.
  #14501

• wasi:http now always accepts an empty path-with-query.
  #14446

• The CLI now rejects zero for the --http-outgoing-body-* options.
  #14448

• Work continues on implementing the stack-switching proposal.
  #14140
  #14369
  #14398
  #14441

• Wasmtime now requires Rust 1.97.0 to compile.
  #14466

• The pooling allocator now scans further than a fixed set of region and
  additionally correctly resets pages that have been paged out.
  #14357

Fixed

• Converting a borrowed Resource<T> or ResourceDynamic created with
  new_borrow into a ResourceAny outside of a component call no longer
  panics. The borrow is now lowered into the guest when the call happens, and
  ResourceAny::resource_drop is no longer required for such borrows.
  #14384

• Recursive run_concurrent is now allowed for disparate stores.
  #14302

• Fuel is now correctly saved and restored around call_ref and exception
  catches in Cranelift, and buffered fuel charges in a module's start function
  are no longer dropped.
  #14407
  #14391

• The check-write budget is now enforced in wasi:http outgoing bodies and
  some wasi:io output streams.
  #14408
  #14429
  #14505

• Store::set_epoch_deadline no longer overflows with very large deltas.
  #14513

• JIT code is now made coherent with the instruction cache correctly on
  AArch64.
  #14454

• Native stack-walking on macOS arm64 has been fixed.
  #14303

• A stack overflow translating a variant with a huge number of cases between
  components has been fixed.
  #14355

• Resource aliases are now preserved when stubbing unknown imports.
  #14396

• bindgen! now uses fully-qualified paths for prelude types to avoid
  collisions with WIT type names.
  #14543

• Validation of if without else in the presence of subtyping has been fixed.
  #14334

• A debug assertion in ref.test of internalized externrefs has been fixed.
  #14315

• Cranelift now allows returns via xmm1 with WindowsFastCall for
  extern "Rust".
  #14361

• cranelift-object now sets symbol flags correctly and returns an error,
  instead of panicking, for data objects declared with different TLS values.
  #14519
  #14469

• Winch now handles unreachable try_table, emits fuel updates before throwing
  exceptions, and preserves typed select result types for GC stack maps.
  #14379
  #14297
  #14455

• wasmtime run now honors the --http-outgoing-body-* options.
  #14440

• Graceful shutdown of wasmtime serve has been fixed.
  #14388

• The CLI no longer panics on overflow when deriving the async stack size.
  #14514

• A number of wasi:filesystem fixes: set-times on directory descriptors,
  stat of symlinks with trailing slashes, the stat fast path, datetime
  overflow, and directory entry file types on filesystems without d_type.
  #14420
  #14387
  #14368
  #14403
  #14381

• Accepted TCP sockets now preserve their peer address after a reset.
  #14443

• MACH_RCV_INTERRUPT is no longer used in the macOS mach ports
  implementation.
  #14414

• wasi-http p3: Correctly enforce content-length for response bodies
  #14822

• wasi-http p3: Apply forbidden header check to trailers
  #14823

• wasi-http: Prohibit duplicate content-length headers
  #14824

• Cranelift/aarch64: fix br_tables with very large target count
  #14826

• Centralize type-checks of futures/streams
  #14827