>>> import typing
>>> T = typing.TypeVar('T')
>>> P = typing.ParamSpec('P')
>>> C = typing.Callable[P, T]
>>> C[int, str, float]
typing.Callable[[int], str]

int substitutes P as [int], str substitutes T, and the third argument float is ignored.

If Callable is nested, it works as expected:

>>> typing.List[C][int, str, float]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython/Lib/typing.py", line 309, in inner
    return func(*args, **kwds)
           ^^^^^^^^^^^^^^^^^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 1028, in __getitem__
    _check_generic(self, params, len(self.__parameters__))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 231, in _check_generic
    raise TypeError(f"Too {'many' if alen > elen else 'few'} parameters for {cls};"
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: Too many parameters for typing.List[typing.Callable[~P, ~T]]; actual 3, expected 2

collections.abc.Callable raises an error too.

There is also similar bug in Generic:

>>> from typing import *
>>> T = TypeVar("T")
>>> P = ParamSpec("P")
>>> class X(Generic[T, P]):
...     f: Callable[P, int]
...     x: T
... 
>>> P_2 = ParamSpec("P_2")
>>> X[int, P_2, str]
__main__.X[int, ~P_2]

New changeset f92b9133ef67e77605cbd315b6b6c81036ce110e by Serhiy Storchaka in branch 'main':
bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter. (GH-27515)
https://github.com/python/cpython/commit/f92b9133ef67e77605cbd315b6b6c81036ce110e

New changeset c8db292012dd84aab81eb3ed9146709696a3d290 by Miss Islington (bot) in branch '3.10':
bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter. (GH-27515)
https://github.com/python/cpython/commit/c8db292012dd84aab81eb3ed9146709696a3d290