This aims to be a tracking issue for all work necessary to support the free-threaded build of Python 3.13. A very high-level list of steps is (more details to follow as I investigate more issues):

• Set up CI for free-threading
  • CI: Set up CI for the free-threaded build of 3.13 #59058
• Audit C extension module for thread-safety issues
  • pandas_datetime is thread-safe
  • pandas_parser is not thread-safe, but cannot be used in multiple threads from within pandas Python code.
• Test Cython extension modules (with Freethreading thread safety cython/cython#6226)
  • Everything appears to be okay (green CI) both with Cython nightly and with the above Cython PR!
• Mark C extension modules as thread-safe with the Py_mod_gil slot
  • Add Py_mod_gil slot to C extension modules #59135
  • ENH: Globally enable Cython free-threading directive #59248
• Upload nightly wheels for the free-threaded build
  • Upload 3.13 & free-threaded nightly wheels #59136