Our current "supported" version range for typescript is

Supporting as old as 3.2.1 puts a burden on us in regards to the typescript APIs that we're able to use.
3.2.1 was published November 29, 2018, and it doesn't support some the APIs we want to use for performance improvements (eg #1759).

We should review with the help of the TS folks to determine a "good enough" minimum version to set for our (eventual) 3.0.0 release.