Wasmtime 49.0.0 download

## 49.0.0

Released 2026-09-21.

### Added

• Winch now has initial experimental support for the WebAssembly
exception-handling proposal.
[#14066](https://github.com/bytecodealliance/wasmtime/pull/14066)
[#14081](https://github.com/bytecodealliance/wasmtime/pull/14081)
[#14132](https://github.com/bytecodealliance/wasmtime/pull/14132)
[#14149](https://github.com/bytecodealliance/wasmtime/pull/14149)
[#14180](https://github.com/bytecodealliance/wasmtime/pull/14180)
[#14209](https://github.com/bytecodealliance/wasmtime/pull/14209)

• Wasmtime's type reflection APIs for WebAssembly GC types now have dedicated
enums for `Heap{Top,Bottom}Type`s.
[#14208](https://github.com/bytecodealliance/wasmtime/pull/14208)

• Wasmtime now supports the use of environment variables to configure most CLI
arguments in addition to the preexisting CLI flags.
[#14217](https://github.com/bytecodealliance/wasmtime/pull/14217)

• Cranelift will now fold `u{add,mul}_overflow` results combined with `brif`
instructions for more optimal codegen.
[#14217](https://github.com/bytecodealliance/wasmtime/pull/14217)
[#14254](https://github.com/bytecodealliance/wasmtime/pull/14254)

• Components can be tested for equality with a new `Component::same` API.
[#14257](https://github.com/bytecodealliance/wasmtime/pull/14257)

• The Wasmtime C/C++ API now supports the `component-model-implements` feature.
[#14264](https://github.com/bytecodealliance/wasmtime/pull/14264)

• Cranelift will now emit the `{u,s}bfm` instructions on AArch64.
[#14187](https://github.com/bytecodealliance/wasmtime/pull/14187)

### Changed

• The wide-arithmetic WebAssembly proposal is now enabled by default.
[#14110](https://github.com/bytecodealliance/wasmtime/pull/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](https://github.com/bytecodealliance/wasmtime/pull/14215)

• Wasmtime's WASI implementation will no longer over-read stdin where possible.
[#14077](https://github.com/bytecodealliance/wasmtime/pull/14077)

• Wasmtime's WASIp2 implementation now maps host-level "broken pipe" errors to
`StreamError::Closed`.
[#14107](https://github.com/bytecodealliance/wasmtime/pull/14107)

• Wasmtime's WASIp2 implementation of `wasi:http` now validates ports in the
same manner as wasip3.
[#14123](https://github.com/bytecodealliance/wasmtime/pull/14123)

• Wasmtime's WASI implementation of `wasi:filesystem` now returns the
`is-directory` error in some situations when a file is provided.
[#14135](https://github.com/bytecodealliance/wasmtime/pull/14135)

• The `wasmtime-wasi-http` crate now has the `p3` feature enabled by default.
[#14137](https://github.com/bytecodealliance/wasmtime/pull/14137)

• Wasmtime's WASIp2 implementation of `wasi:http` now runs more hooks from the
`WasiHttpHooks` trait in the same manner as wasip3.
[#14167](https://github.com/bytecodealliance/wasmtime/pull/14167)

• Wasmtime now requires Rust 1.96.0 to compile.
[#14184](https://github.com/bytecodealliance/wasmtime/pull/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](https://github.com/bytecodealliance/wasmtime/pull/14146)
[#14250](https://github.com/bytecodealliance/wasmtime/pull/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](https://github.com/bytecodealliance/wasmtime/pull/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](https://github.com/bytecodealliance/wasmtime/pull/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](https://github.com/bytecodealliance/wasmtime/pull/14302)

• The compile-time performance of the alias analysis in Cranelift has been
greatly improved.
[#14306](https://github.com/bytecodealliance/wasmtime/pull/14306)