The beta is now out. The big incompatible change is probably PyCode_New() (in order to support positional only parameters). At least Cython is broken by this change, probably other extensions. Hopefully it will not be long for that to be fixed.
Lots of other neat changes. The f-string debugging with '=' will be handy. There are a number of minor speedups and so this should be the fastest Python yet released.
* `python -m asyncio` gives a async repl that supports top level await statements.
* unittest.mock now has AsyncMock that can mock async for, async with and other async related code.
* math.comb to compute binomial coefficients. math.perm and math.isqrt were added.
* unittest gained support for async test case.
* importlib.metadata got merged providing API to access package metadata.
* Threading module now has an API to get native thread ID.
* multiprocessing.parent_process got added.
PEPs merged. 4 PEPs were merged in a single day with a week before beta release.
* [Runtime audit hooks got merged PEP 578](https://bugs.python.org/issue36842)
* typing related PEPs were merged : Add final qualifier (PEP 591), Literal types (PEP 586) and TypedDict (PEP 589)
* [Python embedding got better with PEP 587](https://bugs.python.org/issue36763)
* [Vectorcall for functions got merged PEP 590](https://bugs.python.org/issue36922)
* [New pickle protocol with performance improvements PEP 574](https://bugs.python.org/issue36785)