Tonight say first one while driving home. It was in front of me and a TCH was alongside it. It's definitely smaller on the outside than the TCH.

 

What I remember reading when it was announced is that it is based on the Prius not the TCH. The Lexus version of the TCH will be the ES class and probably not until the next gen TCH comes out.

 

Sounds like the drivetrain is very much adapted from the TCH though, with a few tweaks from the '10 Prius:

"The quick and responsive HS 250h is powered by an all-new Lexus Hybrid Drive system built around a highly efficient 2.4-litre, four-cylinder Atkinson-cycle engine. Combined with the high-torque electric motor, the HS delivers an impressive 187 total system horsepower, along with anticipated fuel efficiency and low emissions ratings akin to that of a subcompact car.
Several other Lexus-first innovations further enhance efficiency and help reduce its environmental impact. A new exhaust heat recovery system accelerates engine warm up time, making for rapid cabin heating in winter and reduces the amount of time the gas engine is used."

 

Yup, uses the TCH drivetrain in a Prius based chassis. It's Toyota's/Lexus' modus operandi, Put the larger or next size up engine into a Toyota platform and then add the parts that make it a Lexus.

I know it sounds liek a cheap shot at Lexus, but it is not meant to be. They have set the Lexus brand to be a 'performance' as well as luxury marque, so we won't see the 2.5 I4 in the Lexus ESh, it will be the 3.x V6. If they do put in the 2.5, they just might see me at the local Lexus dealer upgrading my TCH.