49.0.1

Released 2026-09-24.

Fixed

• Do not drop fuel-spend accrued by callees of call_ref and callees that
  return via exception throws.
  GHSA-m63x-6p34-q65x

• Fix fuel spend for dynamic record lifting.
  GHSA-jqpg-j7w6-42pr

• Fix host memory exhaustion on outgoing HTTP body write.
  GHSA-c9gc-w9vx-w86p

• wasmtime-wasi: Fix panic on out-of-range datetimes in WASI filesystem set-times, set-times-at.
  GHSA-j2g9-4prp-pf6h

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

49.0.0

Unreleased.

Added

Changed

• 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

48.0.5

Released 2026-10-02.

Fixed

• Fixed an issue where artifacts for 48.0.4 didn't get correctly published from
  CI and a GitHub release for 48.0.4 wasn't made.
  #14494

48.0.4

Released 2026-10-02.

Fixed

• WASI preview 0 implementation of poll_oneoff circumvents fuel consumption.
  GHSA-j366-h8gg-77pm

• Excessive allocated memory on the host when guests don't have stdio.
  GHSA-gqmc-89g8-p25r

• fd_readdir copies uninitialized struct padding into guest memory.
  GHSA-96f6-r43r-8c24

• Guest can panic host through filesystem timestamp before the epoch on wasip3.
  GHSA-mr2v-56j5-cmfc

• Wasmtime component async-lifted callback result count is unvalidated, causing a native stack buffer overflow.
  GHSA-32h6-97mm-8q3c

• Mis-typed WebAssembly tag imports can lead to GC heap corruption.
  GHSA-cfhf-m2cr-62wj

• Wasmtime wasi:http implementation panics with a zero timeout supplied.
  GHSA-w4qr-p94g-mjhv

• Rooting for GC values live across try_call may be missing, causing GC heap corruption.
  GHSA-hw8m-q44c-ggrf

[automatically-tag-and-release-this-commit]

Co-authored-by: Wasmtime Publish wasmtime-publish@users.noreply.github.com

48.0.3

Released 2026-09-24.

Fixed

• Do not drop fuel-spend accrued by callees of call_ref and callees that
  return via exception throws.
  GHSA-m63x-6p34-q65x

• Fix fuel spend for dynamic record lifting.
  GHSA-jqpg-j7w6-42pr

• Fix host memory exhaustion on outgoing HTTP body write.
  GHSA-c9gc-w9vx-w86p

• wasmtime-wasi: Fix panic on out-of-range datetimes in WASI filesystem set-times, set-times-at.
  GHSA-j2g9-4prp-pf6h

48.0.2

Released 2026-09-10.

Changed

• Wasmtime's dependency on cap-primitives is now vendored within Wasmtime
  itself.
  #14225

Fixed

• Code generated by bindgen! is now compatible with the latest Rust nightly by
  default.
  #14307

48.0.1

Released 2026-08-24.

Fixed

• Context slots in component compositions are now correctly managed.
  #14139

• The Host header is now set by default for HTTP requests sent with WASIp2.
  #14167

48.0.0

Released 2026-08-20.

Added

• Wasmtime has an initial implementation of the component model
  fixed-length-lists feature.
  #12315

• Wasmtime's reflection of component imports/exports now exposes external-id
  information.
  #13874

• Cranelift's alias analysis pass now eliminates dead stores.
  #13806
  #13947

• Winch now supports the wasm SIMD proposal on AArch64.
  #13911
  #13921
  #13928
  #13937
  #13945
  #13938
  #13946
  ...

• Cranelift now supports an AVX512-VNNI lowering for the dot-product wasm
  instruction and usdot on AArch64.
  #14006
  #14054

• Wasmtime's bindgen! macro now has an include_component_type option to
  generate a COMPONENT_TYPE constant with the encoded type of the world being
  bound.
  #14013

• Wasmtime now supports configurable fuel costs for variable-length wasm
  opcodes.
  #13931

Changed

• Host-implemented traits in wasmtime-wasi-http are now the same across
  wasip2/wasip3 and no longer require separate implementations/structures.
  #13810
  #13812
  #13835

• Wasmtime will now use the process_madvise syscall on Linux where available
  which can improve the performance of the pooling allocator when the
  deallocation batch size is configured to larger than 1.
  #13830

• Synchronous cancellation of streams/futures/subtasks now traps if the waitable
  was already in a waitable set.
  #13708

• Winch is now flagged to be compatible with component-model-async.
  #13845

• Wasmtime's pooling allocator now uses more sharding to reduce lock contention.
  #13840

• Wasmtime now requires Rust 1.95.0 to build.
  #13853

• Cranelift now has a uniform maximum size across all backends on the bounds of
  a function's stack frame.
  #13783

• Wasmtime's LinkerInstance for components now supports being reopened to
  gradually add more items.
  #13908

• The wasmtime-wasi crate's default configuration now denies creation of
  TCP/UDP sockets by default.
  #13936

• Wasmtime now configures async task context fields on realloc calls to zero.
  #13949

• Work has continued on continuous verification of Cranelift's lowering rules
  on AArch64.
  #13935
  #13929
  #13998

• Codegen for loads on AArch64 has been optimized slightly to improve sharing
  common sub-expressions.
  #13766

• Work continues on implementing the stack-switching proposal.
  #11717
  #13996
  #14052

• Permissions for wasi-filesystem in the implementation of the wasmtime-wasi
  crate have been simplified to either read-write or read-only for a directory.
  #14010

Fixed

• A late-drop of host-defined stream producers/consumers has been fixed.
  #13891

• Call hooks are now invoked around async yields when dealing with concurrent
  execution.
  #13871

• Extreme filesystem timestamps no longer cause panics.
  #13894

• An erroneous trap was fixed where an async-delivered write-closed event was
  sent to a future.
  #13914

• An erroneous trap where Wasmtime internally used the wrong thread id has been
  fixed.
  #13926

• Cross-component instance streams are no longer erroneously flagged as being
  intra-instance.
  #14018

• A panic in the wasmtime CLI with non-utf8 environment variables has been
  fixed.
  #14017

• Atomic waits on big-endian hosts have been fixed.
  #14027

• Enabling MPK with CoW images has been fixed.
  #14076

47.0.4

Released 2026-08-20

Fixed

• Guest controlled-size host heap allocation through WASIp3 streams.
  GHSA-x84v-gj2h-g759

• Filesystem sandbox escape when paths or symlinks contain trailing slashes.
  GHSA-vqjp-4c8c-hfgg

47.0.3

Released 2026-07-31.

Fixed

• Stores can mix up type indices between engines.
  GHSA-hgjw-h833-99q9

• Preemption and traps during bulk operations enable breaking internal VM state.
  GHSA-2hw9-mc66-jc2q

46.0.3

Released 2026-08-20

Fixed

• Guest controlled-size host heap allocation through WASIp3 streams.
  GHSA-x84v-gj2h-g759

• Filesystem sandbox escape when paths or symlinks contain trailing slashes.
  GHSA-vqjp-4c8c-hfgg

46.0.2

Released 2026-07-31.

Fixed

• Stores can mix up type indices between engines.
  GHSA-hgjw-h833-99q9

• Preemption and traps during bulk operations enable breaking internal VM state.
  GHSA-2hw9-mc66-jc2q

36.0.17

Released 2026-10-02.

Fixed

• WASI preview 0 implementation of poll_oneoff circumvents fuel consumption.
  GHSA-j366-h8gg-77pm

• Excessive allocated memory on the host when guests don't have stdio.
  GHSA-gqmc-89g8-p25r

• fd_readdir copies uninitialized struct padding into guest memory.
  GHSA-96f6-r43r-8c24

36.0.16

Released 2026-09-24.

Fixed

• Fix fuel spend for dynamic record lifting.
  GHSA-jqpg-j7w6-42pr

• Fix host memory exhaustion on outgoing HTTP body write.
  GHSA-c9gc-w9vx-w86p

• wasmtime-wasi: Fix panic on out-of-range datetimes in WASI filesystem set-times, set-times-at.
  GHSA-j2g9-4prp-pf6h

36.0.15

Released 2026-09-10

Changed

• Wasmtime's internal implementation of wasmtime-wasi no longer depends on
  cap-std crates for the underlying implementation. Instead the cap-std
  implementation was vendored into wasmtime-wasi. This is intended to have no
  visible side effects or result in any behavior changes.
  #14219

36.0.14

Released 2026-08-20

Fixed

• Filesystem sandbox escape when paths or symlinks contain trailing slashes.
  GHSA-vqjp-4c8c-hfgg