It's 100kg officially. Down from 160kg (so from around 200L, to about 130L)
It's also limited to a delivery of 100kg/hr. (you might notice that races aren't 1hr long)
I thought this was a rather genius way of limiting engine power and boost. It's also not exactly what anyone would recognise as fuel efficient (about 1.5km/L up from about 1km/L)
It's more likely they'll turn the boost down a bit for the race to save fuel and crank it up for quali.
There has almost always been an element of saving fuel. They never carry more than what's needed, so some races they don't fill the tank. They often throw in a little less and roll the dice on a safety car showing up. If that doesn't happen they can have a bit of a panic.
Being more fuel efficient necessarily means less power. It also means less weight though, which means an advantage in the early stages of the race.
There's a lot involved. The fuel limits is one of my favourites.
My car probably makes 1/3 the power but it's 10x more efficient than an F1 car. They have a long way to go before we have to worry about hippies ruining the sport