diff --git a/src/curies/api.py b/src/curies/api.py
index 7e8e024..053f6e1 100644
--- a/src/curies/api.py
+++ b/src/curies/api.py
@@ -36,7 +36,10 @@
 from pydantic import BaseModel, Field
 from pytrie import StringTrie
 
-from ._pydantic_compat import field_validator, get_field_validator_values
+from ._pydantic_compat import PYDANTIC_V1, field_validator, get_field_validator_values
+
+if not PYDANTIC_V1:
+    from pydantic import ConfigDict
 
 if TYPE_CHECKING:  # pragma: no cover
     import pandas
@@ -201,10 +204,15 @@ class notion of parsed reference (instead of merely stringified
         ..., description="The local unique identifier used in a compact URI (CURIE)."
     )
 
-    class Config:
-        """Pydantic configuration for references."""
+    if PYDANTIC_V1:
+
+        class Config:
+            """Pydantic configuration for references."""
 
-        frozen = True
+            frozen = True
+
+    else:
+        model_config = ConfigDict(frozen=True)
 
     @property
     def curie(self) -> str: