Seems most sites speculate its the 'hardcore road car'...

"This prototype boasts canards on its front bumper and an upsized rear wing, suggesting that it might be the GRMN variant, rather than the "basic" GR Yaris.
GRMN stands for "Gazoo Racing Meisters of the Nürburgring," after all, so it makes all the sense in the world that Toyota's motorsports development specialists would take their prototype to its namesake road course."