Download Wasmtime 40.0.0

40.0.0
Released 2025-12-20.
Added
- WASIp3 support for wasi:http now implements Response::from_http to convert
from standard Rust types to WASI types.
#12063
- Cranelift now supports a "patchable" ABI which has a maximum number of
arguments and clobbers no registers. This is paired as well with a new
patchable_call instruction which supports being turned into NOPs at runtime.
#12061
#12101
Changed
- Support for the WebAssembly threads proposal is now classified as tier 2 by
default. Additionally creation of SharedMemory is disabled by deafult behind
a new config knob/CLI flag.
#12036
- A variety of peephole-style optimizations have been added to Cranelift's
optimization passes.
#11994
#11995
#11996
#11997
#11998
#11999
#12000
#12006
#12008
- Component host functions have been slightly optimized to remove an Arc clone
and reduce contention.
#11987
- Support for component-model-async has been updated to account for the
changes specified in WebAssembly/component-model#578.
This means that historical binaries using WASIp3, for example, are no longer
valid. Recompilation of historical components will be required and
source-level changes may also be required in some circumstances.
#12031
#12043
- The UnsyncBoxBody type is now used everywhere in wasmtime-wasi-http instead
of just in the wasip3 support.
#12060
- Initial groundwork for gracefully handling OOM (e.g. returning an error
instead of aborting) has been added.
#12070
#12089
- Wasmtime will create a private copy of code memory when guest debugging is
enabled to assist with modifying code when adding/removing breakpoints.
#12051
- The ResourceTable type will no longer use Tombstone when compiled in debug
mode.
#12114
- Intra-component future/stream reads/writes will now trap instead of
accidentally being allowed.
#12117
- Cranelift optimization rules have been tweaked after it was discovered that
they could pessimize code containing long chains of computations.
#12116
Fixed
- Compilation of i8x16.popcnt has been fixed in Winch for some potential
inputs.
#12010
- A panic in Instance::prepare_call for some component-model-async situations
has been fixed.
#12054
- An off-by-one error for lifting/lowering enums/variants with 255 cases has
been fixed.
#12066
- Restarting the read of a host future after cancellation has been fixed.
#12093
- Compilation for OpenBSD on x86_64 has been fixed.
#12097
- Components containing a module type which exoprts a tag are now supported.
#12125