Simon Willison released pwasm 0.2a0, a pure-Python WebAssembly engine he originally vibe-coded with AI models in January, which Claude Opus 5.5 has since extended over 42 commits to cover most of the WASM spec and bundle working builds of MicroPython, QuickJS, and Micro QuickJS.
# Release: pwasm 0.2a0
Source: [https://simonwillison.net/2026/Oct/1/pwasm/](https://simonwillison.net/2026/Oct/1/pwasm/)
pwasm is one of my folly projects \- an entirely vibe\-coded pure Python WebAssembly engine that I built in January during my first bout of[AI mania](https://simonwillison.net/2026/Sep/27/2026-in-llms-so-far/#simon-willison-2026-in-llms.012.webp)\.
I hadn't touched it since January, so I decided to let Claude Opus 5\.5 loose on it and see if it could make any significant improvements:
> `Evaluate current state of pwasm \- then consider what it would take to get the MicroPython and micro JavaScript experiments from the research repo working under it \- and what it would take to speed it up`
[42 commits later](https://github.com/simonw/pwasm/pull/12)\(with minimal follow\-up prompting\) it now handles almost all of the WASM specification, and the wheel from PyPI bundles working WASM builds of[MicroPython](https://micropython.org/),[QuickJS](https://github.com/quickjs-ng/quickjs)and[Micro QuickJS](https://github.com/bellard/mquickjs)\.
I wouldn't trust this thing at all \- hence the alpha version tag \- but it's interesting seeing how today's models can improve on the work of models from 10 months ago\.
micropython-wasm 0.1a1 is an alpha release that ports MicroPython to WebAssembly, enabling Python execution in web browsers with sandboxing capabilities.
SpaceWASM is an open-source WebAssembly interpreter from NASA/JPL designed for on-board spacecraft sequencing, with a focus on deterministic memory usage and streaming capabilities for resource-constrained environments.