diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
@@ -412,13 +412,13 @@ Miscellaneous options
     application.  Typical usage is ``python3 -X importtime -c 'import
     asyncio'``.  See also :envvar:`PYTHONPROFILEIMPORTTIME`.
   * ``-X dev`` enables the "developer mode": enable debug checks at runtime.
-     In short, ``python3 -X dev ...`` behaves as ``PYTHONMALLOC=debug PYTHONASYNCIODEBUG=1 python3
-     -W default -X faulthandler ...``, except that the :envvar:`PYTHONMALLOC`
-     and :envvar:`PYTHONASYNCIODEBUG` environment variables are not set in
-     practice. Developer mode:

-     * Add ``default`` warnings option. For example, display
-       :exc:`DeprecationWarning` and :exc:`ResourceWarning` warnings.
     * Install debug hooks on memory allocators: see the
       :c:func:`PyMem_SetupDebugHooks` C function.
     * Enable the :mod:`faulthandler` module to dump the Python traceback

diff --git a/Include/pystate.h b/Include/pystate.h
@@ -33,6 +33,7 @@ typedef struct {
    int faulthandler;
    int tracemalloc;        /* Number of saved frames, 0=don't trace */
    int importtime;         /* -X importtime */
} _PyCoreConfig;

#define _PyCoreConfig_INIT \
@@ -43,7 +44,8 @@ typedef struct {
     .allocator = NULL, \
     .faulthandler = 0, \
     .tracemalloc = 0, \
-     .importtime = 0}

/* Placeholders while working on the new configuration API
 *

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
@@ -262,15 +262,11 @@ def _args_from_interpreter_flags():
            args.append('-' + opt * v)

    # -W options
-    warnoptions = sys.warnoptions
-    xoptions = getattr(sys, '_xoptions', {})
-    if 'dev' in xoptions and warnoptions and warnoptions[-1] == 'default':
-        # special case: -X dev adds 'default' to sys.warnoptions
-        warnoptions = warnoptions[:-1]
-    for opt in warnoptions:
        args.append('-W' + opt)

    # -X options
    if 'dev' in xoptions:
        args.extend(('-X', 'dev'))
    for opt in ('faulthandler', 'tracemalloc', 'importtime',

diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
@@ -507,14 +507,14 @@ def test_sys_flags_set(self):
            with self.subTest(envar_value=value):
                assert_python_ok('-c', code, **env_vars)

-    def run_xdev(self, code, check_exitcode=True):
        env = dict(os.environ)
        env.pop('PYTHONWARNINGS', None)
        # Force malloc() to disable the debug hooks which are enabled
        # by default for Python compiled in debug mode
        env['PYTHONMALLOC'] = 'malloc'

-        args = (sys.executable, '-X', 'dev', '-c', code)
        proc = subprocess.run(args,
                              stdout=subprocess.PIPE,
                              stderr=subprocess.STDOUT,
@@ -525,8 +525,34 @@ def run_xdev(self, code, check_exitcode=True):
        return proc.stdout.rstrip()

    def test_xdev(self):
-        out = self.run_xdev("import sys; print(sys.warnoptions)")
-        self.assertEqual(out, "['default']")

        try:
            import _testcapi
@@ -535,7 +561,7 @@ def test_xdev(self):
        else:
            code = "import _testcapi; _testcapi.pymem_api_misuse()"
            with support.SuppressCrashReport():
-                out = self.run_xdev(code, check_exitcode=False)
            self.assertIn("Debug memory block at address p=", out)

        try:
@@ -544,9 +570,23 @@ def test_xdev(self):
            pass
        else:
            code = "import faulthandler; print(faulthandler.is_enabled())"
-            out = self.run_xdev(code)
            self.assertEqual(out, "True")

class IgnoreEnvironmentTest(unittest.TestCase):

    def run_ignoring_vars(self, predicate, **env_vars):

diff --git a/Lib/warnings.py b/Lib/warnings.py
@@ -486,7 +486,6 @@ def __exit__(self, *exc_info):
# - a compiled regex that must match the module that is being warned
# - a line number for the line being warning, or 0 to mean any line
# If either if the compiled regexs are None, match anything.
-_warnings_defaults = False
try:
    from _warnings import (filters, _defaultaction, _onceregistry,
                           warn, warn_explicit, _filters_mutated)
@@ -504,12 +503,16 @@ def _filters_mutated():
        global _filters_version
        _filters_version += 1


# Module initialization
_processoptions(sys.warnoptions)
if not _warnings_defaults:
    py_debug = hasattr(sys, 'gettotalrefcount')
-    if not py_debug:
        silence = [ImportWarning, PendingDeprecationWarning]
        silence.append(DeprecationWarning)
        for cls in silence:
@@ -525,10 +528,15 @@ def _filters_mutated():
    simplefilter(bytes_action, category=BytesWarning, append=1)

    # resource usage warnings are enabled by default in pydebug mode
-    if py_debug:
        resource_action = "always"
    else:
        resource_action = "ignore"
    simplefilter(resource_action, category=ResourceWarning, append=1)

del _warnings_defaults
diff --git a/Modules/main.c b/Modules/main.c
@@ -1397,14 +1397,9 @@ pymain_parse_envvars(_PyMain *pymain)
        return -1;
    }
    if (pymain_get_xoption(pymain, L"dev")) {
-        /* "python3 -X dev ..." behaves
-           as "PYTHONMALLOC=debug python3 -Wd -X faulthandler ..." */
-        core_config->allocator = "debug";
-        if (pymain_optlist_append(pymain, &pymain->cmdline.warning_options,
-                                  L"default") < 0) {
-            return -1;
-        }
        core_config->faulthandler = 1;
    }
    return 0;
}

diff --git a/Python/_warnings.c b/Python/_warnings.c
@@ -1196,11 +1196,19 @@ create_filter(PyObject *category, const char *action)
static PyObject *
init_filters(void)
{
#ifndef Py_DEBUG
-    PyObject *filters = PyList_New(5);
-#else
-    PyObject *filters = PyList_New(2);
#endif
    unsigned int pos = 0;  /* Post-incremented in each use. */
    unsigned int x;
    const char *bytes_action, *resource_action;
@@ -1209,12 +1217,14 @@ init_filters(void)
        return NULL;

#ifndef Py_DEBUG
-    PyList_SET_ITEM(filters, pos++,
-                    create_filter(PyExc_DeprecationWarning, "ignore"));
-    PyList_SET_ITEM(filters, pos++,
-                    create_filter(PyExc_PendingDeprecationWarning, "ignore"));
-    PyList_SET_ITEM(filters, pos++,
-                    create_filter(PyExc_ImportWarning, "ignore"));
#endif

    if (Py_BytesWarningFlag > 1)
@@ -1225,14 +1235,21 @@ init_filters(void)
        bytes_action = "ignore";
    PyList_SET_ITEM(filters, pos++, create_filter(PyExc_BytesWarning,
                    bytes_action));
    /* resource usage warnings are enabled by default in pydebug mode */
#ifdef Py_DEBUG
    resource_action = "always";
#else
-    resource_action = "ignore";
#endif
    PyList_SET_ITEM(filters, pos++, create_filter(PyExc_ResourceWarning,
                    resource_action));
    for (x = 0; x < pos; x += 1) {
        if (PyList_GET_ITEM(filters, x) == NULL) {
            Py_DECREF(filters);