Since the vast majority of my classical music listening is from, say, post WWII to the contemporary era, I am constantly discovering new composers.
Erkki-Sven Tüür from Estonia is a recent discovery for me. I am loving his Violin concerto, "Zeitraum for orchestra", "Aditus (for orchestra)" among others.
Ann Thorvaldsdottir is another very recent discovery. "Aeriality", "Hrim", "Ro", and others. Very haunting and atmospheric.
Andrew Norman is yet another. I really like his percussion concerto, "Switch". Also, "Mine, Mime, Meme" for flute, clarinet, violin, cello, piano, percussion, "Light Screens", "Spiral". Pretty much everything I've heard of Norman's.
Augusta Read Thomas is another. I only have one piece from her, "EOS (Goddess of Dawn)", but it is excellent.
The nice thing about the Augusta Read Thomas piece, is it is on a Reference Recording with Andrew Norman's "Switch" and a great piece by Nico Muhly, "Control (Five Landscapes for Orchestra) ". Great music, on an audiophile recording.
As far as a new performer discovery, that would be, Eighth Blackbird. A contemporary music ensemble from Chicago.
Their latest, "Hind, Eye" is amazing! I also have "Strange Imaginary Animals", which is almost as good.
They record on Cedille Records, a label I am not familiar with, but the recording is extremely good. Incredible imaging and soundstage.