The L402 payment protocol has been in production use for several years at Lightning Labs.

At Fewsats, we've explored various applications of L402 like wrapping storage/compute as a service. We've found that one of the most promising areas for L402 is in providing Data APIs though.

I think the protocol shows particular promise for AI applications, especially in agent environments but it's worth noting that we're still in the early stages of exploring these use cases.

Long story short, I would say that while L402 is production-ready, there hasn't yet been a "killer app" built on it.