Amex's FaaS Uses WebAssembly Instead of Containers

"A key reason behind Amex's adoption of WebAssembly is that WebAssembly demonstrated superior performance metrics compared to containers."

Wasm faster than containers? I guess they mean under there specific circumstances. Rust or C on a Linux container running machine code should definitely be faster than Wasm bytecode.

I wonder what source language they are using that will be compiled to WebAssembly. I also wonder how they built their FaaS infrastructure. A possibility is that they used the open source Firecracker (written in Rust) which powers AWS Lambda.