diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index e947689c3..347993e79 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -53,6 +53,8 @@ jobs:
             tox_env: py312-full
           - python: '3.13'
             tox_env: py313-full
+          - python: '3.13t'
+            tox_env: py313
           - python: '3.14.0-alpha.1 - 3.14'
             tox_env: py314-full
           - python: 'pypy-3.10'
@@ -67,10 +69,17 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         name: Install Python
+        if: matrix.python != '3.13t'
         with:
           python-version: ${{ matrix.python}}
+      - name: Install Python
+        uses: deadsnakes/action@e640ac8743173a67cca4d7d77cd837e514bf98e8  # v3.2.0
+        if: matrix.python == '3.13t'
+        with:
+          python-version: '3.13'
+          nogil: true
       - name: Install apt packages
-        run: sudo apt-get update && sudo apt-get install libcurl4-openssl-dev
+        run: sudo apt-get update && sudo apt-get install libcurl4-openssl-dev pkg-config libffi-dev
       - name: Install tox
         run: python -m pip install tox -c requirements.txt
 
diff --git a/setup.py b/setup.py
index 0b175af85..a860d5747 100644
--- a/setup.py
+++ b/setup.py
@@ -18,7 +18,7 @@
 import os
 import platform
 import setuptools
-
+import sysconfig
 
 kwargs = {}
 
@@ -35,6 +35,16 @@
     platform.python_implementation() == "CPython"
     and os.environ.get("TORNADO_EXTENSION") != "0"
 ):
+    # build with Py_LIMITED_API unless in freethreading build (which does not currently
+    # support the limited API in py313t)
+    if not sysconfig.get_config_var("Py_GIL_DISABLED"):
+        extension_kwargs = dict(
+            py_limited_api=True, define_macros=[("Py_LIMITED_API", "0x03090000")]
+        )
+        kwargs["options"] = {"bdist_wheel": {"py_limited_api": "cp39"}}
+    else:
+        extension_kwargs = {}
+
     # This extension builds and works on pypy as well, although pypy's jit
     # produces equivalent performance.
     kwargs["ext_modules"] = [
@@ -45,14 +55,11 @@
             # fall back to the pure-python implementation on any build failure.
             optional=os.environ.get("TORNADO_EXTENSION") != "1",
             # Use the stable ABI so our wheels are compatible across python
-            # versions.
-            py_limited_api=True,
-            define_macros=[("Py_LIMITED_API", "0x03090000")],
+            # versions if not in freethreading build
+            **extension_kwargs,
         )
     ]
 
-    kwargs["options"] = {"bdist_wheel": {"py_limited_api": "cp39"}}
-
 
 setuptools.setup(
     name="tornado",
diff --git a/tornado/test/circlerefs_test.py b/tornado/test/circlerefs_test.py
index d5f7e9692..5ae7ccaab 100644
--- a/tornado/test/circlerefs_test.py
+++ b/tornado/test/circlerefs_test.py
@@ -19,7 +19,7 @@
 
 import tornado
 from tornado import web, gen, httpclient
-from tornado.test.util import skipNotCPython
+from tornado.test.util import skipNotCPython, skipFreeThreaded
 
 
 def find_circular_references(garbage):
@@ -102,6 +102,7 @@ def assert_no_cycle_garbage():
 
 # GC behavior is cpython-specific
 @skipNotCPython
+@skipFreeThreaded
 class CircleRefsTest(unittest.TestCase):
     def test_known_leak(self):
         # Construct a known leak scenario to make sure the test harness works.
diff --git a/tornado/test/util.py b/tornado/test/util.py
index 25dd2000f..e205b6b69 100644
--- a/tornado/test/util.py
+++ b/tornado/test/util.py
@@ -3,6 +3,7 @@
 import platform
 import socket
 import sys
+import sysconfig
 import textwrap
 import typing
 import unittest
@@ -23,6 +24,9 @@
 skipNotCPython = unittest.skipIf(
     platform.python_implementation() != "CPython", "Not CPython implementation"
 )
+skipFreeThreaded = unittest.skipIf(
+    sysconfig.get_config_var("Py_GIL_DISABLED"), "Freethreaded Python build"
+)
 
 
 def _detect_ipv6():
diff --git a/tox.ini b/tox.ini
index d80f7275a..75feafc06 100644
--- a/tox.ini
+++ b/tox.ini
@@ -58,6 +58,8 @@ setenv =
        # (New in python 3.10, becomes obsolete when utf8 becomes the
        # default in 3.15)
        PYTHONWARNDEFAULTENCODING=1
+       # force the GIL on
+       PYTHON_GIL=1
 
 # Allow shell commands in tests
 allowlist_externals = sh, env