Acknowledging the test failure and message pointing to #32394:

======================================================================
FAIL: test_new_tcp_flags (test.test_socket.TestMSWindowsTCPFlags)
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Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_socket.py", line 5992, in test_new_tcp_flags
    self.assertEqual([], unknown,
AssertionError: Lists differ: [] != ['TCP_KEEPALIVE']
Second list contains 1 additional elements.
First extra element 0:
'TCP_KEEPALIVE'
- []
+ ['TCP_KEEPALIVE'] : New TCP flags were discovered. See bpo-32394 for more information
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It appears that TCP_KEEPALIVE is defined in Windows (in ws2ipdef.h) despite not being documented on https://docs.microsoft.com/en-us/windows/desktop/winsock/ipproto-tcp-socket-options 

Given that TCP_KEEPIDLE is #define as the value of TCP_KEEPALIVE, I'd guess that it was added at the same time in which case it probably ought to be added to win_runtime_flags for exclusion based on the same Windows version 1709 too. 

steve.dower: I've added you to the nosy list based on your active participation in #32394. Any thoughts on this one?