I’m not that deep in the JS ecosystem or runtimes, but I’m a little surprised by some of the claims here about being smaller, having fast starts, sandboxing, performance-competitive, etc.

Does anyone have a sense of what insights, design choices, big bets, etc, unlock all these advantages against already mature and highly optimised JS stacks?

This project appears to be an LLM-rewritten Elk (https://github.com/cesanta/elk), as noted elsewhere in the thread. That project was established in 2019.