Parallel and Asynchronous Code compatibility on shinyapps.io plans

Hi RStudio Community,
I'm wondering if someone could clarify as to what the capabilities of the shinyapp.io resource tiers are in regards to running in parallel with future/furrr or using asynchronous code with future/promises.
By the sound of the Performance Boost feature on tiers >= Basic:

Multiple worker processes per application, up to 8GB of RAM and the ability to add additional instances to keep your applications responsive as more people use them.

it seems like parallelization and asynchronous code will only work on these tiers and not on the tiers < Basic since those are single threaded.

Is this true? Is anyone using parallelized or asynchronous code that can confirm or elaborate on what the situation is with package functionality that relies on multi-threaded operations?