Wasmtime Files

42.0.0

Released 2026-02-20.

Added

• Cranelift now supports bitwise operations on floats on aarch64. #12326

• Cranelift now supports NaN canonicalization of f16 and f128. #12337

• Wasmtime has gained minimal support to implement fixed-length lists in the component model being communicated between composed components. #10619

• Wasmtime's Error and Result types are now built-in to the wasmtime crate and are no longer defined by the anyhow crate. Wasmtime exports a mostly-compatible anyhow-like API at wasmtime::error which is used instead. Wasmtime's own Error handles OOM internally and is foundational part of Wasmtime's work-in-progress support to gracefully handle OOM. #12309

• Wasmtime now exports an extension trait to convert anyhow::Result<T> into wasmtime::Result<T>. #12255

• Wasmtime supports a new bindgen! option to generate bindings specifically with anyhow::Result instead of wasmtime::Result. #12331

• The Nvidia-Cuda execution provider is now supported for the wasi-nn onnx backend. #12044

• Non-exported and private entities can now be accessed through the debugger API. #12367

• A new Store::try_new API has been added which handles OOM. #12415

• Initial configuration knobs for record-and-replay support have been added. #12375

• Cranelift's s390x backend now has support for instructions added in z17. #12319

• Wasmtime's implementation of fibers can now be compiled on riscv32imac platforms. #12506

• Wasmtime's implementation of WASI now correctly limits resource consumption on behalf of the guest, such as host-allocated memory, by default. This means that some behaviors previously allowed by Wasmtime are now disallowed by default if they rely on transferring a large amount of data from the guest to the host. Additionally calls to wasi:random/random.get-random-bytes, for example, now have limits in place by default to avoid allocating too much memory on the host. For more information on this see the related security advisory with further details on knobs added and what behaviors are now restricted by default. GHSA-852m-cvvp-9p4w

Changed

• Reentrance rules for WebAssembly components have changed in accordance with upstream specification changes. Embeddings are not expected to be affected, but please reach out if you find problems. #12349

• Wasmtime's Config::async_support option is now removed and no longer necessary. Embeddings can likely just remove turning this on and everything should keep working like normal. #12371

• Wasmtime now supports Config::concurrency_support as a knob to enable or disable *_concurrent APIs at runtime when the component-model-async crate feature is enabled. #12416

• The post_return-style functions in Wasmtime's API are now noops and will be removed in the future. #12498

• Translation of global.get of a defined, immutable global is now turned into a CLIF constant. #12234

• The wasmtime-wasi-nn crate's dependency on ort has been updated. #12162

• Error bounds requiring using hyper::Error in wasmtime-wasi-http have been relaxed to taking E: Into<ErrorCode> instead. #12227

• The cranelift-assembler-x64, and cranelift-isle crates now supports no_std targets. The cranelift-codegen crate now mostly supports no_std, but not entirely. #12222 #12235 #12236

• Android release binaries are now compiled with a larger page size configured. #12246

• Implicit binds are now allowed for WASIp3 sockets. #12225

• Wasmtime's implementation of component-model-async now correctly checks for whether tasks are allowed to block in all guest-to-guest situations. #12282

• The wasmtime-wasi-tls crate now has an OpenSSL backend. #12228

• Wasmtime's OutOfMemory error now keeps track of the attempted allocation size that failed. #12351

• Wasmtime's *_unchecked functions now work with MaybeUninit<ValRaw> instead of ValRaw directly. #12366

• Wasmtime now requires Rust 1.91.0 to compile. #12392

• Wasmtime's management of component-model-async tasks is now consistently done in all boundaries between guest/host tasks. #12379

Fixed

• The HeapType::matches implementation for NoExn has been fixed. #12350

• Enum discriminant validation for composed components has been fixed. #12356

• Shifts in some situations on aarch64 with Winch have been fixed. #12501

• Debug value locations around cold blocks have been improved. #12484

• Panics when adding too many headers to a wasi:http/types.fields has been resolved GHSA-243v-98vx-264h