They are currently developing the methalox Raptor [1] engine that is planned to have 2300kN sealevel thrust. That would be more than six times powerful than the Merlin 1D+s in current Falcon 9. That would be solidly in the heavy lift rocket engine category, specifically as they intend to group them like they group engines in Falcon 9.<p>[1]: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Raptor_(rocket_engine)" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Raptor_(rocket_engine)</a>