According to the project page [1], WebGL. WebGPU is still in development, it's the successor of WebGL and not yet supported by stable browsers.

[1] http://www.continuation-labs.com/projects/d3wasm/

This port uses WebGL. There are no games out there yet that are using WebGPU in production, it's only available in Origin Trial. It goes live by default in Chrome February 2023.