diff --git a/awscli/customizations/s3/factory.py b/awscli/customizations/s3/factory.py
index 2ad7127e1ee1..b866f7ec7894 100644
--- a/awscli/customizations/s3/factory.py
+++ b/awscli/customizations/s3/factory.py
@@ -27,6 +27,7 @@
 from awscli.compat import urlparse
 from awscli.customizations.s3 import constants
 from awscli.customizations.s3.transferconfig import (
+    DEFAULTS,
     create_transfer_config_from_runtime_config,
 )
 
@@ -157,16 +158,27 @@ def _create_crt_client(self, params, runtime_config):
         return create_s3_crt_client(**create_crt_client_kwargs)
 
     def _resolve_crt_client_config_kwargs(self, runtime_config):
+        use_defaults = self._should_use_transfer_config_defaults(
+            runtime_config
+        )
         kwargs = {}
         for config_name, crt_name in CRT_CLIENT_KWARG_MAP.items():
             if runtime_config.is_explicitly_set(config_name):
                 kwargs[crt_name] = runtime_config[config_name]
+            elif use_defaults:
+                kwargs[crt_name] = DEFAULTS[config_name]
         if 'part_size' not in kwargs:
             # `create_s3_crt_client` defaults this to 8MB, so `None` has to be
             # passed to opt into the CRT's dynamic part size calculation.
             kwargs['part_size'] = None
         return kwargs
 
+    def _should_use_transfer_config_defaults(self, runtime_config):
+        preferred = runtime_config.get('preferred_transfer_client')
+        if preferred == constants.CRT_TRANSFER_CLIENT:
+            return False
+        return not awscrt.s3.is_optimized_for_system()
+
     def _create_crt_request_serializer(self, params):
         return BotocoreCRTRequestSerializer(
             self._session,
diff --git a/tests/unit/customizations/s3/test_factory.py b/tests/unit/customizations/s3/test_factory.py
index 8592714d2a8c..69c7a2c10118 100644
--- a/tests/unit/customizations/s3/test_factory.py
+++ b/tests/unit/customizations/s3/test_factory.py
@@ -21,6 +21,7 @@
 from s3transfer.crt import CRTTransferManager
 from s3transfer.manager import TransferManager
 
+from awscli.customizations.s3 import constants
 from awscli.customizations.s3.factory import (
     ClientFactory,
     TransferManagerFactory,
@@ -603,6 +604,70 @@ def test_max_concurrent_requests_configure_for_crt_manager(
             mock_crt_client.call_args[1]['max_active_connections_override'], 3
         )
 
+    def test_optimized_system_does_not_use_transfer_config_defaults(self):
+        runtime_config = self.get_runtime_config()
+        with mock.patch(
+            'awscrt.s3.is_optimized_for_system', return_value=True
+        ):
+            self.assertFalse(
+                self.factory._should_use_transfer_config_defaults(
+                    runtime_config
+                )
+            )
+
+    def test_explicit_crt_does_not_use_transfer_config_defaults(self):
+        runtime_config = self.get_runtime_config(
+            preferred_transfer_client='crt'
+        )
+        with mock.patch(
+            'awscrt.s3.is_optimized_for_system', return_value=False
+        ):
+            self.assertFalse(
+                self.factory._should_use_transfer_config_defaults(
+                    runtime_config
+                )
+            )
+
+    def test_newly_eligible_system_uses_transfer_config_defaults(self):
+        runtime_config = self.get_runtime_config()
+        with mock.patch(
+            'awscrt.s3.is_optimized_for_system', return_value=False
+        ):
+            self.assertTrue(
+                self.factory._should_use_transfer_config_defaults(
+                    runtime_config
+                )
+            )
+
+    @mock.patch('awscrt.s3.is_optimized_for_system', return_value=False)
+    @mock.patch('s3transfer.crt.S3Client')
+    def test_transfer_config_defaults_passed_for_newly_eligible_system(
+        self, mock_crt_client, mock_is_optimized
+    ):
+        self.runtime_config = self.get_runtime_config()
+        with mock.patch.object(
+            self.factory,
+            '_resolve_transfer_client_type_for_system',
+            return_value=constants.CRT_TRANSFER_CLIENT,
+        ):
+            transfer_manager = self.factory.create_transfer_manager(
+                self.params, self.runtime_config
+            )
+        self.assert_is_crt_manager(transfer_manager)
+        call_kwargs = mock_crt_client.call_args[1]
+        defaults = RuntimeConfig.defaults()
+        self.assertEqual(
+            call_kwargs['part_size'], defaults['multipart_chunksize']
+        )
+        self.assertEqual(
+            call_kwargs['multipart_upload_threshold'],
+            defaults['multipart_threshold'],
+        )
+        self.assertEqual(
+            call_kwargs['max_active_connections_override'],
+            defaults['max_concurrent_requests'],
+        )
+
     @mock.patch('s3transfer.crt.S3Client')
     def test_unconfigured_options_not_passed_to_crt_manager(
         self, mock_crt_client