diff --git a/Lib/test/test_free_threading/test_itertools.py b/Lib/test/test_free_threading/test_itertools.py
index 2d2d4ff1ca1f6f1..0703c7e5e2916e8 100644
--- a/Lib/test/test_free_threading/test_itertools.py
+++ b/Lib/test/test_free_threading/test_itertools.py
@@ -1,6 +1,13 @@
 import unittest
+from threading import Thread, Barrier
 from itertools import (
+    accumulate,
+    chain,
+    combinations_with_replacement,
+    cycle,
+    permutations,
     tee,
+    zip_longest,
 )
 from test.support import threading_helper
 
@@ -8,6 +15,98 @@
 threading_helper.requires_working_threading(module=True)
 
 
+def work_iterator(it):
+    while True:
+        try:
+            next(it)
+        except StopIteration:
+            break
+
+
+class ItertoolsThreading(unittest.TestCase):
+
+    @threading_helper.reap_threads
+    def test_cycle(self):
+        number_of_threads = 6
+        number_of_iterations = 10
+        number_of_cycles = 400
+
+        barrier = Barrier(number_of_threads)
+        def work(it):
+            barrier.wait()
+            for _ in range(number_of_cycles):
+                _ = next(it)
+
+        data = (1, 2, 3, 4)
+        for it in range(number_of_iterations):
+            cycle_iterator = cycle(data)
+            worker_threads = []
+            for ii in range(number_of_threads):
+                worker_threads.append(
+                    Thread(target=work, args=[cycle_iterator]))
+
+            with threading_helper.start_threads(worker_threads):
+                pass
+
+            barrier.reset()
+
+    @threading_helper.reap_threads
+    def test_chain(self):
+        number_of_threads = 6
+        number_of_iterations = 20
+
+        barrier = Barrier(number_of_threads)
+        def work(it):
+            barrier.wait()
+            while True:
+                try:
+                    next(it)
+                except StopIteration:
+                    break
+
+        data = [(1, )] * 200
+        for it in range(number_of_iterations):
+            chain_iterator = chain(*data)
+            worker_threads = []
+            for ii in range(number_of_threads):
+                worker_threads.append(
+                    Thread(target=work, args=[chain_iterator]))
+
+            with threading_helper.start_threads(worker_threads):
+                pass
+
+            barrier.reset()
+
+    @threading_helper.reap_threads
+    def test_combinations_with_replacement(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = combinations_with_replacement(tuple(range(2)), 2)
+            threading_helper.run_concurrently(work_iterator, nthreads=6, args=[it])
+
+    @threading_helper.reap_threads
+    def test_permutations(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = permutations(tuple(range(2)), 2)
+            threading_helper.run_concurrently(work_iterator, nthreads=6, args=[it])
+
+    @threading_helper.reap_threads
+    def test_accumulate(self):
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = accumulate(tuple(range(40)))
+            threading_helper.run_concurrently(work_iterator, nthreads=10, args=[it])
+
+    @threading_helper.reap_threads
+    def test_zip_longest(self):
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = zip_longest(list(range(4)), list(range(8)), fillvalue=0)
+            threading_helper.run_concurrently(work_iterator, nthreads=10, args=[it])
+
+
+
 class TestTeeConcurrent(unittest.TestCase):
     # itertools.tee branches share a linked list of internal data cells.
     # Concurrent iteration must not corrupt that shared state or crash the
diff --git a/Lib/test/test_free_threading/test_itertools_combinatoric.py b/Lib/test/test_free_threading/test_itertools_combinatoric.py
new file mode 100644
index 000000000000000..5b3b88deedd1210
--- /dev/null
+++ b/Lib/test/test_free_threading/test_itertools_combinatoric.py
@@ -0,0 +1,51 @@
+import unittest
+from threading import Thread, Barrier
+from itertools import combinations, product
+from test.support import threading_helper
+
+
+threading_helper.requires_working_threading(module=True)
+
+def test_concurrent_iteration(iterator, number_of_threads):
+    barrier = Barrier(number_of_threads)
+    def iterator_worker(it):
+        barrier.wait()
+        while True:
+            try:
+                _ = next(it)
+            except StopIteration:
+                return
+
+    worker_threads = []
+    for ii in range(number_of_threads):
+        worker_threads.append(
+            Thread(target=iterator_worker, args=[iterator]))
+
+    with threading_helper.start_threads(worker_threads):
+        pass
+
+    barrier.reset()
+
+class ItertoolsThreading(unittest.TestCase):
+
+    @threading_helper.reap_threads
+    def test_combinations(self):
+        number_of_threads = 10
+        number_of_iterations = 24
+
+        for it in range(number_of_iterations):
+            iterator = combinations((1, 2, 3, 4, 5), 2)
+            test_concurrent_iteration(iterator, number_of_threads)
+
+    @threading_helper.reap_threads
+    def test_product(self):
+        number_of_threads = 10
+        number_of_iterations = 24
+
+        for it in range(number_of_iterations):
+            iterator = product((1, 2, 3, 4, 5), (10, 20, 30))
+            test_concurrent_iteration(iterator, number_of_threads)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2025-03-13-20-48-58.gh-issue-123471.cM4w4f.rst b/Misc/NEWS.d/next/Library/2025-03-13-20-48-58.gh-issue-123471.cM4w4f.rst
new file mode 100644
index 000000000000000..cfc783900de70fe
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-03-13-20-48-58.gh-issue-123471.cM4w4f.rst
@@ -0,0 +1 @@
+Make concurrent iterations over :class:`itertools.cycle` safe under free-threading.
diff --git a/Misc/NEWS.d/next/Library/2025-04-22-21-00-23.gh-issue-123471.asOLA2.rst b/Misc/NEWS.d/next/Library/2025-04-22-21-00-23.gh-issue-123471.asOLA2.rst
new file mode 100644
index 000000000000000..a4b4b6d2c23d495
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-04-22-21-00-23.gh-issue-123471.asOLA2.rst
@@ -0,0 +1 @@
+Make concurrent iterations over :class:`itertools.combinations` and :class:`itertools.product` safe under free-threading.
diff --git a/Misc/NEWS.d/next/Library/2025-06-18-19-25-32.gh-issue-123471.lx1Xbt.rst b/Misc/NEWS.d/next/Library/2025-06-18-19-25-32.gh-issue-123471.lx1Xbt.rst
new file mode 100644
index 000000000000000..6f395024a9e1790
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-06-18-19-25-32.gh-issue-123471.lx1Xbt.rst
@@ -0,0 +1 @@
+Make concurrent iterations over :class:`itertools.chain` safe under :term:`free threading`.
diff --git a/Misc/NEWS.d/next/Library/2026-02-03-08-50-58.gh-issue-123471.yF1Gym.rst b/Misc/NEWS.d/next/Library/2026-02-03-08-50-58.gh-issue-123471.yF1Gym.rst
new file mode 100644
index 000000000000000..85e9a03426e1fca
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-02-03-08-50-58.gh-issue-123471.yF1Gym.rst
@@ -0,0 +1 @@
+Make concurrent iteration over :class:`itertools.combinations_with_replacement` and :class:`itertools.permutations` safe under free-threading.
diff --git a/Misc/NEWS.d/next/Library/2026-02-04-20-30-59.gh-issue-123471.1dnPvs.rst b/Misc/NEWS.d/next/Library/2026-02-04-20-30-59.gh-issue-123471.1dnPvs.rst
new file mode 100644
index 000000000000000..d650103e28ee686
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-02-04-20-30-59.gh-issue-123471.1dnPvs.rst
@@ -0,0 +1 @@
+Make concurrent iteration over :class:`itertools.accumulate` safe under free-threading.
diff --git a/Misc/NEWS.d/next/Library/2026-03-17-19-51-05.gh-issue-123471.oY4UR5.rst b/Misc/NEWS.d/next/Library/2026-03-17-19-51-05.gh-issue-123471.oY4UR5.rst
new file mode 100644
index 000000000000000..8d2e1b970e81711
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-03-17-19-51-05.gh-issue-123471.oY4UR5.rst
@@ -0,0 +1 @@
+Make concurrent iteration over :class:`itertools.zip_longest` safe under free-threading.
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index ffe44595ac59e77..c307484d13377d4 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -1211,7 +1211,6 @@ typedef struct {
     PyObject *it;
     PyObject *saved;
     Py_ssize_t index;
-    int firstpass;
 } cycleobject;
 
 #define cycleobject_CAST(op)    ((cycleobject *)(op))
@@ -1252,8 +1251,7 @@ itertools_cycle_impl(PyTypeObject *type, PyObject *iterable)
     }
     lz->it = it;
     lz->saved = saved;
-    lz->index = 0;
-    lz->firstpass = 0;
+    lz->index = -1;
 
     return (PyObject *)lz;
 }
@@ -1286,11 +1284,11 @@ cycle_next(PyObject *op)
     cycleobject *lz = cycleobject_CAST(op);
     PyObject *item;
 
-    if (lz->it != NULL) {
+    Py_ssize_t index = FT_ATOMIC_LOAD_SSIZE_RELAXED(lz->index);
+
+    if (index < 0) {
         item = PyIter_Next(lz->it);
         if (item != NULL) {
-            if (lz->firstpass)
-                return item;
             if (PyList_Append(lz->saved, item)) {
                 Py_DECREF(item);
                 return NULL;
@@ -1300,15 +1298,22 @@ cycle_next(PyObject *op)
         /* Note:  StopIteration is already cleared by PyIter_Next() */
         if (PyErr_Occurred())
             return NULL;
+        index = 0;
+        FT_ATOMIC_STORE_SSIZE_RELAXED(lz->index, 0);
+#ifndef Py_GIL_DISABLED
         Py_CLEAR(lz->it);
+#endif
     }
     if (PyList_GET_SIZE(lz->saved) == 0)
         return NULL;
-    item = PyList_GET_ITEM(lz->saved, lz->index);
-    lz->index++;
-    if (lz->index >= PyList_GET_SIZE(lz->saved))
-        lz->index = 0;
-    return Py_NewRef(item);
+    item = PyList_GetItemRef(lz->saved, index);
+    assert(item);
+    index++;
+    if (index >= PyList_GET_SIZE(lz->saved)) {
+        index = 0;
+    }
+    FT_ATOMIC_STORE_SSIZE_RELAXED(lz->index, index);
+    return item;
 }
 
 static PyType_Slot cycle_slots[] = {
@@ -1962,8 +1967,8 @@ chain_traverse(PyObject *op, visitproc visit, void *arg)
     return 0;
 }
 
-static PyObject *
-chain_next(PyObject *op)
+static inline PyObject *
+chain_next_lock_held(PyObject *op)
 {
     chainobject *lz = chainobject_CAST(op);
     PyObject *item;
@@ -2001,6 +2006,16 @@ chain_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+chain_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = chain_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 PyDoc_STRVAR(chain_doc,
 "chain(*iterables)\n\
 --\n\
@@ -2172,7 +2187,7 @@ product_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-product_next(PyObject *op)
+product_next_lock_held(PyObject *op)
 {
     productobject *lz = productobject_CAST(op);
     PyObject *pool;
@@ -2258,6 +2273,16 @@ product_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+product_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = product_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef product_methods[] = {
     {"__sizeof__", product_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */
@@ -2405,7 +2430,7 @@ combinations_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-combinations_next(PyObject *op)
+combinations_next_lock_held(PyObject *op)
 {
     combinationsobject *co = combinationsobject_CAST(op);
     PyObject *elem;
@@ -2490,6 +2515,16 @@ combinations_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+combinations_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = combinations_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef combinations_methods[] = {
     {"__sizeof__", combinations_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */
@@ -2649,7 +2684,7 @@ cwr_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-cwr_next(PyObject *op)
+cwr_next_lock_held(PyObject *op)
 {
     cwrobject *co = cwrobject_CAST(op);
     PyObject *elem;
@@ -2728,6 +2763,16 @@ cwr_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+cwr_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = cwr_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef cwr_methods[] = {
     {"__sizeof__", cwr_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */
@@ -2908,7 +2953,7 @@ permutations_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-permutations_next(PyObject *op)
+permutations_next_lock_held(PyObject *op)
 {
     permutationsobject *po = permutationsobject_CAST(op);
     PyObject *elem;
@@ -2998,6 +3043,16 @@ permutations_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+permutations_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = permutations_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef permuations_methods[] = {
     {"__sizeof__", permutations_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */
@@ -3105,7 +3160,7 @@ accumulate_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-accumulate_next(PyObject *op)
+accumulate_next_lock_held(PyObject *op)
 {
     accumulateobject *lz = accumulateobject_CAST(op);
     PyObject *val, *newtotal;
@@ -3137,6 +3192,16 @@ accumulate_next(PyObject *op)
     return newtotal;
 }
 
+static PyObject *
+accumulate_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = accumulate_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyType_Slot accumulate_slots[] = {
     {Py_tp_dealloc, accumulate_dealloc},
     {Py_tp_getattro, PyObject_GenericGetAttr},
@@ -3895,7 +3960,7 @@ zip_longest_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-zip_longest_next(PyObject *op)
+zip_longest_next_lock_held(PyObject *op)
 {
     ziplongestobject *lz = ziplongestobject_CAST(op);
     Py_ssize_t i;
@@ -3966,6 +4031,16 @@ zip_longest_next(PyObject *op)
     return result;
 }
 
+static PyObject *
+zip_longest_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = zip_longest_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 PyDoc_STRVAR(zip_longest_doc,
 "zip_longest(*iterables, fillvalue=None)\n\
 --\n\