Exhibit 99.1 Investor Relations Contact Monica Prokocki VP of Finance & Investor Relations 602-767-2100 investor.relations@lifestance.com LifeStance Reports Fourth Quarter and Full Year 2023 Results SCOTTSDALE, Ariz. – February 28, 2024 – LifeStance Health Group, Inc. (Nasdaq: LFST), one of the nation’s largest providers of outpatient mental healthcare, today announced financial results for the fourth quarter and full year ended December 31, 2023. (All results compared to prior-year comparative period, unle ...