Wasmtime Files

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