Prior to the Mortal Kombat 1 beta access beginning, developer NetherRealm Studios will be running an Online Stress Test. This will be available on consoles like PS5 and will begin on 23rd June, 2023 and will run through 26th June, 2023. This is separate from beta access, and to participate you'll need to register on Warner Bros' official website. This does not, however, guarantee access.
The Online Stress Test will include four playable characters and Kameos, and its file size will weigh in at around 6.8GB on PS5. It'll feature single player Klassic Towers mode, as well as online one-on-one versus features, although there won't be crossplay in this specific build.