diff --git a/fastapi/_compat/main.py b/fastapi/_compat/main.py
index 3f758f072..777f93d61 100644
--- a/fastapi/_compat/main.py
+++ b/fastapi/_compat/main.py
@@ -3,6 +3,7 @@ from typing import (
     Any,
     Dict,
     List,
+    Optional,
     Sequence,
     Tuple,
     Type,
@@ -19,6 +20,7 @@ from .model_field import ModelField
 if PYDANTIC_V2:
     from .v2 import BaseConfig as BaseConfig
     from .v2 import FieldInfo as FieldInfo
+    from .v2 import GenerateJsonSchema
     from .v2 import PydanticSchemaGenerationError as PydanticSchemaGenerationError
     from .v2 import RequiredParam as RequiredParam
     from .v2 import Undefined as Undefined
@@ -33,6 +35,7 @@ if PYDANTIC_V2:
 else:
     from .v1 import BaseConfig as BaseConfig  # type: ignore[assignment]
     from .v1 import FieldInfo as FieldInfo
+    from .v1 import GenerateJsonSchema
     from .v1 import (  # type: ignore[assignment]
         PydanticSchemaGenerationError as PydanticSchemaGenerationError,
     )
@@ -231,6 +234,7 @@ def get_definitions(
     fields: List[ModelField],
     model_name_map: ModelNameMap,
     separate_input_output_schemas: bool = True,
+    schema_generator: Optional[GenerateJsonSchema] = None,
 ) -> Tuple[
     Dict[Tuple[ModelField, Literal["validation", "serialization"]], v1.JsonSchemaValue],
     Dict[str, Dict[str, Any]],
@@ -251,6 +255,7 @@ def get_definitions(
             fields=v2_fields,
             model_name_map=model_name_map,
             separate_input_output_schemas=separate_input_output_schemas,
+            schema_generator=schema_generator,
         )
         all_definitions = {**v1_definitions, **v2_definitions}
         all_field_maps = {**v1_field_maps, **v2_field_maps}
diff --git a/fastapi/_compat/v2.py b/fastapi/_compat/v2.py
index 29606b9f3..aea7037b3 100644
--- a/fastapi/_compat/v2.py
+++ b/fastapi/_compat/v2.py
@@ -7,6 +7,7 @@ from typing import (
     Any,
     Dict,
     List,
+    Optional,
     Sequence,
     Set,
     Tuple,
@@ -199,11 +200,12 @@ def get_definitions(
     fields: Sequence[ModelField],
     model_name_map: ModelNameMap,
     separate_input_output_schemas: bool = True,
+    schema_generator: Optional[GenerateJsonSchema] = None,
 ) -> Tuple[
     Dict[Tuple[ModelField, Literal["validation", "serialization"]], JsonSchemaValue],
     Dict[str, Dict[str, Any]],
 ]:
-    schema_generator = GenerateJsonSchema(ref_template=REF_TEMPLATE)
+    schema_generator = schema_generator or GenerateJsonSchema(ref_template=REF_TEMPLATE)
     override_mode: Union[Literal["validation"], None] = (
         None if separate_input_output_schemas else "validation"
     )
diff --git a/fastapi/openapi/utils.py b/fastapi/openapi/utils.py
index dbc93d289..d006c8586 100644
--- a/fastapi/openapi/utils.py
+++ b/fastapi/openapi/utils.py
@@ -5,6 +5,7 @@ from typing import Any, Dict, List, Optional, Sequence, Set, Tuple, Type, Union,
 
 from fastapi import routing
 from fastapi._compat import (
+    PYDANTIC_V2,
     JsonSchemaValue,
     ModelField,
     Undefined,
@@ -38,6 +39,11 @@ from typing_extensions import Literal
 
 from .._compat import _is_model_field
 
+if PYDANTIC_V2:
+    from .._compat.v2 import GenerateJsonSchema
+else:
+    from .._compat.v1 import GenerateJsonSchema
+
 validation_error_definition = {
     "title": "ValidationError",
     "type": "object",
@@ -480,6 +486,7 @@ def get_openapi(
     license_info: Optional[Dict[str, Union[str, Any]]] = None,
     separate_input_output_schemas: bool = True,
     external_docs: Optional[Dict[str, Any]] = None,
+    schema_generator: Optional[GenerateJsonSchema] = None,
 ) -> Dict[str, Any]:
     info: Dict[str, Any] = {"title": title, "version": version}
     if summary:
@@ -505,6 +512,7 @@ def get_openapi(
         fields=all_fields,
         model_name_map=model_name_map,
         separate_input_output_schemas=separate_input_output_schemas,
+        schema_generator=schema_generator,
     )
     for route in routes or []:
         if isinstance(route, routing.APIRoute):