I'm still confused. Why not just pour a ton of resources into it since it's open source. I guess dev mindshare? It is a great product

You're describing Node.js which has existed for the last 15 years

but they are a company that burns billions every year in losses and this seems like a pretty random acquisition.

Bun is the product that depends on providing that good, stable, cross-platform JS runtime and they were already doing a good job. Why would Anthropic's acquisition of them make them better at what they were already doing?

Ok but node is even more stable and mature - compare node api parity in bun and also issue of bun vs node

That doesn’t require or benefit from acquiring Bun. Node continues to exist and serve fine.