# Swift for Wasm September 2026 Updates **URL:** \ **Category:** Swift for WebAssembly\ **Created:** [September 30, 2026, 3:22pm UTC](https://forums.swift.org/t/swift-for-wasm-september-2026-updates/89836 "2026-09-30T15:22:38Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Max\_Desiatov](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/max_desiatov/32/20654_2.png) [@Max\_Desiatov](https://forums.swift.org/u/Max_Desiatov)\ **Post date:** [September 30, 2026, 3:22pm UTC](https://forums.swift.org/t/swift-for-wasm-september-2026-updates/89836/1 "2026-09-30T15:22:38Z")
Notable changes this month: WasmKit 0.4.0 made its interpreter about twice as fast and runs on microcontrollers, and 0.4.1 added the typed function references proposal; JavaScriptKit 0.59.0 can generate packages running on uWASI; uWASI shipped 1.5.0 and 1.6.0; ElementaryUI 0.8.0 added custom element support and `PhaseAnimator`. Many thanks to @AnthonyLatsis, @felipepiovezan, @JDevlieghere, @kateinoigakukun, @krodak, Logan Shire, @scottm, shopifyski, @sliemeobn, Vithanco for contributions! ## Blog Posts - [What's new in Swift: August 2026 Edition](https://www.swift.org/blog/whats-new-in-swift-august-2026/): @sliemeobn introduces the elementary-swift project and ElementaryUI as a guest contributor. The digest also features [SwiftTUI](https://swifttui.sh), which ships one interface as a terminal app, a native app, or a WASI build for the browser. - [WasmKit 0.4.0 - 2x Faster, and Running on Microcontrollers](https://katei.dev/blog/2026/09/18/wasmkit-0-4-0/): @kateinoigakukun walks through the interpreter optimizations behind the release. ## [Swift Toolchain](https://github.com/swiftlang/swift) Toolchain development snapshots built off the `main` branch now includes experimental support for `wasm32-unknown-wasip1-threads` triple in the Wasm Swift SDK. Note that multi-threaded executors are not included in these Swift SDKs yet. See [JavaScriptKit documentation](https://swiftpackageindex.com/swiftwasm/javascriptkit/0.59.0/documentation/javascripteventloop/webworkertaskexecutor) for details on how to set up multi-threaded executors in the browser. - Pass `--no-stack-first` to `wasm-ld` [swift-driver#2179](https://github.com/swiftlang/swift-driver/pull/2179), reapplied in [swift-driver#2185](https://github.com/swiftlang/swift-driver/pull/2185) after the matching LLVM change landed; - `wasiswiftsdk.py`: include `wasip1-threads` in Wasm Swift SDK [swift#87283](https://github.com/swiftlang/swift/pull/87283); - WASI: build Concurrency C++ sources with `-fno-exceptions` in non-Embedded builds too [swift#92171](https://github.com/swiftlang/swift/pull/92171). ## [JavaScriptKit](https://github.com/swiftwasm/JavaScriptKit) [0.59.0](https://github.com/swiftwasm/JavaScriptKit/releases/tag/0.59.0) lets PackageToJS generate packages that run on [uWASI](https://github.com/swiftwasm/uwasi) through `--wasi-runtime uwasi`, with `@bjorn3/browser_wasi_shim` staying the default for now. BridgeJS also diagnoses a type conforming to a `@JS` protocol that cannot cross to JavaScript, which used to compile and then trap at runtime. On `main`, `@JS("name")` renaming now applies to exported classes, structs, enums, and protocols, `@JS` protocols can refine other protocols, and generic imports accept protocol constraints. - PackageToJS: add selectable uWASI runtime [#811](https://github.com/swiftwasm/JavaScriptKit/pull/811); - BridgeJS: diagnose unsupported protocol conformers before lowering [#812](https://github.com/swiftwasm/JavaScriptKit/pull/812); - BridgeJS: unify thunk argument preparation, fixing incorrect results from struct methods and closures [#813](https://github.com/swiftwasm/JavaScriptKit/pull/813); - BridgeJS: support custom exported type names [#814](https://github.com/swiftwasm/JavaScriptKit/pull/814); - BridgeJS: support protocol refinement and constrained imports [#815](https://github.com/swiftwasm/JavaScriptKit/pull/815). ## [WasmKit](https://github.com/swiftwasm/WasmKit) [0.4.0](https://github.com/swiftwasm/WasmKit/releases/tag/0.4.0) ([announcement](https://forums.swift.org/t/wasmkit-0-4-0-2x-faster-and-running-on-microcontrollers/89665)) roughly doubles interpreter speed: on the [wasmi benchmark suite](https://github.com/wasmi-labs/wasmi-benchmarks) execution time is about half of 0.3.1's. The release also includes the Embedded Swift work of the past two months, with the engine running on an ESP32-C6 and on a Playdate handheld console, adds WASI Threads through `wasmkit run --wasi-threads`, and improves LLDB debugging support. [0.4.1](https://github.com/swiftwasm/WasmKit/releases/tag/0.4.1) followed with the typed function references proposal behind `--feature function-references`, fuel metering to bound guest execution, hardening against untrusted modules found by fuzzing, and a stack frame layout that again runs functions with thousands of locals, which 0.4.0 rejected as too large. - 20+ performance optimization PRs. See the full list at [0.4.0 release page](https://github.com/swiftwasm/WasmKit/releases/tag/0.4.0); - Add WASI Threads `thread-spawn` support [#423](https://github.com/swiftwasm/WasmKit/pull/423); - Fix Embedded Swift builds on ARM and on host platforms [#473](https://github.com/swiftwasm/WasmKit/pull/473); - Implement the typed function references proposal [#480](https://github.com/swiftwasm/WasmKit/pull/480), [#481](https://github.com/swiftwasm/WasmKit/pull/481); - Add fuel metering to bound guest execution [#474](https://github.com/swiftwasm/WasmKit/pull/474); - Support LLDB's updated `qWasmGlobal` packet [#420](https://github.com/swiftwasm/WasmKit/pull/420); - Advertise the `qWasmInstance+` feature LLDB looks for [#422](https://github.com/swiftwasm/WasmKit/pull/422); - Report the guest's exit status, and a trap as a stop, instead of dropping the connection [#424](https://github.com/swiftwasm/WasmKit/pull/424), [#468](https://github.com/swiftwasm/WasmKit/pull/468); - Report a stop at the start of the instruction run [#425](https://github.com/swiftwasm/WasmKit/pull/425); - Bind breakpoint resolution to the containing function [#426](https://github.com/swiftwasm/WasmKit/pull/426); - Support writing guest linear memory [#427](https://github.com/swiftwasm/WasmKit/pull/427); - Answer `qMemoryRegionInfo` with the region containing an address [#428](https://github.com/swiftwasm/WasmKit/pull/428); - Keep a debuggable module off the accumulator hand-off [#479](https://github.com/swiftwasm/WasmKit/pull/479); - Stop untrusted modules and text from aborting or reading past the host [#475](https://github.com/swiftwasm/WasmKit/pull/475); - WASI: resolve guest paths within their descriptor, and answer bad arguments with an errno [#476](https://github.com/swiftwasm/WasmKit/pull/476); - Batch fixes found by fuzzers, and repair the fuzzing harness [#472](https://github.com/swiftwasm/WasmKit/pull/472), [#477](https://github.com/swiftwasm/WasmKit/pull/477); - Put the locals below `sp` so frames with many locals fit [#483](https://github.com/swiftwasm/WasmKit/pull/483); - Make warnings-as-errors opt-in via `WASMKIT_WARNINGS_AS_ERRORS` [#469](https://github.com/swiftwasm/WasmKit/pull/469). ## [ElementaryUI](https://github.com/elementary-swift/elementary-ui) [0.8.0](https://github.com/elementary-swift/elementary-ui/releases/tag/0.8.0) ships the new `ElementaryWebComponents` module, which registers ElementaryUI views as [custom elements](https://elementary.codes/guide/topics/web-components.html). The release also adds a SwiftUI-style `PhaseAnimator` that animates content through a sequence of phases, and DOM event and style modifiers on SVG content. It requires Swift 6.4. - Allow DOM event and style modifiers on SVG content [#119](https://github.com/elementary-swift/elementary-ui/pull/119); - Bump minimum to Swift 6.4 [#129](https://github.com/elementary-swift/elementary-ui/pull/129); - Add `ElementaryWebComponents` for custom element support [#128](https://github.com/elementary-swift/elementary-ui/pull/128); - Add runtime deprecation warning in bundled runtime [#130](https://github.com/elementary-swift/elementary-ui/pull/130); - Minor performance improvements [#131](https://github.com/elementary-swift/elementary-ui/pull/131); - Upgrade to JavaScriptKit 0.59 [#132](https://github.com/elementary-swift/elementary-ui/pull/132); - Add `PhaseAnimator` [#133](https://github.com/elementary-swift/elementary-ui/pull/133). ## [uWASI](https://github.com/swiftwasm/uwasi) Four releases: [1.5.0](https://github.com/swiftwasm/uwasi/releases/tag/1.5.0) ships last month's expanded WASI Preview 1 support and makes every feature a factory, so `useX()` is the only call style, a source-breaking change. [1.5.1](https://github.com/swiftwasm/uwasi/releases/tag/1.5.1) fixes package entry points for resolvers that do not read `exports`, and [1.5.2](https://github.com/swiftwasm/uwasi/releases/tag/1.5.2) adds the `setInstance` and `lineBuffered` APIs that PackageToJS needs for its uWASI option. [1.6.0](https://github.com/swiftwasm/uwasi/releases/tag/1.6.0) lets a host serve file descriptors through `extraFds`. - Fix O(n^2) `fd_write` in `useMemoryFS` [#17](https://github.com/swiftwasm/uwasi/pull/17); - Require the call style for every feature [#19](https://github.com/swiftwasm/uwasi/pull/19); - Report oversize file requests instead of trapping the guest [#20](https://github.com/swiftwasm/uwasi/pull/20); - Declare entry points for resolvers that do not read `exports` [#23](https://github.com/swiftwasm/uwasi/pull/23); - Write all 64 bits of the `clock_res_get` resolution [#25](https://github.com/swiftwasm/uwasi/pull/25); - Add `setInstance` and a `lineBuffered` stdio helper for embedders [#26](https://github.com/swiftwasm/uwasi/pull/26); - Add `extraFds` to `StdioOptions` for character devices beyond stdio [#29](https://github.com/swiftwasm/uwasi/pull/29). ## Other Notable Changes - Support `wasm32-unknown-wasip1-threads` with the pthread executors [swiftlang/swift-platform-executors#33](https://github.com/swiftlang/swift-platform-executors/pull/33). * * * Thank you for reading, and please feel free to add any comments or suggestions if we missed anything! If you'd like to catch up with changes from previous months, here's a list of recent updates: - [August 2026](https://forums.swift.org/t/swift-for-wasm-august-2026-updates/89316); - [July 2026](https://forums.swift.org/t/swift-for-wasm-july-2026-updates/88673); - [June 2026](https://forums.swift.org/t/swift-for-wasm-june-2026-updates/87820); - [May 2026](https://forums.swift.org/t/swift-for-wasm-may-2026-updates/86981); - [April 2026](https://forums.swift.org/t/swift-for-wasm-april-2026-updates/86371).