diff --git a/Doc/c-api/arg.rst b/Doc/c-api/arg.rst
index a878b20c928ea3d..0ebcfe38ae503ed 100644
--- a/Doc/c-api/arg.rst
+++ b/Doc/c-api/arg.rst
@@ -402,18 +402,33 @@ inside nested parentheses.  They are:
    For example, the format string ``"OO|OO"`` corresponds to the Python
    signature ``f(a, b, c=None, d=None)``.
 
+   :c:func:`PyArg_ParseTupleAndKeywords` only:
+   after ``%`` it indicates that the remaining keyword-only arguments are optional.
+
 ``$``
    :c:func:`PyArg_ParseTupleAndKeywords` only:
    Indicates that the remaining arguments in the Python argument list are
    keyword-only.
    They are optional if ``|`` was specified before ``$``, and required otherwise.
    ``|`` cannot be specified after ``$``.
+   Use ``%`` to mix required and optional keyword-only arguments.
    For example, the format string ``"O|O$O"`` corresponds to the Python
    signature ``f(a, b=None, *, c=None)``,
    and the format string ``"OO$OO"`` corresponds to ``f(a, b, *, c, d)``.
 
    .. versionadded:: 3.3
 
+``%``
+   :c:func:`PyArg_ParseTupleAndKeywords` only:
+   Indicates that the remaining arguments in the Python argument list are
+   keyword-only and required.
+   They become optional after ``|``.
+   Unlike ``$``, it does not depend on whether ``|`` was specified before it.
+   For example, the format string ``"O|O%O|O"`` corresponds to the Python
+   signature ``f(a, b=None, *, c, d=None)``.
+
+   .. versionadded:: next
+
 ``:``
    The list of format units ends here; the string after the colon is used as the
    function name in error messages (the "associated value" of the exception that
diff --git a/Doc/whatsnew/3.16.rst b/Doc/whatsnew/3.16.rst
index 210bcafe65f5e9c..373def6c92c519e 100644
--- a/Doc/whatsnew/3.16.rst
+++ b/Doc/whatsnew/3.16.rst
@@ -845,7 +845,13 @@ C API changes
 New features
 ------------
 
-* TODO
+* :c:func:`PyArg_ParseTupleAndKeywords` now supports required keyword-only
+  arguments mixed with optional arguments.
+  The new format unit ``%`` starts the keyword-only arguments which are
+  required until ``|``.
+  For example, the format string ``"O|O%O|O"`` corresponds to the Python
+  signature ``f(a, b=None, *, c, d=None)``.
+  (Contributed by Serhiy Storchaka in :gh:`78416`.)
 
 Porting to Python 3.16
 ----------------------
diff --git a/Include/cpython/modsupport.h b/Include/cpython/modsupport.h
index cfeee6e8ab3414d..4aef6252a843dc1 100644
--- a/Include/cpython/modsupport.h
+++ b/Include/cpython/modsupport.h
@@ -31,6 +31,7 @@ typedef struct _PyArg_Parser {
     int pos;                /* number of positional-only arguments */
     int min;                /* minimal number of arguments */
     int max;                /* maximal number of positional arguments */
+    int minkw;              /* index of the first optional keyword-only argument */
     PyObject *kwtuple;      /* tuple of keyword parameter names */
     struct _PyArg_Parser *next;
 } _PyArg_Parser;
diff --git a/Lib/test/test_capi/test_getargs.py b/Lib/test/test_capi/test_getargs.py
index bbc09e50eb8e450..12a086f08a2ca8f 100644
--- a/Lib/test/test_capi/test_getargs.py
+++ b/Lib/test/test_capi/test_getargs.py
@@ -1,6 +1,7 @@
 import string
 import sys
 import unittest
+from functools import partial
 from test import support
 from test.support import import_helper
 from test.support import script_helper
@@ -825,6 +826,80 @@ def __hash__(self):
             getargs_keyword_only(1, 2, **{BadStr("monster"): 666})
 
 
+class RequiredKeywordOnly_TestCase(unittest.TestCase):
+    # '%' marks the start of the keyword-only arguments, which are required
+    # until '|', so that required and optional ones can be mixed.
+
+    def parse(self, format, args, kwargs, keywords=('a', 'b', 'c', 'd')):
+        return _testcapi.parse_tuple_and_keywords(args, kwargs,
+                                                  format, list(keywords))
+
+    def test_required_after_optional(self):
+        # f(a, b=None, *, c, d=None)
+        parse = partial(self.parse, "O|O%O|O")
+        self.assertEqual(parse((1, 2), {'c': 3, 'd': 4}), (1, 2, 3, 4))
+        self.assertEqual(parse((1,), {'c': 3}), (1, None, 3, None))
+        with self.assertRaisesRegex(TypeError, "missing required argument 'c'"):
+            parse((1,), {})
+        with self.assertRaisesRegex(TypeError, "missing required argument 'c'"):
+            parse((1,), {'d': 4})
+        with self.assertRaisesRegex(TypeError, "at most 2 positional"):
+            parse((1, 2, 3), {'c': 3})
+
+    def test_all_keyword_only_required(self):
+        # f(a, b=None, *, c, d)
+        parse = partial(self.parse, "O|O%OO")
+        self.assertEqual(parse((1,), {'c': 3, 'd': 4}), (1, None, 3, 4))
+        with self.assertRaisesRegex(TypeError, "missing required argument 'd'"):
+            parse((1,), {'c': 3})
+
+    def test_all_positional_required(self):
+        # f(a, b, *, c, d=None)
+        parse = partial(self.parse, "OO%O|O")
+        self.assertEqual(parse((1, 2), {'c': 3}), (1, 2, 3, None))
+        with self.assertRaisesRegex(TypeError, "missing required argument 'c'"):
+            parse((1, 2), {})
+
+    def test_cached_parser(self):
+        # The same format, parsed once and cached in a _PyArg_Parser.
+        f = _testcapi.getargs_fast_required_kwonly
+        self.assertEqual(f(1, 2, c=3, d=4), (1, 2, 3, 4))
+        self.assertEqual(f(1, c=3), (1, None, 3, None))
+        with self.assertRaisesRegex(TypeError, "missing required argument 'c'"):
+            f(1)
+        with self.assertRaisesRegex(TypeError, "missing required argument 'c'"):
+            f(1, d=4)
+
+    def test_invalid_format(self):
+        for format, msg in (
+            ("O%O%O", r"\$ specified twice"),
+            ("O%O$O", r"\$ specified twice"),
+            ("O%O|O|O", r"\| specified twice"),
+            ("O$O|O", r"\$ before \|"),
+        ):
+            with self.subTest(format=format):
+                n = format.count('O')
+                npos = len(format) - len(format.lstrip('O'))
+                args = tuple(range(npos))
+                kwargs = {'abcd'[i]: i for i in range(npos, n)}
+                with self.assertRaisesRegex(SystemError, msg):
+                    self.parse(format, args, kwargs, 'abcd'[:n])
+
+    def test_unchanged_meaning_of_dollar(self):
+        # '$' still inherits the state of the positional arguments.
+        parse = partial(self.parse, "O|O$O", keywords=('a', 'b', 'c'))
+        self.assertEqual(parse((1,), {}), (1, None, None))
+        parse = partial(self.parse, "OO$O", keywords=('a', 'b', 'c'))
+        self.assertEqual(parse((1, 2), {'c': 3}), (1, 2, 3))
+        with self.assertRaisesRegex(TypeError, "missing required argument 'c'"):
+            parse((1, 2), {})
+        # The same with a cached parser.
+        f = _testcapi.getargs_fast_kwonly
+        self.assertEqual(f(1, 2, c=3, d=4), (1, 2, 3, 4))
+        with self.assertRaisesRegex(TypeError, "missing required argument 'c'"):
+            f(1, 2)
+
+
 class PositionalOnlyAndKeywords_TestCase(unittest.TestCase):
     from _testcapi import getargs_positional_only_and_keywords as getargs
 
@@ -1164,8 +1239,8 @@ def test_skipitem(self):
 
             # skip parentheses, the error reporting is inconsistent about them
             # skip 'e' and 'w', they're always two-character codes
-            # skip '|' and '$', they don't represent arguments anyway
-            if c in '()ew|$':
+            # skip '|', '$' and '%', they don't represent arguments anyway
+            if c in '()ew|$%':
                 continue
 
             # test the format unit when not skipped
diff --git a/Lib/test/test_clinic.py b/Lib/test/test_clinic.py
index 1dc1c4eaaaba196..6fce724ec2e0e9a 100644
--- a/Lib/test/test_clinic.py
+++ b/Lib/test/test_clinic.py
@@ -2207,6 +2207,36 @@ def test_depr_slash_duplicate2(self):
         err = "Function 'bar': '/ [from 3.14]' must precede '/ [from 3.15]'"
         self.expect_failure(block, err, lineno=5)
 
+    def test_required_keyword_only_after_optional(self):
+        function = self.parse_function("""
+            module foo
+            foo.bar
+                a: int
+                b: int = 0
+                *
+                c: int
+                d: int = 0
+            Docstring.
+        """)
+        _, a, b, c, d = function.parameters.values()
+        self.assertFalse(a.converter.is_optional())
+        self.assertTrue(b.converter.is_optional())
+        self.assertFalse(c.converter.is_optional())
+        self.assertTrue(d.converter.is_optional())
+
+    def test_optional_before_required_keyword_only(self):
+        block = """
+            module foo
+            foo.bar
+                *
+                a: int = 0
+                b: int
+            Docstring.
+        """
+        err = ("Can't have a parameter without a default ('b') "
+               "after a parameter with a default!")
+        self.expect_failure(block, err, lineno=4)
+
     def test_single_slash(self):
         block = """
             module foo
@@ -4664,6 +4694,41 @@ def test_limited_capi_float(self):
         self.assertIn("float f;", generated)
         self.assertIn("f = (float) PyFloat_AsDouble", generated)
 
+    def test_limited_capi_required_keyword_only(self):
+        block = self.wrap_clinic_input("""
+            func
+                a: object
+                b: object = None
+                *
+                c: object
+                d: object = None
+        """)
+        generated = self.clinic.parse(block)
+        # '$' cannot express this, only '%' can.
+        self.assertIn('"O|O%O|O:func"', generated)
+
+    def test_limited_capi_optional_after_required_keyword_only(self):
+        block = self.wrap_clinic_input("""
+            func
+                a: object
+                *
+                b: object
+                c: object = None
+        """)
+        generated = self.clinic.parse(block)
+        self.assertIn('"O%O|O:func"', generated)
+
+    def test_limited_capi_keyword_only(self):
+        # '$' is still used if it can express the signature.
+        block = self.wrap_clinic_input("""
+            func
+                a: object
+                *
+                b: object
+        """)
+        generated = self.clinic.parse(block)
+        self.assertIn('"O$O:func"', generated)
+
     def test_limited_capi_double(self):
         block = self.wrap_clinic_input("""
             func
@@ -4720,6 +4785,18 @@ def test_my_double_sum(self):
                 with self.assertRaises(TypeError):
                     func(1., "2")
 
+    def test_required_kwonly(self):
+        # test a required keyword-only parameter after an optional one
+        func = _testclinic_limited.required_kwonly
+        self.assertEqual(func(1, 2, c=3, d=4), (1, 2, 3, 4))
+        self.assertEqual(func(1, c=3), (1, None, 3, None))
+        with self.assertRaisesRegex(TypeError, "argument 'c'"):
+            func(1, 2)
+        with self.assertRaisesRegex(TypeError, "argument 'c'"):
+            func(1, 2, d=4)
+        with self.assertRaises(TypeError):
+            func(1, 2, 3)
+
     def test_get_file_descriptor(self):
         # test 'file descriptor' converter: call PyObject_AsFileDescriptor()
         get_fd = _testclinic_limited.get_file_descriptor
diff --git a/Misc/NEWS.d/next/C_API/2026-08-06-17-11-54.gh-issue-78416.jsJUNi.rst b/Misc/NEWS.d/next/C_API/2026-08-06-17-11-54.gh-issue-78416.jsJUNi.rst
new file mode 100644
index 000000000000000..3baf1dbd651797e
--- /dev/null
+++ b/Misc/NEWS.d/next/C_API/2026-08-06-17-11-54.gh-issue-78416.jsJUNi.rst
@@ -0,0 +1,3 @@
+:c:func:`PyArg_ParseTupleAndKeywords` now supports required keyword-only arguments mixed with optional arguments.
+The new format unit ``%`` starts the keyword-only arguments which are required until ``|``.
+For example, the format string ``"O|O%O|O"`` corresponds to the Python signature ``f(a, b=None, *, c, d=None)``.
diff --git a/Modules/_testcapi/getargs.c b/Modules/_testcapi/getargs.c
index ee04c760d272132..db1a110fee4e6c8 100644
--- a/Modules/_testcapi/getargs.c
+++ b/Modules/_testcapi/getargs.c
@@ -765,6 +765,42 @@ gh_99240_clear_args(PyObject *self, PyObject *args)
     Py_RETURN_NONE;
 }
 
+/* f(a, b=None, *, c, d=None) parsed with a cached _PyArg_Parser. */
+static PyObject *
+getargs_fast_required_kwonly(PyObject *self, PyObject *args, PyObject *kwargs)
+{
+    static const char * const keywords[] = {"a", "b", "c", "d", NULL};
+    static _PyArg_Parser parser = {
+        .format = "O|O%O|O:getargs_fast_required_kwonly",
+        .keywords = keywords,
+    };
+    PyObject *a, *b = Py_None, *c, *d = Py_None;
+    if (!_PyArg_ParseTupleAndKeywordsFast(args, kwargs, &parser,
+                                          &a, &b, &c, &d))
+    {
+        return NULL;
+    }
+    return Py_BuildValue("OOOO", a, b, c, d);
+}
+
+/* f(a, b, *, c, d) parsed with a cached _PyArg_Parser. */
+static PyObject *
+getargs_fast_kwonly(PyObject *self, PyObject *args, PyObject *kwargs)
+{
+    static const char * const keywords[] = {"a", "b", "c", "d", NULL};
+    static _PyArg_Parser parser = {
+        .format = "OO$OO:getargs_fast_kwonly",
+        .keywords = keywords,
+    };
+    PyObject *a, *b, *c, *d;
+    if (!_PyArg_ParseTupleAndKeywordsFast(args, kwargs, &parser,
+                                          &a, &b, &c, &d))
+    {
+        return NULL;
+    }
+    return Py_BuildValue("OOOO", a, b, c, d);
+}
+
 static PyMethodDef test_methods[] = {
     {"get_args",                get_args,                        METH_VARARGS},
     {"get_kwargs", _PyCFunction_CAST(get_kwargs), METH_VARARGS|METH_KEYWORDS},
@@ -809,6 +845,10 @@ static PyMethodDef test_methods[] = {
     {"getargs_z_hash",          getargs_z_hash,                  METH_VARARGS},
     {"getargs_z_star",          getargs_z_star,                  METH_VARARGS},
     {"parse_tuple_and_keywords", parse_tuple_and_keywords,       METH_VARARGS},
+    {"getargs_fast_required_kwonly",
+     _PyCFunction_CAST(getargs_fast_required_kwonly), METH_VARARGS|METH_KEYWORDS},
+    {"getargs_fast_kwonly", _PyCFunction_CAST(getargs_fast_kwonly),
+                                                 METH_VARARGS|METH_KEYWORDS},
     {"gh_99240_clear_args",     gh_99240_clear_args,             METH_VARARGS},
     {"test_w_code_invalid",     test_w_code_invalid,             METH_NOARGS},
     {NULL},
diff --git a/Modules/_testclinic_limited.c b/Modules/_testclinic_limited.c
index 370433b3e2a0d94..f141499ad007f08 100644
--- a/Modules/_testclinic_limited.c
+++ b/Modules/_testclinic_limited.c
@@ -129,9 +129,31 @@ static PyMethodDef tester_methods[] = {
     MY_FLOAT_SUM_METHODDEF
     MY_DOUBLE_SUM_METHODDEF
     GET_FILE_DESCRIPTOR_METHODDEF
+    REQUIRED_KWONLY_METHODDEF
     {NULL, NULL}
 };
 
+/*[clinic input]
+required_kwonly
+
+    a: object
+    b: object = None
+    *
+    c: object
+    d: object = None
+
+Mix an optional parameter with a required keyword-only one.
+[clinic start generated code]*/
+
+static PyObject *
+required_kwonly_impl(PyObject *module, PyObject *a, PyObject *b, PyObject *c,
+                     PyObject *d)
+/*[clinic end generated code: output=8e9a974afa614cd6 input=297ec6487f6373dd]*/
+{
+    return Py_BuildValue("OOOO", a, b, c, d);
+}
+
+
 static struct PyModuleDef _testclinic_module = {
     PyModuleDef_HEAD_INIT,
     .m_name = "_testclinic_limited",
diff --git a/Modules/clinic/_testclinic_limited.c.h b/Modules/clinic/_testclinic_limited.c.h
index 94897f4c6dc4276..8105a7bde409c7f 100644
--- a/Modules/clinic/_testclinic_limited.c.h
+++ b/Modules/clinic/_testclinic_limited.c.h
@@ -206,4 +206,36 @@ get_file_descriptor(PyObject *module, PyObject *arg)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=03fd7811c056dc74 input=a9049054013a1b77]*/
+
+PyDoc_STRVAR(required_kwonly__doc__,
+"required_kwonly($module, /, a, b=None, *, c, d=None)\n"
+"--\n"
+"\n"
+"Mix an optional parameter with a required keyword-only one.");
+
+#define REQUIRED_KWONLY_METHODDEF    \
+    {"required_kwonly", (PyCFunction)(void(*)(void))required_kwonly, METH_VARARGS|METH_KEYWORDS, required_kwonly__doc__},
+
+static PyObject *
+required_kwonly_impl(PyObject *module, PyObject *a, PyObject *b, PyObject *c,
+                     PyObject *d);
+
+static PyObject *
+required_kwonly(PyObject *module, PyObject *args, PyObject *kwargs)
+{
+    PyObject *return_value = NULL;
+    static char *_keywords[] = {"a", "b", "c", "d", NULL};
+    PyObject *a;
+    PyObject *b = Py_None;
+    PyObject *c;
+    PyObject *d = Py_None;
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwargs, "O|O%O|O:required_kwonly", _keywords,
+        &a, &b, &c, &d))
+        goto exit;
+    return_value = required_kwonly_impl(module, a, b, c, d);
+
+exit:
+    return return_value;
+}
+/*[clinic end generated code: output=1e9068892aedbdce input=a9049054013a1b77]*/
diff --git a/Python/getargs.c b/Python/getargs.c
index 3f423266bff7f47..7cc7efc77e683ba 100644
--- a/Python/getargs.c
+++ b/Python/getargs.c
@@ -1680,6 +1680,9 @@ vgetargskeywords_impl(PyObject *const *args, Py_ssize_t nargs,
     const char *fname, *msg, *custom_msg;
     int min = INT_MAX;
     int max = INT_MAX;
+    /* The index of the first optional keyword-only argument. */
+    int minkw = INT_MAX;
+    char kwonly_marker = 0;
     int i, pos, len;
     int skip = 0;
     Py_ssize_t nkwargs;
@@ -1758,22 +1761,23 @@ vgetargskeywords_impl(PyObject *const *args, Py_ssize_t nargs,
     /* convert tuple args and keyword args in same loop, using kwlist to drive process */
     for (i = 0; i < len; i++) {
         if (*format == '|') {
-            if (min != INT_MAX) {
+            if (kwonly_marker == '$') {
                 PyErr_SetString(PyExc_SystemError,
-                                "Invalid format string (| specified twice)");
+                                "Invalid format string ($ before |)");
                 return cleanreturn(0, &freelist);
             }
-
-            min = i;
-            format++;
-
-            if (max != INT_MAX) {
+            /* The optional arguments start here: the positional ones before
+               '%', the keyword-only ones after it. */
+            int *popt = kwonly_marker ? &minkw : &min;
+            if (*popt != INT_MAX) {
                 PyErr_SetString(PyExc_SystemError,
-                                "Invalid format string ($ before |)");
+                                "Invalid format string (| specified twice)");
                 return cleanreturn(0, &freelist);
             }
+            *popt = i;
+            format++;
         }
-        if (*format == '$') {
+        if (*format == '$' || *format == '%') {
             if (max != INT_MAX) {
                 PyErr_SetString(PyExc_SystemError,
                                 "Invalid format string ($ specified twice)");
@@ -1781,6 +1785,10 @@ vgetargskeywords_impl(PyObject *const *args, Py_ssize_t nargs,
             }
 
             max = i;
+            kwonly_marker = *format;
+            /* '$' inherits the state of the positional arguments,
+               '%' starts with required arguments. */
+            minkw = (kwonly_marker == '$') ? min : INT_MAX;
             format++;
 
             if (max < pos) {
@@ -1854,7 +1862,7 @@ vgetargskeywords_impl(PyObject *const *args, Py_ssize_t nargs,
                 continue;
             }
 
-            if (i < min) {
+            if (i < (i < max ? min : minkw)) {
                 if (i < pos) {
                     assert (min == INT_MAX);
                     assert (max == INT_MAX);
@@ -1877,7 +1885,9 @@ vgetargskeywords_impl(PyObject *const *args, Py_ssize_t nargs,
              * fulfilled and no keyword args left, with no further
              * validation. XXX Maybe skip this in debug build ?
              */
-            if (!nkwargs && !skip) {
+            if (!nkwargs && !skip &&
+                (i >= minkw || strchr(format, '%') == NULL))
+            {
                 return cleanreturn(1, &freelist);
             }
         }
@@ -1905,7 +1915,9 @@ vgetargskeywords_impl(PyObject *const *args, Py_ssize_t nargs,
         return cleanreturn(0, &freelist);
     }
 
-    if (!IS_END_OF_FORMAT(*format) && (*format != '|') && (*format != '$')) {
+    if (!IS_END_OF_FORMAT(*format) && (*format != '|') && (*format != '$') &&
+        (*format != '%'))
+    {
         PyErr_Format(PyExc_SystemError,
             "more argument specifiers than keyword list entries "
             "(remaining format:'%s')", format);
@@ -2046,7 +2058,7 @@ scan_keywords(const char * const *keywords, int *ptotal, int *pposonly)
 static int
 parse_format(const char *format, int total, int npos,
              const char **pfname, const char **pcustommsg,
-             int *pmin, int *pmax)
+             int *pmin, int *pmax, int *pminkw)
 {
     /* grab the function name or custom error msg first (mutually exclusive) */
     const char *custommsg;
@@ -2064,22 +2076,28 @@ parse_format(const char *format, int total, int npos,
 
     int min = INT_MAX;
     int max = INT_MAX;
+    /* The index of the first optional keyword-only argument. */
+    int minkw = INT_MAX;
+    char kwonly_marker = 0;
     for (int i = 0; i < total; i++) {
         if (*format == '|') {
-            if (min != INT_MAX) {
+            if (kwonly_marker == '$') {
                 PyErr_SetString(PyExc_SystemError,
-                                "Invalid format string (| specified twice)");
+                                "Invalid format string ($ before |)");
                 return -1;
             }
-            if (max != INT_MAX) {
+            /* The optional arguments start here: the positional ones before
+               '%', the keyword-only ones after it. */
+            int *popt = kwonly_marker ? &minkw : &min;
+            if (*popt != INT_MAX) {
                 PyErr_SetString(PyExc_SystemError,
-                                "Invalid format string ($ before |)");
+                                "Invalid format string (| specified twice)");
                 return -1;
             }
-            min = i;
+            *popt = i;
             format++;
         }
-        if (*format == '$') {
+        if (*format == '$' || *format == '%') {
             if (max != INT_MAX) {
                 PyErr_SetString(PyExc_SystemError,
                                 "Invalid format string ($ specified twice)");
@@ -2091,6 +2109,10 @@ parse_format(const char *format, int total, int npos,
                 return -1;
             }
             max = i;
+            kwonly_marker = *format;
+            /* '$' inherits the state of the positional arguments,
+               '%' starts with required arguments. */
+            minkw = (kwonly_marker == '$') ? min : INT_MAX;
             format++;
         }
         if (IS_END_OF_FORMAT(*format)) {
@@ -2107,6 +2129,8 @@ parse_format(const char *format, int total, int npos,
             return -1;
         }
     }
+    /* Without a marker the optional arguments are not keyword-only. */
+    minkw = Py_MIN((max == INT_MAX) ? min : minkw, total);
     min = Py_MIN(min, total);
     max = Py_MIN(max, total);
 
@@ -2121,6 +2145,7 @@ parse_format(const char *format, int total, int npos,
     *pcustommsg = custommsg;
     *pmin = min;
     *pmax = max;
+    *pminkw = minkw;
     return 0;
 }
 
@@ -2164,11 +2189,11 @@ _parser_init(void *arg)
     }
 
     const char *fname, *custommsg = NULL;
-    int min = 0, max = 0;
+    int min = 0, max = 0, minkw = 0;
     if (parser->format) {
         assert(parser->fname == NULL);
         if (parse_format(parser->format, len, pos,
-                         &fname, &custommsg, &min, &max) < 0) {
+                         &fname, &custommsg, &min, &max, &minkw) < 0) {
             return -1;
         }
     }
@@ -2211,6 +2236,7 @@ _parser_init(void *arg)
     parser->custom_msg = custommsg;
     parser->min = min;
     parser->max = max;
+    parser->minkw = minkw;
     parser->kwtuple = kwtuple;
     parser->is_kwtuple_owned = owned;
 
@@ -2380,7 +2406,11 @@ vgetargskeywordsfast_impl(PyObject *const *args, Py_ssize_t nargs,
         if (*format == '|') {
             format++;
         }
-        if (*format == '$') {
+        if (*format == '$' || *format == '%') {
+            format++;
+        }
+        if (*format == '|') {
+            /* optional keyword-only arguments after '%' */
             format++;
         }
         assert(!IS_END_OF_FORMAT(*format));
@@ -2418,7 +2448,7 @@ vgetargskeywordsfast_impl(PyObject *const *args, Py_ssize_t nargs,
             continue;
         }
 
-        if (i < parser->min) {
+        if (i < (i < parser->max ? parser->min : parser->minkw)) {
             /* Less arguments than required */
             if (i < pos) {
                 int min = Py_MIN(pos, parser->min);
@@ -2446,7 +2476,7 @@ vgetargskeywordsfast_impl(PyObject *const *args, Py_ssize_t nargs,
          * fulfilled and no keyword args left, with no further
          * validation. XXX Maybe skip this in debug build ?
          */
-        if (!nkwargs) {
+        if (!nkwargs && i >= parser->minkw) {
             return cleanreturn(1, &freelist);
         }
 
diff --git a/Tools/c-analyzer/cpython/ignored.tsv b/Tools/c-analyzer/cpython/ignored.tsv
index 4c143164650a2ba..50c9967db33a195 100644
--- a/Tools/c-analyzer/cpython/ignored.tsv
+++ b/Tools/c-analyzer/cpython/ignored.tsv
@@ -785,6 +785,7 @@ Modules/_zstd/_zstdmodule.c	-	_zstdmodule	-
 Modules/clinic/md5module.c.h	_md5_md5	_keywords	-
 Modules/clinic/grpmodule.c.h	grp_getgrgid	_keywords	-
 Modules/clinic/grpmodule.c.h	grp_getgrnam	_keywords	-
+Modules/clinic/_testclinic_limited.c.h	required_kwonly	_keywords	-
 Objects/object.c	-	constants	static PyObject*[]
 Objects/dictobject.c	-	PyFrozenDict_Type	-
 
diff --git a/Tools/clinic/libclinic/codegen.py b/Tools/clinic/libclinic/codegen.py
index b2f1db6f8ef8da7..556b839f24e4ec0 100644
--- a/Tools/clinic/libclinic/codegen.py
+++ b/Tools/clinic/libclinic/codegen.py
@@ -38,6 +38,11 @@ def __init__(self) -> None:
         # Should be individual strings that will get
         self.format_units: list[str] = []
 
+        # The marker which starts the keyword-only parameters,
+        # and whether the optional ones already started.
+        self.kwonly_marker = ''
+        self.kwonly_optional = False
+
         # The varargs arguments for PyArg_ParseTuple.
         self.parse_arguments: list[str] = []
 
diff --git a/Tools/clinic/libclinic/converter.py b/Tools/clinic/libclinic/converter.py
index c10235237d4b716..6469712eaf948f7 100644
--- a/Tools/clinic/libclinic/converter.py
+++ b/Tools/clinic/libclinic/converter.py
@@ -327,10 +327,31 @@ def _render_non_self(
             data.keywords.append(parameter.name)
 
         # format_units
-        if self.is_optional() and '|' not in data.format_units:
+        if not parameter.is_keyword_only():
+            if self.is_optional() and '|' not in data.format_units:
+                data.format_units.append('|')
+        elif not data.kwonly_marker:
+            # The first keyword-only parameter.  '$' only inherits the
+            # state of the positional parameters, '%' sets its own.
+            if self.is_optional():
+                if '|' not in data.format_units:
+                    data.format_units.append('|')
+                data.kwonly_marker = '$'
+                data.kwonly_optional = True
+            elif ('|' in data.format_units
+                  or any(p.converter.is_optional()
+                         for p in parameter.function.render_parameters
+                         if p.is_keyword_only())):
+                # Required before or after an optional parameter:
+                # only '%' can express this.
+                data.kwonly_marker = '%'
+            else:
+                data.kwonly_marker = '$'
+            data.format_units.append(data.kwonly_marker)
+        elif self.is_optional() and not data.kwonly_optional:
+            # The first optional keyword-only parameter after '%'.
+            data.kwonly_optional = True
             data.format_units.append('|')
-        if parameter.is_keyword_only() and '$' not in data.format_units:
-            data.format_units.append('$')
         data.format_units.append(self.format_unit)
 
         # parse_arguments
diff --git a/Tools/clinic/libclinic/dsl_parser.py b/Tools/clinic/libclinic/dsl_parser.py
index 4dcbc815cc6f25b..824388bdd79a52e 100644
--- a/Tools/clinic/libclinic/dsl_parser.py
+++ b/Tools/clinic/libclinic/dsl_parser.py
@@ -1179,6 +1179,10 @@ def parse_star(self, function: Function, version: VersionTuple | None) -> None:
             self.check_previous_star()
             self.check_remaining_star()
             self.keyword_only = True
+            # A keyword-only parameter can be required even if
+            # a positional one is optional.
+            if self.parameter_state is ParamState.OPTIONAL:
+                self.parameter_state = ParamState.REQUIRED
         else:
             if self.keyword_only:
                 fail(f"Function {function.name!r}: '* [from ...]' must precede '*'")
diff --git a/Tools/clinic/libclinic/parse_args.py b/Tools/clinic/libclinic/parse_args.py
index 2ad1e94ea2b4c79..e8e570d63bb028d 100644
--- a/Tools/clinic/libclinic/parse_args.py
+++ b/Tools/clinic/libclinic/parse_args.py
@@ -341,8 +341,6 @@ def init_limited_capi(self) -> None:
         self.limited_capi = self.codegen.limited_capi
         if self.limited_capi and (
                 (self.varpos and self.pos_only < len(self.parameters)) or
-                (any(p.is_optional() for p in self.parameters) and
-                 any(p.is_keyword_only() and not p.is_optional() for p in self.parameters)) or
                 any(c.broken_limited_capi for c in self.converters)):
             warn(f"Function {self.func.full_name} cannot use limited C API")
             self.limited_capi = False