Type hints with user defined classes

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The former is correct, if arg accepts an instance of CustomClass:

def FuncA(arg: CustomClass):
    #     ^ instance of CustomClass

In case you want the class CustomClass itself (or a subtype), then you should write:

from typing import Type  # you have to import Type

def FuncA(arg: Type[CustomClass]):
    #     ^ CustomClass (class object) itself

Like it is written in the documentation about Typing:

class typing.Type(Generic[CT_co])

A variable annotated with C may accept a value of type C. In
contrast, a variable annotated with Type[C] may accept values that
are classes themselves – specifically, it will accept the class
object of C.

The documentation includes an example with the int class:

a = 3         # Has type 'int'
b = int       # Has type 'Type[int]'
c = type(a)   # Also has type 'Type[int]'

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