Mazda (of which Toyota has a fair stake) is rolling out their second generation SkyActiv which uses spark controlled compression ignition (SPCCI), in conjunction with a lean supercharger, to switch between spark ignition and compression ignition based on engine load. They've not thrown out a thermal efficiency number, but it's likely in the ballpark of 43-45%. They're targeting 56% thermal efficiency for the third generation of the tech, which is already well into its development, and we'll see sometime after 2021.
The current benchmark is Mercedes' Formula 1 engines, which are 50% thermally efficient, but understandably cost an arm and a leg.
This is excluding other things like Koenigsegg's FreeValve which uses pneumatic-hydraulic-electronic actuators (PHEA) to replace the camshaft. The only licensee so far is the Chinese manufacturer Qoros, which is a shame as Koenigsegg got pretty significant adoption of their FlexFuel tech by GM, Ford and Chrysler in the US (> 17 million vehicles sold).
(I am comparing just the weights of the power plants, not the power plant + drivetrain which would include gearboxes, differentials and electric motors).