diff --git a/pyproject.toml b/pyproject.toml
index 49ef87f..08565a8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "uncertainty-engine-types"
-version = "0.20.0"
+version = "0.21.0"
 description = "Common type definitions for the Uncertainty Engine"
 authors = [
     { name = "Freddy Wordingham", email = "freddy@digilab.ai" },
diff --git a/uncertainty_engine_types/model_config.py b/uncertainty_engine_types/model_config.py
index 69f2b2f..bdf713a 100644
--- a/uncertainty_engine_types/model_config.py
+++ b/uncertainty_engine_types/model_config.py
@@ -9,7 +9,7 @@
 ]
 
 
-class ModelConfig(BaseModel):
+class ModelConfig(BaseModel, extra="forbid"):
     custom_config: Literal[False] = False
     input_variance: Optional[float] = None
     input_retained_dimensions: Optional[int] = None
diff --git a/uncertainty_engine_types/version.py b/uncertainty_engine_types/version.py
index 5f4bb0b..6a726d8 100644
--- a/uncertainty_engine_types/version.py
+++ b/uncertainty_engine_types/version.py
@@ -1 +1 @@
-__version__ = "0.20.0"
+__version__ = "0.21.0"