diff --git a/optimizely/entities.py b/optimizely/entities.py
index 6aa0060d..589ca984 100644
--- a/optimizely/entities.py
+++ b/optimizely/entities.py
@@ -22,7 +22,7 @@
 
 if TYPE_CHECKING:
     # prevent circular dependenacy by skipping import at runtime
-    from .helpers.types import ExperimentDict, ExperimentType, TrafficAllocation, VariableDict, VariationDict, CmabDict
+    from .helpers.types import ExperimentDict, TrafficAllocation, VariableDict, VariationDict, CmabDict
 
 
 class BaseEntity:
@@ -87,7 +87,7 @@ def __init__(
         groupId: Optional[str] = None,
         groupPolicy: Optional[str] = None,
         cmab: Optional[CmabDict] = None,
-        type: Optional[ExperimentType] = None,
+        type: Optional[str] = None,
         **kwargs: Any
     ):
         self.id = id
diff --git a/optimizely/project_config.py b/optimizely/project_config.py
index 3aa1cc2b..5b752538 100644
--- a/optimizely/project_config.py
+++ b/optimizely/project_config.py
@@ -189,24 +189,7 @@ def __init__(self, datafile: str | bytes, logger: Logger, error_handler: Any):
         self.variation_key_map_by_experiment_id: dict[str, dict[str, Union[entities.Variation, VariationDict]]] = {}
         self.flag_variations_map: dict[str, list[entities.Variation]] = {}
 
-        valid_experiment_types = {
-            enums.ExperimentTypes.ab,
-            enums.ExperimentTypes.mab,
-            enums.ExperimentTypes.cmab,
-            enums.ExperimentTypes.td,
-            enums.ExperimentTypes.fr,
-        }
         for experiment in self.experiment_id_map.values():
-            if experiment.type is not None and experiment.type not in valid_experiment_types:
-                self.logger.error(
-                    f'Experiment "{experiment.key}" has invalid type "{experiment.type}". '
-                    f'Valid types: {valid_experiment_types}.'
-                )
-                self.error_handler.handle_error(
-                    exceptions.InvalidExperimentException(
-                        f'Invalid experiment type: {experiment.type}'
-                    )
-                )
             self.experiment_key_map[experiment.key] = experiment
             self.variation_key_map[experiment.key] = self._generate_key_map(
                 experiment.variations, 'key', entities.Variation
diff --git a/tests/test_config.py b/tests/test_config.py
index eba36bc4..c21f9b34 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -1651,6 +1651,41 @@ def test_experiment_type_field_none_when_missing(self):
         experiment = config.experiment_id_map['exp_ab']
         self.assertIsNone(experiment.type)
 
+    def test_unknown_experiment_type_accepted(self):
+        """Test that experiments with unknown type values are accepted without error."""
+        datafile = self._build_datafile(
+            experiments=[
+                {
+                    'id': 'exp_unknown',
+                    'key': 'unknown_type_exp',
+                    'status': 'Running',
+                    'forcedVariations': {},
+                    'layerId': 'layer_1',
+                    'audienceIds': [],
+                    'trafficAllocation': [{'entityId': 'var_1', 'endOfRange': 5000}],
+                    'variations': [{'key': 'var_1', 'id': 'var_1', 'featureEnabled': True}],
+                    'type': 'new_unknown_type',
+                },
+            ],
+            feature_flags=[
+                {
+                    'id': 'flag_1',
+                    'key': 'test_flag',
+                    'experimentIds': ['exp_unknown'],
+                    'rolloutId': '',
+                    'variables': [],
+                },
+            ],
+        )
+
+        opt = optimizely.Optimizely(json.dumps(datafile))
+        config = opt.config_manager.get_config()
+
+        self.assertIsNotNone(config)
+        experiment = config.experiment_id_map['exp_unknown']
+        self.assertEqual(experiment.type, 'new_unknown_type')
+        self.assertEqual(experiment.key, 'unknown_type_exp')
+
     def test_feature_rollout_injects_everyone_else_variation(self):
         """Test that feature_rollout experiments get the everyone else variation injected."""
         datafile = self._build_datafile(