It was fixed for all valid Unicode characters, you can still get an error when print a surrogate character to the stderr on Linux:

>>> import sys
>>> print('\ud800', file=sys.stderr)
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    print('\ud800', file=sys.stderr)
UnicodeEncodeError: 'utf-8' codec can't encode character '\ud800' in position 0: surrogates not allowed

In the Python REPL you get an escaped sequence.

>>> import sys
>>> print('\ud800', file=sys.stderr)
\ud800