The WASI SDK is a modified version of the Clang compiler, which uses a library called wasi-libc. This gives programs written in C (and C API-compatible languages) access to WASI’s APIs for the host (storage, networking, timers, etc).
In theory, we should just be able to compile a given CPython release with the most recent WASI SDK at the time. But things aren’t that simple. For one, the SDK’s biggest component, wasi-libc, doesn’t guarantee it’ll be forward- or backward-compatible. Also, some versions of the SDK may cause buggy behavior with some versions of CPython. As developers, we want to know that this version of CPython works with this version of the SDK—or at least be able to document which bugs appear with any given combination of the two.
How future releases of CPython will use WASI
CPython has been available on Wasm since version 3.11, with Tier 2 and Tier 3 support. The more official wasip1 is the better-supported target, while the older emscripten standard is the less-supported version. But Tier 2 support has been confined to the WASI “Preview 1” set of system calls. And for the reasons already stated, the WASI SDK CPython uses is not necessarily the most recent version, either: it’s SDK version 21 for Python 3.11 and 3.12, and SDK version 24 for 3.13 and 3.14.
