The Glimmer runtime is under 30k, and we have not done much bundle optimization yet so hopefully this should go down a little bit even further.
React Fiber is currently just over 70k, and that's just the reconciler, not the complete React package. However, according to Dan Abramov[0] they have not yet focused on optimizing the bundle size either. And Fiber includes some prioritization features that we don't have in Glimmer yet.