diff --git a/Include/cpython/initconfig.h b/Include/cpython/initconfig.h
index c6057a4c3ed945..781007f787ef8e 100644
--- a/Include/cpython/initconfig.h
+++ b/Include/cpython/initconfig.h
@@ -212,10 +212,6 @@ typedef struct PyConfig {
     // If equal to 0, stop Python initialization before the "main" phase.
     int _init_main;
 
-    // If non-zero, disallow threads, subprocesses, and fork.
-    // Default: 0.
-    int _isolated_interpreter;
-
     // If non-zero, we believe we're running from a source tree.
     int _is_python_build;
 } PyConfig;
@@ -243,6 +239,16 @@ PyAPI_FUNC(PyStatus) PyConfig_SetWideStringList(PyConfig *config,
     PyWideStringList *list,
     Py_ssize_t length, wchar_t **items);
 
+typedef struct {
+    /* Allow forking the process. */
+    unsigned int allow_fork:1;
+    /* Allow creating subprocesses. */
+    unsigned int allow_subprocess:1;
+    /* Allow the creation of threads. */
+    unsigned int allow_threading:1;
+    /* Padding to ensure byte alignment. */
+    unsigned int :5;
+} _PyInterpreterConfig;
 
 /* --- Helper functions --------------------------------------- */
 
diff --git a/Include/cpython/pylifecycle.h b/Include/cpython/pylifecycle.h
index bb5b07ef5901c8..ec50d31842f6b2 100644
--- a/Include/cpython/pylifecycle.h
+++ b/Include/cpython/pylifecycle.h
@@ -62,4 +62,4 @@ PyAPI_FUNC(int) _Py_CoerceLegacyLocale(int warn);
 PyAPI_FUNC(int) _Py_LegacyLocaleDetected(int warn);
 PyAPI_FUNC(char *) _Py_SetLocaleFromEnv(int category);
 
-PyAPI_FUNC(PyThreadState *) _Py_NewInterpreter(int isolated_subinterpreter);
+PyAPI_FUNC(PyThreadState *) _Py_NewInterpreter(const _PyInterpreterConfig *);
diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index cc3c3eae941933..2cec5cbe17261a 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -269,7 +269,14 @@ PyAPI_FUNC(void) _PyInterpreterState_SetEvalFrameFunc(
     PyInterpreterState *interp,
     _PyFrameEvalFunction eval_frame);
 
-PyAPI_FUNC(const PyConfig*) _PyInterpreterState_GetConfig(PyInterpreterState *interp);
+PyAPI_FUNC(const _PyInterpreterConfig*) _PyInterpreterState_GetConfig(
+        PyInterpreterState *interp);
+
+PyAPI_FUNC(const PyConfig*) _PyInterpreterState_GetGlobalConfig(PyInterpreterState *interp);
+
+// Get the configuration of the current interpreter.
+// The caller must hold the GIL.
+PyAPI_FUNC(const PyConfig*) _Py_GetConfig(void);
 
 /* Get a copy of the current interpreter configuration.
 
@@ -283,8 +290,7 @@ PyAPI_FUNC(const PyConfig*) _PyInterpreterState_GetConfig(PyInterpreterState *in
 
    Once done with the configuration, PyConfig_Clear() must be called to clear
    it. */
-PyAPI_FUNC(int) _PyInterpreterState_GetConfigCopy(
-    struct PyConfig *config);
+PyAPI_FUNC(int) _Py_CopyConfig(PyConfig *config);
 
 /* Set the configuration of the current interpreter.
 
@@ -300,13 +306,8 @@ PyAPI_FUNC(int) _PyInterpreterState_GetConfigCopy(
 
    Return 0 on success. Raise an exception and return -1 on error.
 
-   The configuration should come from _PyInterpreterState_GetConfigCopy(). */
-PyAPI_FUNC(int) _PyInterpreterState_SetConfig(
-    const struct PyConfig *config);
-
-// Get the configuration of the current interpreter.
-// The caller must hold the GIL.
-PyAPI_FUNC(const PyConfig*) _Py_GetConfig(void);
+   The configuration should come from _Py_CopyConfig(). */
+PyAPI_FUNC(int) _Py_SetConfig(const PyConfig *config);
 
 
 /* cross-interpreter data */
diff --git a/Include/internal/pycore_initconfig.h b/Include/internal/pycore_initconfig.h
index 6e491261d55ca6..2114bc4db5fa55 100644
--- a/Include/internal/pycore_initconfig.h
+++ b/Include/internal/pycore_initconfig.h
@@ -166,6 +166,11 @@ extern PyStatus _PyConfig_SetPyArgv(
 PyAPI_FUNC(PyObject*) _PyConfig_AsDict(const PyConfig *config);
 PyAPI_FUNC(int) _PyConfig_FromDict(PyConfig *config, PyObject *dict);
 
+extern void _PyInterpreterConfig_Clear(_PyInterpreterConfig *);
+extern PyStatus _PyInterpreterConfig_Copy(
+    _PyInterpreterConfig *config,
+    const _PyInterpreterConfig *config2);
+
 extern void _Py_DumpPathConfig(PyThreadState *tstate);
 
 PyAPI_FUNC(PyObject*) _Py_Get_Getpath_CodeObject(void);
diff --git a/Include/internal/pycore_interp.h b/Include/internal/pycore_interp.h
index e7f914ec2fe521..e85594e86ac116 100644
--- a/Include/internal/pycore_interp.h
+++ b/Include/internal/pycore_interp.h
@@ -132,7 +132,8 @@ struct _is {
     PyObject *codec_error_registry;
     int codecs_initialized;
 
-    PyConfig config;
+    _PyInterpreterConfig config;
+
 #ifdef HAVE_DLOPEN
     int dlopenflags;
 #endif
diff --git a/Include/internal/pycore_pystate.h b/Include/internal/pycore_pystate.h
index 3d6d400f74dd1d..6c9d3e4d456f4d 100644
--- a/Include/internal/pycore_pystate.h
+++ b/Include/internal/pycore_pystate.h
@@ -41,7 +41,7 @@ _Py_GetMainConfig(void)
     if (interp == NULL) {
         return NULL;
     }
-    return _PyInterpreterState_GetConfig(interp);
+    return _PyInterpreterState_GetGlobalConfig(interp);
 }
 
 
diff --git a/Include/internal/pycore_runtime.h b/Include/internal/pycore_runtime.h
index 2c04ead45869fc..3f9f6e092ecc97 100644
--- a/Include/internal/pycore_runtime.h
+++ b/Include/internal/pycore_runtime.h
@@ -120,6 +120,7 @@ typedef struct pyruntimestate {
     struct _getargs_runtime_state getargs;
 
     PyPreConfig preconfig;
+    PyConfig config;
 
     // Audit values must be preserved when Py_Initialize()/Py_Finalize()
     // is called multiple times.
diff --git a/Include/internal/pycore_runtime_init.h b/Include/internal/pycore_runtime_init.h
index 621d5cc864255d..d8b2ddfaafa2f1 100644
--- a/Include/internal/pycore_runtime_init.h
+++ b/Include/internal/pycore_runtime_init.h
@@ -63,6 +63,11 @@ extern "C" {
             }, \
         }, \
         ._initial_thread = _PyThreadState_INIT, \
+        .config = { \
+            .allow_fork = 1, \
+            .allow_subprocess = 1, \
+            .allow_threading = 1, \
+        }, \
     }
 
 #define _PyThreadState_INIT \
diff --git a/Lib/test/_test_embed_set_config.py b/Lib/test/_test_embed_set_config.py
index 7ff641b37bf188..0c016b5d75d734 100644
--- a/Lib/test/_test_embed_set_config.py
+++ b/Lib/test/_test_embed_set_config.py
@@ -84,7 +84,6 @@ def test_set_invalid(self):
             'skip_source_first_line',
             '_install_importlib',
             '_init_main',
-            '_isolated_interpreter',
         ]
         if MS_WINDOWS:
             options.append('legacy_windows_stdio')
diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index 70d7367ea9e64f..afcbcc0f496109 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -495,7 +495,6 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         'check_hash_pycs_mode': 'default',
         'pathconfig_warnings': 1,
         '_init_main': 1,
-        '_isolated_interpreter': 0,
         'use_frozen_modules': not support.Py_DEBUG,
         'safe_path': 0,
         '_is_python_build': IGNORE_CONFIG,
@@ -879,8 +878,6 @@ def test_init_from_config(self):
 
             'check_hash_pycs_mode': 'always',
             'pathconfig_warnings': 0,
-
-            '_isolated_interpreter': 1,
         }
         self.check_all_configs("test_init_from_config", config, preconfig,
                                api=API_COMPAT)
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 38ef24637b7318..08bf345ead73c6 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -474,7 +474,7 @@ _io_text_encoding_impl(PyObject *module, PyObject *encoding, int stacklevel)
 {
     if (encoding == NULL || encoding == Py_None) {
         PyInterpreterState *interp = _PyInterpreterState_GET();
-        if (_PyInterpreterState_GetConfig(interp)->warn_default_encoding) {
+        if (_PyInterpreterState_GetGlobalConfig(interp)->warn_default_encoding) {
             if (PyErr_WarnEx(PyExc_EncodingWarning,
                              "'encoding' argument not specified", stacklevel)) {
                 return NULL;
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index 3369694653fd96..d90f891736b5b5 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -979,7 +979,7 @@ io_check_errors(PyObject *errors)
     PyInterpreterState *interp = _PyInterpreterState_GET();
 #ifndef Py_DEBUG
     /* In release mode, only check in development mode (-X dev) */
-    if (!_PyInterpreterState_GetConfig(interp)->dev_mode) {
+    if (!_PyInterpreterState_GetGlobalConfig(interp)->dev_mode) {
         return 0;
     }
 #else
@@ -1066,7 +1066,7 @@ _io_TextIOWrapper___init___impl(textio *self, PyObject *buffer,
 
     if (encoding == NULL) {
         PyInterpreterState *interp = _PyInterpreterState_GET();
-        if (_PyInterpreterState_GetConfig(interp)->warn_default_encoding) {
+        if (_PyInterpreterState_GetGlobalConfig(interp)->warn_default_encoding) {
             if (PyErr_WarnEx(PyExc_EncodingWarning,
                              "'encoding' argument not specified", 1)) {
                 return -1;
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 44e60d7c14954d..769ad9edb001e2 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -842,8 +842,8 @@ subprocess_fork_exec(PyObject *module, PyObject *args)
     }
 
     PyInterpreterState *interp = PyInterpreterState_Get();
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
-    if (config->_isolated_interpreter) {
+    const _PyInterpreterConfig *config = _PyInterpreterState_GetConfig(interp);
+    if (!config->allow_subprocess) {
         PyErr_SetString(PyExc_RuntimeError,
                         "subprocess not supported for isolated subinterpreters");
         return NULL;
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 02a061b84f85a3..a2cc0c7131b157 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -21,7 +21,7 @@
 #include "pycore_hashtable.h"    // _Py_hashtable_new()
 #include "pycore_initconfig.h"   // _Py_GetConfigsAsDict()
 #include "pycore_pathconfig.h"   // _PyPathConfig_ClearGlobal()
-#include "pycore_interp.h"       // _PyInterpreterState_GetConfigCopy()
+#include "pycore_interp.h"       // _Py_CopyConfig()
 #include "pycore_pyerrors.h"     // _Py_UTF8_Edit_Cost()
 #include "pycore_pystate.h"      // _PyThreadState_GET()
 #include "osdefs.h"              // MAXPATHLEN
@@ -252,7 +252,7 @@ test_get_config(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(args))
 {
     PyConfig config;
     PyConfig_InitIsolatedConfig(&config);
-    if (_PyInterpreterState_GetConfigCopy(&config) < 0) {
+    if (_Py_CopyConfig(&config) < 0) {
         PyConfig_Clear(&config);
         return NULL;
     }
@@ -270,7 +270,7 @@ test_set_config(PyObject *Py_UNUSED(self), PyObject *dict)
     if (_PyConfig_FromDict(&config, dict) < 0) {
         goto error;
     }
-    if (_PyInterpreterState_SetConfig(&config) < 0) {
+    if (_Py_SetConfig(&config) < 0) {
         goto error;
     }
     PyConfig_Clear(&config);
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index 4ac90dc8068934..eafdf0d0c49788 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -1128,7 +1128,7 @@ thread_PyThread_start_new_thread(PyObject *self, PyObject *fargs)
     }
 
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    if (interp->config._isolated_interpreter) {
+    if (!_PyInterpreterState_GetConfig(interp)->allow_threading) {
         PyErr_SetString(PyExc_RuntimeError,
                         "thread is not supported for isolated subinterpreters");
         return NULL;
diff --git a/Modules/_winapi.c b/Modules/_winapi.c
index 4845b4e6d4ad7c..443d2074a26572 100644
--- a/Modules/_winapi.c
+++ b/Modules/_winapi.c
@@ -1090,8 +1090,8 @@ _winapi_CreateProcess_impl(PyObject *module,
     }
 
     PyInterpreterState *interp = PyInterpreterState_Get();
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
-    if (config->_isolated_interpreter) {
+    const _PyInterpreterConfig *config = _PyInterpreterState_GetConfig(interp);
+    if (!config->allow_subprocess) {
         PyErr_SetString(PyExc_RuntimeError,
                         "subprocess not supported for isolated subinterpreters");
         return NULL;
diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index f40601ad3a1a72..82a5704fb1372f 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -2001,10 +2001,13 @@ interp_create(PyObject *self, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
+    // The struct is isolated by default.
+    const _PyInterpreterConfig config = (const _PyInterpreterConfig){};
+
     // Create and initialize the new interpreter.
     PyThreadState *save_tstate = _PyThreadState_GET();
     // XXX Possible GILState issues?
-    PyThreadState *tstate = _Py_NewInterpreter(isolated);
+    PyThreadState *tstate = _Py_NewInterpreter(isolated ? &config : NULL);
     PyThreadState_Swap(save_tstate);
     if (tstate == NULL) {
         /* Since no new thread state was created, there is no exception to
diff --git a/Modules/main.c b/Modules/main.c
index aa523fc58d93fb..3b8ae68c704a01 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -552,7 +552,7 @@ pymain_run_python(int *exitcode)
     PyObject *main_importer_path = NULL;
     PyInterpreterState *interp = _PyInterpreterState_GET();
     /* pymain_run_stdin() modify the config */
-    PyConfig *config = (PyConfig*)_PyInterpreterState_GetConfig(interp);
+    PyConfig *config = (PyConfig*)_PyInterpreterState_GetGlobalConfig(interp);
 
     /* ensure path config is written into global variables */
     if (_PyStatus_EXCEPTION(_PyPathConfig_UpdateGlobal(config))) {
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 3810bc87c1fbab..1ada15ee80474f 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -6777,7 +6777,7 @@ os_fork_impl(PyObject *module)
 {
     pid_t pid;
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    if (interp->config._isolated_interpreter) {
+    if (!_PyInterpreterState_GetConfig(interp)->allow_fork) {
         PyErr_SetString(PyExc_RuntimeError,
                         "fork not supported for isolated subinterpreters");
         return NULL;
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index bd169ed714212d..bc0570326a8f8b 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -436,7 +436,7 @@ unicode_check_encoding_errors(const char *encoding, const char *errors)
     PyInterpreterState *interp = _PyInterpreterState_GET();
 #ifndef Py_DEBUG
     /* In release mode, only check in development mode (-X dev) */
-    if (!_PyInterpreterState_GetConfig(interp)->dev_mode) {
+    if (!_PyInterpreterState_GetGlobalConfig(interp)->dev_mode) {
         return 0;
     }
 #else
@@ -3324,7 +3324,7 @@ PyUnicode_EncodeFSDefault(PyObject *unicode)
         /* Before _PyUnicode_InitEncodings() is called, the Python codec
            machinery is not ready and so cannot be used:
            use wcstombs() in this case. */
-        const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+        const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
         const wchar_t *filesystem_errors = config->filesystem_errors;
         assert(filesystem_errors != NULL);
         _Py_error_handler errors = get_error_handler_wide(filesystem_errors);
@@ -3562,7 +3562,7 @@ PyUnicode_DecodeFSDefaultAndSize(const char *s, Py_ssize_t size)
         /* Before _PyUnicode_InitEncodings() is called, the Python codec
            machinery is not ready and so cannot be used:
            use mbstowcs() in this case. */
-        const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+        const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
         const wchar_t *filesystem_errors = config->filesystem_errors;
         assert(filesystem_errors != NULL);
         _Py_error_handler errors = get_error_handler_wide(filesystem_errors);
@@ -15026,7 +15026,7 @@ static PyStatus
 init_stdio_encoding(PyInterpreterState *interp)
 {
     /* Update the stdio encoding to the normalized Python codec name. */
-    PyConfig *config = (PyConfig*)_PyInterpreterState_GetConfig(interp);
+    PyConfig *config = (PyConfig*)_PyInterpreterState_GetGlobalConfig(interp);
     if (config_get_codec_name(&config->stdio_encoding) < 0) {
         return _PyStatus_ERR("failed to get the Python codec name "
                              "of the stdio encoding");
@@ -15038,7 +15038,7 @@ init_stdio_encoding(PyInterpreterState *interp)
 static int
 init_fs_codec(PyInterpreterState *interp)
 {
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
 
     _Py_error_handler error_handler;
     error_handler = get_error_handler_wide(config->filesystem_errors);
@@ -15097,7 +15097,7 @@ init_fs_encoding(PyThreadState *tstate)
     /* Update the filesystem encoding to the normalized Python codec name.
        For example, replace "ANSI_X3.4-1968" (locale encoding) with "ascii"
        (Python codec name). */
-    PyConfig *config = (PyConfig*)_PyInterpreterState_GetConfig(interp);
+    PyConfig *config = (PyConfig*)_PyInterpreterState_GetGlobalConfig(interp);
     if (config_get_codec_name(&config->filesystem_encoding) < 0) {
         _Py_DumpPathConfig(tstate);
         return _PyStatus_ERR("failed to get the Python codec "
@@ -15140,7 +15140,7 @@ int
 _PyUnicode_EnableLegacyWindowsFSEncoding(void)
 {
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    PyConfig *config = (PyConfig *)_PyInterpreterState_GetConfig(interp);
+    PyConfig *config = (PyConfig *)_PyInterpreterState_GetGlobalConfig(interp);
 
     /* Set the filesystem encoding to mbcs/replace (PEP 529) */
     wchar_t *encoding = _PyMem_RawWcsdup(L"mbcs");
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index f84445690eb8f6..33c936ac51f93b 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -681,8 +681,6 @@ static int test_init_from_config(void)
 
     config.safe_path = 1;
 
-    config._isolated_interpreter = 1;
-
     init_from_config_clear(&config);
 
     dump_config();
@@ -1651,7 +1649,7 @@ static int tune_config(void)
 {
     PyConfig config;
     PyConfig_InitPythonConfig(&config);
-    if (_PyInterpreterState_GetConfigCopy(&config) < 0) {
+    if (_Py_CopyConfig(&config) < 0) {
         PyConfig_Clear(&config);
         PyErr_Print();
         return -1;
@@ -1659,7 +1657,7 @@ static int tune_config(void)
 
     config.bytes_warning = 2;
 
-    if (_PyInterpreterState_SetConfig(&config) < 0) {
+    if (_Py_SetConfig(&config) < 0) {
         PyConfig_Clear(&config);
         return -1;
     }
@@ -1678,7 +1676,7 @@ static int test_init_set_config(void)
     config.bytes_warning = 0;
     init_from_config_clear(&config);
 
-    // Tune the configuration using _PyInterpreterState_SetConfig()
+    // Tune the configuration using _Py_SetConfig()
     if (tune_config() < 0) {
         PyErr_Print();
         return 1;
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 6284bbdf97468e..8ae9e3de48e17e 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -3020,7 +3020,7 @@ _PyBuiltin_Init(PyInterpreterState *interp)
 {
     PyObject *mod, *dict, *debug;
 
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
 
     mod = _PyModule_CreateInitialized(&builtinsmodule, PYTHON_API_VERSION);
     if (mod == NULL)
diff --git a/Python/dynload_win.c b/Python/dynload_win.c
index c03bc5602bffee..c11045395bd2e0 100644
--- a/Python/dynload_win.c
+++ b/Python/dynload_win.c
@@ -204,7 +204,7 @@ _Py_CheckPython3(void)
     /* For back-compat, also search {sys.prefix}\DLLs, though
        that has not been a normal install layout for a while */
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    PyConfig *config = (PyConfig*)_PyInterpreterState_GetConfig(interp);
+    PyConfig *config = (PyConfig*)_PyInterpreterState_GetGlobalConfig(interp);
     assert(config->prefix);
     if (config->prefix) {
         wcscpy_s(py3path, MAXPATHLEN, config->prefix);
diff --git a/Python/import.c b/Python/import.c
index 54c21fa4a56aa9..356127e52a289c 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -58,7 +58,7 @@ _PyImportZip_Init(PyThreadState *tstate)
         goto error;
     }
 
-    int verbose = _PyInterpreterState_GetConfig(tstate->interp)->verbose;
+    int verbose = _PyInterpreterState_GetGlobalConfig(tstate->interp)->verbose;
     if (verbose) {
         PySys_WriteStderr("# installing zipimport hook\n");
     }
@@ -531,7 +531,7 @@ import_find_extension(PyThreadState *tstate, PyObject *name,
         return NULL;
     }
 
-    int verbose = _PyInterpreterState_GetConfig(tstate->interp)->verbose;
+    int verbose = _PyInterpreterState_GetGlobalConfig(tstate->interp)->verbose;
     if (verbose) {
         PySys_FormatStderr("import %U # previously loaded (%R)\n",
                            name, filename);
@@ -1064,7 +1064,7 @@ use_frozen(void)
         return false;
     }
     else {
-        return interp->config.use_frozen_modules;
+        return _PyInterpreterState_GetGlobalConfig(interp)->use_frozen_modules;
     }
 }
 
@@ -1479,7 +1479,7 @@ remove_importlib_frames(PyThreadState *tstate)
        which end with a call to "_call_with_frames_removed". */
 
     _PyErr_Fetch(tstate, &exception, &value, &base_tb);
-    if (!exception || _PyInterpreterState_GetConfig(tstate->interp)->verbose) {
+    if (!exception || _PyInterpreterState_GetGlobalConfig(tstate->interp)->verbose) {
         goto done;
     }
 
@@ -1684,7 +1684,7 @@ import_find_and_load(PyThreadState *tstate, PyObject *abs_name)
 {
     PyObject *mod = NULL;
     PyInterpreterState *interp = tstate->interp;
-    int import_time = _PyInterpreterState_GetConfig(interp)->import_time;
+    int import_time = _PyInterpreterState_GetGlobalConfig(interp)->import_time;
     static int import_level;
     static _PyTime_t accumulated;
 
diff --git a/Python/initconfig.c b/Python/initconfig.c
index f18ec4068bc443..b69e9b12be33bc 100644
--- a/Python/initconfig.c
+++ b/Python/initconfig.c
@@ -779,7 +779,6 @@ _PyConfig_InitCompatConfig(PyConfig *config)
     config->check_hash_pycs_mode = NULL;
     config->pathconfig_warnings = -1;
     config->_init_main = 1;
-    config->_isolated_interpreter = 0;
 #ifdef MS_WINDOWS
     config->legacy_windows_stdio = -1;
 #endif
@@ -1016,7 +1015,6 @@ _PyConfig_Copy(PyConfig *config, const PyConfig *config2)
     COPY_WSTR_ATTR(check_hash_pycs_mode);
     COPY_ATTR(pathconfig_warnings);
     COPY_ATTR(_init_main);
-    COPY_ATTR(_isolated_interpreter);
     COPY_ATTR(use_frozen_modules);
     COPY_ATTR(safe_path);
     COPY_WSTRLIST(orig_argv);
@@ -1123,7 +1121,6 @@ _PyConfig_AsDict(const PyConfig *config)
     SET_ITEM_WSTR(check_hash_pycs_mode);
     SET_ITEM_INT(pathconfig_warnings);
     SET_ITEM_INT(_init_main);
-    SET_ITEM_INT(_isolated_interpreter);
     SET_ITEM_WSTRLIST(orig_argv);
     SET_ITEM_INT(use_frozen_modules);
     SET_ITEM_INT(safe_path);
@@ -1411,7 +1408,6 @@ _PyConfig_FromDict(PyConfig *config, PyObject *dict)
 
     GET_UINT(_install_importlib);
     GET_UINT(_init_main);
-    GET_UINT(_isolated_interpreter);
     GET_UINT(use_frozen_modules);
     GET_UINT(safe_path);
     GET_UINT(_is_python_build);
@@ -3066,7 +3062,7 @@ _Py_GetConfigsAsDict(void)
     Py_CLEAR(dict);
 
     /* core config */
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
     dict = _PyConfig_AsDict(config);
     if (dict == NULL) {
         goto error;
@@ -3133,7 +3129,7 @@ _Py_DumpPathConfig(PyThreadState *tstate)
             PySys_WriteStderr("\n"); \
         } while (0)
 
-    const PyConfig *config = _PyInterpreterState_GetConfig(tstate->interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(tstate->interp);
     DUMP_CONFIG("PYTHONHOME", home);
     DUMP_CONFIG("PYTHONPATH", pythonpath_env);
     DUMP_CONFIG("program name", program_name);
@@ -3182,3 +3178,22 @@ _Py_DumpPathConfig(PyThreadState *tstate)
 
     _PyErr_Restore(tstate, exc_type, exc_value, exc_tb);
 }
+
+
+/* --- _PyInterpreterConfig ---------------------------------- */
+
+void
+_PyInterpreterConfig_Clear(_PyInterpreterConfig *config)
+{
+    *config = (_PyInterpreterConfig){};
+}
+
+
+PyStatus
+_PyInterpreterConfig_Copy(_PyInterpreterConfig *config,
+                          const _PyInterpreterConfig *config2)
+{
+    *config = *config2;
+
+    return _PyStatus_OK();
+}
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index c550f13bc14820..404b1a78e4d556 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -177,7 +177,7 @@ init_importlib(PyThreadState *tstate, PyObject *sysmod)
     assert(!_PyErr_Occurred(tstate));
 
     PyInterpreterState *interp = tstate->interp;
-    int verbose = _PyInterpreterState_GetConfig(interp)->verbose;
+    int verbose = _PyInterpreterState_GetGlobalConfig(interp)->verbose;
 
     // Import _importlib through its frozen version, _frozen_importlib.
     if (verbose) {
@@ -460,26 +460,28 @@ _Py_SetLocaleFromEnv(int category)
 
 
 static int
-interpreter_update_config(PyThreadState *tstate, int only_update_path_config)
+runtime_update_config(_PyRuntimeState *runtime, int only_update_path_config)
 {
-    const PyConfig *config = &tstate->interp->config;
-
     if (!only_update_path_config) {
-        PyStatus status = _PyConfig_Write(config, tstate->interp->runtime);
+        PyStatus status = _PyConfig_Write(&runtime->config, runtime);
         if (_PyStatus_EXCEPTION(status)) {
             _PyErr_SetFromPyStatus(status);
             return -1;
         }
     }
 
-    if (_Py_IsMainInterpreter(tstate->interp)) {
-        PyStatus status = _PyPathConfig_UpdateGlobal(config);
-        if (_PyStatus_EXCEPTION(status)) {
-            _PyErr_SetFromPyStatus(status);
-            return -1;
-        }
+    PyStatus status = _PyPathConfig_UpdateGlobal(&runtime->config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyErr_SetFromPyStatus(status);
+        return -1;
     }
 
+    return 0;
+}
+
+static int
+interpreter_update_config(PyThreadState *tstate)
+{
     // Update the sys module for the new configuration
     if (_PySys_UpdateConfig(tstate) < 0) {
         return -1;
@@ -489,7 +491,7 @@ interpreter_update_config(PyThreadState *tstate, int only_update_path_config)
 
 
 int
-_PyInterpreterState_SetConfig(const PyConfig *src_config)
+_Py_SetConfig(const PyConfig *src_config)
 {
     PyThreadState *tstate = _PyThreadState_GET();
     int res = -1;
@@ -508,13 +510,20 @@ _PyInterpreterState_SetConfig(const PyConfig *src_config)
         goto done;
     }
 
-    status = _PyConfig_Copy(&tstate->interp->config, &config);
+    status = _PyConfig_Copy(&tstate->interp->runtime->config, &config);
     if (_PyStatus_EXCEPTION(status)) {
         _PyErr_SetFromPyStatus(status);
         goto done;
     }
 
-    res = interpreter_update_config(tstate, 0);
+    if (_Py_IsMainInterpreter(tstate->interp)) {
+        res = runtime_update_config(tstate->interp->runtime, 0);
+        if (res < 0) {
+            goto done;
+        }
+    }
+
+    res = interpreter_update_config(tstate);
 
 done:
     PyConfig_Clear(&config);
@@ -550,17 +559,19 @@ pyinit_core_reconfigure(_PyRuntimeState *runtime,
     if (interp == NULL) {
         return _PyStatus_ERR("can't make main interpreter");
     }
+    assert(interp->runtime == runtime);
+    assert(_Py_IsMainInterpreter(interp));
 
     status = _PyConfig_Write(config, runtime);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
 
-    status = _PyConfig_Copy(&interp->config, config);
+    status = _PyConfig_Copy(&runtime->config, config);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
-    config = _PyInterpreterState_GetConfig(interp);
+    config = _PyInterpreterState_GetGlobalConfig(interp);
 
     if (config->_install_importlib) {
         status = _PyPathConfig_UpdateGlobal(config);
@@ -649,9 +660,10 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
     if (interp == NULL) {
         return _PyStatus_ERR("can't make main interpreter");
     }
+    assert(interp->runtime == runtime);
     assert(_Py_IsMainInterpreter(interp));
 
-    status = _PyConfig_Copy(&interp->config, config);
+    status = _PyConfig_Copy(&runtime->config, config);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
@@ -863,7 +875,7 @@ pycore_interp_init(PyThreadState *tstate)
         goto done;
     }
 
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
     if (config->_install_importlib) {
         /* This call sets up builtin and frozen import support */
         if (init_importlib(tstate, sysmod) < 0) {
@@ -1079,7 +1091,12 @@ pyinit_core(_PyRuntimeState *runtime,
 static PyStatus
 pyinit_main_reconfigure(PyThreadState *tstate)
 {
-    if (interpreter_update_config(tstate, 0) < 0) {
+    if (_Py_IsMainInterpreter(tstate->interp)) {
+        if (runtime_update_config(tstate->interp->runtime, 0) < 0) {
+            return _PyStatus_ERR("fail to reconfigure Python");
+        }
+    }
+    if (interpreter_update_config(tstate) < 0) {
         return _PyStatus_ERR("fail to reconfigure Python");
     }
     return _PyStatus_OK();
@@ -1094,7 +1111,7 @@ init_interp_main(PyThreadState *tstate)
     PyStatus status;
     int is_main_interp = _Py_IsMainInterpreter(tstate->interp);
     PyInterpreterState *interp = tstate->interp;
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
 
     if (!config->_install_importlib) {
         /* Special mode for freeze_importlib: run with no import system
@@ -1108,13 +1125,18 @@ init_interp_main(PyThreadState *tstate)
         return _PyStatus_OK();
     }
 
-    // Initialize the import-related configuration.
-    status = _PyConfig_InitImportConfig(&interp->config);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
+    if (is_main_interp) {
+        // Initialize the import-related configuration.
+        status = _PyConfig_InitImportConfig(&interp->runtime->config);
+        if (_PyStatus_EXCEPTION(status)) {
+            return status;
+        }
 
-    if (interpreter_update_config(tstate, 1) < 0) {
+        if (runtime_update_config(tstate->interp->runtime, 1) < 0) {
+            return _PyStatus_ERR("failed to update the Python config");
+        }
+    }
+    if (interpreter_update_config(tstate) < 0) {
         return _PyStatus_ERR("failed to update the Python config");
     }
 
@@ -1257,7 +1279,7 @@ Py_InitializeFromConfig(const PyConfig *config)
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
-    config = _PyInterpreterState_GetConfig(tstate->interp);
+    config = _PyInterpreterState_GetGlobalConfig(tstate->interp);
 
     if (config->_init_main) {
         status = pyinit_main(tstate);
@@ -1530,7 +1552,7 @@ finalize_modules(PyThreadState *tstate)
         // Already done
         return;
     }
-    int verbose = _PyInterpreterState_GetConfig(interp)->verbose;
+    int verbose = _PyInterpreterState_GetGlobalConfig(interp)->verbose;
 
     // Delete some special builtins._ and sys attributes first.  These are
     // common places where user values hide and people complain when their
@@ -1787,14 +1809,14 @@ Py_FinalizeEx(void)
     /* Copy the core config, PyInterpreterState_Delete() free
        the core config memory */
 #ifdef Py_REF_DEBUG
-    int show_ref_count = tstate->interp->config.show_ref_count;
+    int show_ref_count = runtime->config.show_ref_count;
 #endif
 #ifdef Py_TRACE_REFS
-    int dump_refs = tstate->interp->config.dump_refs;
-    wchar_t *dump_refs_file = tstate->interp->config.dump_refs_file;
+    int dump_refs = runtime->config.dump_refs;
+    wchar_t *dump_refs_file = runtime->config.dump_refs_file;
 #endif
 #ifdef WITH_PYMALLOC
-    int malloc_stats = tstate->interp->config.malloc_stats;
+    int malloc_stats = runtime->config.malloc_stats;
 #endif
 
     /* Remaining daemon threads will automatically exit
@@ -1959,7 +1981,7 @@ Py_Finalize(void)
 */
 
 static PyStatus
-new_interpreter(PyThreadState **tstate_p, int isolated_subinterpreter)
+new_interpreter(PyThreadState **tstate_p, const _PyInterpreterConfig *config)
 {
     PyStatus status;
 
@@ -1993,23 +2015,15 @@ new_interpreter(PyThreadState **tstate_p, int isolated_subinterpreter)
     PyThreadState *save_tstate = PyThreadState_Swap(tstate);
 
     /* Copy the current interpreter config into the new interpreter */
-    const PyConfig *config;
-    if (save_tstate != NULL) {
-        config = _PyInterpreterState_GetConfig(save_tstate->interp);
-    }
-    else
-    {
+    if (config == NULL) {
         /* No current thread state, copy from the main interpreter */
         PyInterpreterState *main_interp = _PyInterpreterState_Main();
         config = _PyInterpreterState_GetConfig(main_interp);
     }
-
-
-    status = _PyConfig_Copy(&interp->config, config);
+    status = _PyInterpreterConfig_Copy(&interp->config, config);
     if (_PyStatus_EXCEPTION(status)) {
         goto error;
     }
-    interp->config._isolated_interpreter = isolated_subinterpreter;
 
     status = init_interp_create_gil(tstate);
     if (_PyStatus_EXCEPTION(status)) {
@@ -2043,10 +2057,10 @@ new_interpreter(PyThreadState **tstate_p, int isolated_subinterpreter)
 }
 
 PyThreadState *
-_Py_NewInterpreter(int isolated_subinterpreter)
+_Py_NewInterpreter(const _PyInterpreterConfig *config)
 {
     PyThreadState *tstate = NULL;
-    PyStatus status = new_interpreter(&tstate, isolated_subinterpreter);
+    PyStatus status = new_interpreter(&tstate, config);
     if (_PyStatus_EXCEPTION(status)) {
         Py_ExitStatusException(status);
     }
@@ -2057,7 +2071,7 @@ _Py_NewInterpreter(int isolated_subinterpreter)
 PyThreadState *
 Py_NewInterpreter(void)
 {
-    return _Py_NewInterpreter(0);
+    return _Py_NewInterpreter(NULL);
 }
 
 /* Delete an interpreter and its last thread.  This requires that the
@@ -2393,7 +2407,7 @@ init_sys_streams(PyThreadState *tstate)
     int fd;
     PyObject * encoding_attr;
     PyStatus res = _PyStatus_OK();
-    const PyConfig *config = _PyInterpreterState_GetConfig(tstate->interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(tstate->interp);
 
     /* Check that stdin is not a directory
        Using shell redirection, you can redirect stdin to a directory,
diff --git a/Python/pystate.c b/Python/pystate.c
index a0d61d7ebb3be9..1ef3819b7d06d1 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -134,6 +134,8 @@ init_runtime(_PyRuntimeState *runtime,
     // Set it to the ID of the main thread of the main interpreter.
     runtime->main_thread = PyThread_get_thread_ident();
 
+    PyConfig_InitPythonConfig(&runtime->config);
+
     runtime->unicode_ids.next_index = unicode_next_index;
     runtime->unicode_ids.lock = unicode_ids_mutex;
 
@@ -188,6 +190,8 @@ _PyRuntimeState_Fini(_PyRuntimeState *runtime)
 
 #undef FREE_LOCK
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
+
+    PyConfig_Clear(&runtime->config);
 }
 
 #ifdef HAVE_FORK
@@ -307,7 +311,6 @@ init_interpreter(PyInterpreterState *interp,
 
     _PyEval_InitState(&interp->ceval, pending_lock);
     _PyGC_InitState(&interp->gc);
-    PyConfig_InitPythonConfig(&interp->config);
     _PyType_InitCache(interp);
 
     interp->_initialized = 1;
@@ -415,7 +418,6 @@ interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
 
     Py_CLEAR(interp->audit_hooks);
 
-    PyConfig_Clear(&interp->config);
     Py_CLEAR(interp->codec_search_path);
     Py_CLEAR(interp->codec_search_cache);
     Py_CLEAR(interp->codec_error_registry);
@@ -1017,7 +1019,7 @@ _PyInterpreterState_ClearModules(PyInterpreterState *interp)
 void
 PyThreadState_Clear(PyThreadState *tstate)
 {
-    int verbose = _PyInterpreterState_GetConfig(tstate->interp)->verbose;
+    int verbose = _PyInterpreterState_GetGlobalConfig(tstate->interp)->verbose;
 
     if (verbose && tstate->cframe->current_frame != NULL) {
         /* bpo-20526: After the main thread calls
@@ -2139,19 +2141,26 @@ _PyInterpreterState_SetEvalFrameFunc(PyInterpreterState *interp,
 }
 
 
-const PyConfig*
+const _PyInterpreterConfig*
 _PyInterpreterState_GetConfig(PyInterpreterState *interp)
 {
     return &interp->config;
 }
 
 
+const PyConfig*
+_PyInterpreterState_GetGlobalConfig(PyInterpreterState *interp)
+{
+    return &interp->runtime->config;
+}
+
+
 int
-_PyInterpreterState_GetConfigCopy(PyConfig *config)
+_Py_CopyConfig(PyConfig *config)
 {
     PyInterpreterState *interp = PyInterpreterState_Get();
 
-    PyStatus status = _PyConfig_Copy(config, &interp->config);
+    PyStatus status = _PyConfig_Copy(config, &interp->runtime->config);
     if (PyStatus_Exception(status)) {
         _PyErr_SetFromPyStatus(status);
         return -1;
@@ -2166,7 +2175,7 @@ _Py_GetConfig(void)
     assert(PyGILState_Check());
     PyThreadState *tstate = _PyThreadState_GET();
     _Py_EnsureTstateNotNULL(tstate);
-    return _PyInterpreterState_GetConfig(tstate->interp);
+    return _PyInterpreterState_GetGlobalConfig(tstate->interp);
 }
 
 #define MINIMUM_OVERHEAD 1000
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 653b5a55e885e5..209eddb2fbbfe1 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -330,7 +330,7 @@ _PySys_ClearAuditHooks(PyThreadState *ts)
         return;
     }
 
-    const PyConfig *config = _PyInterpreterState_GetConfig(ts->interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(ts->interp);
     if (config->verbose) {
         PySys_WriteStderr("# clear sys.audit hooks\n");
     }
@@ -854,7 +854,7 @@ sys_getfilesystemencoding_impl(PyObject *module)
 /*[clinic end generated code: output=1dc4bdbe9be44aa7 input=8475f8649b8c7d8c]*/
 {
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
     return PyUnicode_FromWideChar(config->filesystem_encoding, -1);
 }
 
@@ -869,7 +869,7 @@ sys_getfilesystemencodeerrors_impl(PyObject *module)
 /*[clinic end generated code: output=ba77b36bbf7c96f5 input=22a1e8365566f1e5]*/
 {
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
     return PyUnicode_FromWideChar(config->filesystem_errors, -1);
 }
 
@@ -2776,7 +2776,7 @@ static int
 set_flags_from_config(PyInterpreterState *interp, PyObject *flags)
 {
     const PyPreConfig *preconfig = &interp->runtime->preconfig;
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
 
     // _PySys_UpdateConfig() modifies sys.flags in-place:
     // Py_XDECREF() is needed in this case.
@@ -3298,7 +3298,7 @@ _PySys_UpdateConfig(PyThreadState *tstate)
 {
     PyInterpreterState *interp = tstate->interp;
     PyObject *sysdict = interp->sysdict;
-    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+    const PyConfig *config = _PyInterpreterState_GetGlobalConfig(interp);
     int res;
 
 #define COPY_LIST(KEY, VALUE) \