diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 7d5d7c10..5ab27ced 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -24,7 +24,7 @@ jobs:
       matrix:
         os: [Ubuntu, Windows, macOS]
         python_version:
-          ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14", "pypy3.8", "pypy3.9", "pypy3.10", "pypy3.11"]
+          ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14", "3.13t", "3.14t", "pypy3.8", "pypy3.9", "pypy3.10", "pypy3.11"]
         include:
           - os: Ubuntu
             python_version: "3.11.0"
diff --git a/noxfile.py b/noxfile.py
index 046ec14f..a8adfb51 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -34,6 +34,8 @@
 @nox.session(
     python=[
         *PYTHON_VERSIONS,
+        "3.13t",
+        "3.14t",
         "pypy3.8",
         "pypy3.9",
         "pypy3.10",
diff --git a/pyproject.toml b/pyproject.toml
index de92ac7b..eeb5f841 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,6 +26,7 @@ classifiers = [
   "Programming Language :: Python :: 3.14",
   "Programming Language :: Python :: Implementation :: CPython",
   "Programming Language :: Python :: Implementation :: PyPy",
+  "Programming Language :: Python :: Free Threading :: 4 - Resilient",
   "Typing :: Typed",
 ]
 dependencies = []
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 00000000..1d6cbdf3
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,10 @@
+from __future__ import annotations
+
+import sysconfig
+
+
+def pytest_report_header() -> str:
+    lines = [f"sysconfig platform: {sysconfig.get_platform()}"]
+    if sysconfig.get_config_var("Py_GIL_DISABLED"):
+        lines.append("free-threaded Python build")
+    return "\n".join(lines)