In theory you can, but in practice it would make your code very messy. If your dependency is using runtime A and you are using runtime B - how would they intera

In theory you can, but in practice it would make your code very messy. If your dependency is using runtime A and you are using runtime B - how would they interact? Runtimes like tokio also provide convenience macros for you main mehtod, kind of locking you into them (I think), at least for that codepath. If your application has two parts or binaries that are completely separate you could potentially use two different runtimes, but otherwise I don't think it would make sense. And even then, it would just be a mess. Right now, your runtime is essentially picked for you by your dependencies.