Zaheer from Levels.fyi here. Argo AI & Duolingo are based out of Pittsburgh. Uber & Google also have a decent sized presence. Some more context on their tech scene here: https://www.reuters.com/article/us-pittsburgh-tech/a-tech-bo...
From what I can remember, Microsoft (Azure Storage), Amazon (ML Alexa Teams), Google, Uber (ATG), Argo AI, Aurora, Facebook (Oculus), Duolingo, and Apple are all have offices in the city.
In the suburbs I think Netapp and Oracle have offices.