diff --git a/openapi_python_client/parser/properties/__init__.py b/openapi_python_client/parser/properties/__init__.py
index 5920987af..524ff5ba0 100644
--- a/openapi_python_client/parser/properties/__init__.py
+++ b/openapi_python_client/parser/properties/__init__.py
@@ -453,6 +453,7 @@ def build_union_property(
             constructed `UnionProperty` or a `PropertyError` describing what went wrong.
     """
     sub_properties: List[Property] = []
+
     for i, sub_prop_data in enumerate(chain(data.anyOf, data.oneOf)):
         sub_prop, schemas = property_from_data(
             name=f"{name}_type_{i}",
@@ -570,8 +571,8 @@ def _property_from_data(
     if isinstance(data, oai.Reference):
         return _property_from_ref(name=name, required=required, parent=None, data=data, schemas=schemas, config=config)
 
+    sub_data: List[Union[oai.Schema, oai.Reference]] = data.allOf + data.anyOf + data.oneOf
     # A union of a single reference should just be passed through to that reference (don't create copy class)
-    sub_data = (data.allOf or []) + data.anyOf + data.oneOf
     if len(sub_data) == 1 and isinstance(sub_data[0], oai.Reference):
         return _property_from_ref(
             name=name, required=required, parent=data, data=sub_data[0], schemas=schemas, config=config
diff --git a/openapi_python_client/parser/properties/model_property.py b/openapi_python_client/parser/properties/model_property.py
index cfaea08b0..6e68a8f8e 100644
--- a/openapi_python_client/parser/properties/model_property.py
+++ b/openapi_python_client/parser/properties/model_property.py
@@ -135,7 +135,7 @@ def _add_if_no_conflict(new_prop: Property) -> Optional[PropertyError]:
         return None
 
     unprocessed_props = data.properties or {}
-    for sub_prop in data.allOf or []:
+    for sub_prop in data.allOf:
         if isinstance(sub_prop, oai.Reference):
             ref_path = parse_reference_path(sub_prop.ref)
             if isinstance(ref_path, ParseError):
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/README.md b/openapi_python_client/schema/openapi_schema_pydantic/README.md
index 0e4d40146..f58b36909 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/README.md
+++ b/openapi_python_client/schema/openapi_schema_pydantic/README.md
@@ -1,5 +1,8 @@
 Everything in this directory (including the rest of this file after this paragraph) is a vendored copy of [openapi-schem-pydantic](https://github.com/kuimono/openapi-schema-pydantic) and is licensed under the LICENSE file in this directory.
 
+Included vendored version is the [following](https://github.com/kuimono/openapi-schema-pydantic/commit/0836b429086917feeb973de3367a7ac4c2b3a665)
+Small patches has been applied to it.
+
 ## Alias
 
 Due to the reserved words in python and pydantic,
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/__init__.py b/openapi_python_client/schema/openapi_schema_pydantic/__init__.py
index 9edb7d3d9..6b02446a8 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/__init__.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/__init__.py
@@ -36,8 +36,11 @@
     "ServerVariable",
     "Tag",
     "XML",
+    "Callback",
 ]
 
+
+from .callback import Callback
 from .components import Components
 from .contact import Contact
 from .discriminator import Discriminator
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/callback.py b/openapi_python_client/schema/openapi_schema_pydantic/callback.py
new file mode 100644
index 000000000..7535cdab8
--- /dev/null
+++ b/openapi_python_client/schema/openapi_schema_pydantic/callback.py
@@ -0,0 +1,15 @@
+from typing import TYPE_CHECKING, Dict
+
+if TYPE_CHECKING:  # pragma: no cover
+    from .path_item import PathItem
+else:
+    PathItem = "PathItem"  # pylint: disable=invalid-name
+
+Callback = Dict[str, PathItem]
+"""
+A map of possible out-of band callbacks related to the parent operation.
+Each value in the map is a [Path Item Object](#pathItemObject)
+that describes a set of requests that may be initiated by the API provider and the expected responses.
+The key value used to identify the path item object is an expression, evaluated at runtime,
+that identifies a URL to use for the callback operation.
+"""
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/components.py b/openapi_python_client/schema/openapi_schema_pydantic/components.py
index 3798a5c13..442b376c1 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/components.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/components.py
@@ -1,7 +1,8 @@
 from typing import Dict, Optional, Union
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
+from .callback import Callback
 from .example import Example
 from .header import Header
 from .link import Link
@@ -32,8 +33,10 @@ class Components(BaseModel):
     headers: Optional[Dict[str, Union[Header, Reference]]] = None
     securitySchemes: Optional[Dict[str, Union[SecurityScheme, Reference]]] = None
     links: Optional[Dict[str, Union[Link, Reference]]] = None
+    callbacks: Optional[Dict[str, Union[Callback, Reference]]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/contact.py b/openapi_python_client/schema/openapi_schema_pydantic/contact.py
index 236548ea9..a02c2638e 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/contact.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/contact.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import AnyUrl, BaseModel
+from pydantic import AnyUrl, BaseModel, Extra
 
 
 class Contact(BaseModel):
@@ -16,6 +16,7 @@ class Contact(BaseModel):
     email: Optional[str] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {"name": "API Support", "url": "http://www.example.com/support", "email": "support@example.com"}
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/discriminator.py b/openapi_python_client/schema/openapi_schema_pydantic/discriminator.py
index 1c84833c9..aa96efa9d 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/discriminator.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/discriminator.py
@@ -1,6 +1,6 @@
 from typing import Dict, Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 
 class Discriminator(BaseModel):
@@ -22,6 +22,7 @@ class Discriminator(BaseModel):
     mapping: Optional[Dict[str, str]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/encoding.py b/openapi_python_client/schema/openapi_schema_pydantic/encoding.py
index 89bec3f00..7497b1650 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/encoding.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/encoding.py
@@ -1,9 +1,14 @@
-from typing import Dict, Optional
+from typing import TYPE_CHECKING, Dict, Optional, Union
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .reference import Reference
 
+if TYPE_CHECKING:  # pragma: no cover
+    from .header import Header
+else:
+    Header = "Header"  # pylint: disable=invalid-name
+
 
 class Encoding(BaseModel):
     """A single encoding definition applied to a single schema property.
@@ -14,12 +19,13 @@ class Encoding(BaseModel):
     """
 
     contentType: Optional[str] = None
-    headers: Optional[Dict[str, Reference]] = None
+    headers: Optional[Dict[str, Union[Header, Reference]]] = None
     style: Optional[str] = None
     explode: bool = False
     allowReserved: bool = False
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/example.py b/openapi_python_client/schema/openapi_schema_pydantic/example.py
index b95df2b62..fdd233f0f 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/example.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/example.py
@@ -1,6 +1,6 @@
 from typing import Any, Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 
 class Example(BaseModel):
@@ -17,6 +17,7 @@ class Example(BaseModel):
     externalValue: Optional[str] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {"summary": "A foo example", "value": {"foo": "bar"}},
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/external_documentation.py b/openapi_python_client/schema/openapi_schema_pydantic/external_documentation.py
index 624a662a9..6f6a27156 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/external_documentation.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/external_documentation.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import AnyUrl, BaseModel
+from pydantic import AnyUrl, BaseModel, Extra
 
 
 class ExternalDocumentation(BaseModel):
@@ -14,4 +14,5 @@ class ExternalDocumentation(BaseModel):
     url: AnyUrl
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {"examples": [{"description": "Find more info here", "url": "https://example.com"}]}
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/header.py b/openapi_python_client/schema/openapi_schema_pydantic/header.py
index 69200a7fa..a3eb731e2 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/header.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/header.py
@@ -1,4 +1,4 @@
-from pydantic import Field
+from pydantic import Extra, Field
 
 from ..parameter_location import ParameterLocation
 from .parameter import Parameter
@@ -22,6 +22,7 @@ class Header(Parameter):
     param_in = Field(default=ParameterLocation.HEADER, const=True, alias="in")
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         allow_population_by_field_name = True
         schema_extra = {
             "examples": [
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/info.py b/openapi_python_client/schema/openapi_schema_pydantic/info.py
index ea5337f50..2c87c8605 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/info.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/info.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import AnyUrl, BaseModel
+from pydantic import AnyUrl, BaseModel, Extra
 
 from .contact import Contact
 from .license import License
@@ -25,6 +25,7 @@ class Info(BaseModel):
     version: str
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/license.py b/openapi_python_client/schema/openapi_schema_pydantic/license.py
index ca40f1ac5..d055eb902 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/license.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/license.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import AnyUrl, BaseModel
+from pydantic import AnyUrl, BaseModel, Extra
 
 
 class License(BaseModel):
@@ -15,4 +15,5 @@ class License(BaseModel):
     url: Optional[AnyUrl] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {"examples": [{"name": "Apache 2.0", "url": "https://www.apache.org/licenses/LICENSE-2.0.html"}]}
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/link.py b/openapi_python_client/schema/openapi_schema_pydantic/link.py
index 965508123..162938d3d 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/link.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/link.py
@@ -1,6 +1,6 @@
 from typing import Any, Dict, Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .server import Server
 
@@ -31,6 +31,7 @@ class Link(BaseModel):
     server: Optional[Server] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {"operationId": "getUserAddressByUUID", "parameters": {"userUuid": "$response.body#/uuid"}},
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/media_type.py b/openapi_python_client/schema/openapi_schema_pydantic/media_type.py
index e4eb4542a..851ca3462 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/media_type.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/media_type.py
@@ -1,6 +1,6 @@
 from typing import Any, Dict, Optional, Union
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Extra, Field
 
 from .encoding import Encoding
 from .example import Example
@@ -22,6 +22,7 @@ class MediaType(BaseModel):
     encoding: Optional[Dict[str, Encoding]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         allow_population_by_field_name = True
         schema_extra = {
             "examples": [
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/oauth_flow.py b/openapi_python_client/schema/openapi_schema_pydantic/oauth_flow.py
index 09a170acb..32c70e351 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/oauth_flow.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/oauth_flow.py
@@ -1,6 +1,6 @@
 from typing import Dict, Optional
 
-from pydantic import AnyUrl, BaseModel
+from pydantic import AnyUrl, BaseModel, Extra
 
 
 class OAuthFlow(BaseModel):
@@ -13,11 +13,12 @@ class OAuthFlow(BaseModel):
     """
 
     authorizationUrl: Optional[AnyUrl] = None
-    tokenUrl: Optional[str] = None
+    tokenUrl: Optional[AnyUrl] = None
     refreshUrl: Optional[AnyUrl] = None
     scopes: Dict[str, str]
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/oauth_flows.py b/openapi_python_client/schema/openapi_schema_pydantic/oauth_flows.py
index 2e363aac6..4f9c739d4 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/oauth_flows.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/oauth_flows.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .oauth_flow import OAuthFlow
 
@@ -18,3 +18,6 @@ class OAuthFlows(BaseModel):
     password: Optional[OAuthFlow] = None
     clientCredentials: Optional[OAuthFlow] = None
     authorizationCode: Optional[OAuthFlow] = None
+
+    class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/open_api.py b/openapi_python_client/schema/openapi_schema_pydantic/open_api.py
index 9c1dfcbf4..50fdebd5e 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/open_api.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/open_api.py
@@ -2,7 +2,7 @@
 import sys
 from typing import List, Optional, Union
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .components import Components
 from .external_documentation import ExternalDocumentation
@@ -34,3 +34,6 @@ class OpenAPI(BaseModel):
     tags: Optional[List[Tag]] = None
     externalDocs: Optional[ExternalDocumentation] = None
     openapi: 'Union[Literal["3.0.0"], Literal["3.0.1"], Literal["3.0.2"], Literal["3.0.3"]]'
+
+    class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/operation.py b/openapi_python_client/schema/openapi_schema_pydantic/operation.py
index 06fea6936..19c78c6d5 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/operation.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/operation.py
@@ -1,7 +1,8 @@
-from typing import List, Optional, Union
+from typing import Dict, List, Optional, Union
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
+from .callback import Callback
 from .external_documentation import ExternalDocumentation
 from .parameter import Parameter
 from .reference import Reference
@@ -27,11 +28,14 @@ class Operation(BaseModel):
     parameters: Optional[List[Union[Parameter, Reference]]] = None
     requestBody: Optional[Union[RequestBody, Reference]] = None
     responses: Responses
+    callbacks: Optional[Dict[str, Callback]] = None
+
     deprecated: bool = False
     security: Optional[List[SecurityRequirement]] = None
     servers: Optional[List[Server]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/parameter.py b/openapi_python_client/schema/openapi_schema_pydantic/parameter.py
index 4bf99185d..cf883a9d2 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/parameter.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/parameter.py
@@ -1,6 +1,6 @@
 from typing import Any, Dict, Optional, Union
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Extra, Field
 
 from ..parameter_location import ParameterLocation
 from .example import Example
@@ -36,6 +36,7 @@ class Parameter(BaseModel):
     content: Optional[Dict[str, MediaType]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         allow_population_by_field_name = True
         schema_extra = {
             "examples": [
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/path_item.py b/openapi_python_client/schema/openapi_schema_pydantic/path_item.py
index d0b3598dd..af1a1a6a3 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/path_item.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/path_item.py
@@ -1,6 +1,6 @@
 from typing import List, Optional, Union
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Extra, Field
 
 from .operation import Operation
 from .parameter import Parameter
@@ -35,6 +35,7 @@ class PathItem(BaseModel):
     parameters: Optional[List[Union[Parameter, Reference]]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         allow_population_by_field_name = True
         schema_extra = {
             "examples": [
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/reference.py b/openapi_python_client/schema/openapi_schema_pydantic/reference.py
index ad21a2fe0..3e99d0d8e 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/reference.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/reference.py
@@ -1,4 +1,4 @@
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Extra, Field
 
 
 class Reference(BaseModel):
@@ -19,6 +19,7 @@ class Reference(BaseModel):
     ref: str = Field(alias="$ref")
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         allow_population_by_field_name = True
         schema_extra = {
             "examples": [{"$ref": "#/components/schemas/Pet"}, {"$ref": "Pet.json"}, {"$ref": "definitions.json#/Pet"}]
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/request_body.py b/openapi_python_client/schema/openapi_schema_pydantic/request_body.py
index 1b0df2ea3..60b5cda5d 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/request_body.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/request_body.py
@@ -1,6 +1,6 @@
 from typing import Dict, Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .media_type import MediaType
 
@@ -18,6 +18,7 @@ class RequestBody(BaseModel):
     required: bool = False
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/response.py b/openapi_python_client/schema/openapi_schema_pydantic/response.py
index a8723b124..a690ebebb 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/response.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/response.py
@@ -1,6 +1,6 @@
 from typing import Dict, Optional, Union
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .header import Header
 from .link import Link
@@ -24,6 +24,7 @@ class Response(BaseModel):
     links: Optional[Dict[str, Union[Link, Reference]]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/schema.py b/openapi_python_client/schema/openapi_schema_pydantic/schema.py
index bfd0b2719..f8cfa51e8 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/schema.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/schema.py
@@ -1,6 +1,6 @@
 from typing import Any, Dict, List, Optional, Union
 
-from pydantic import BaseModel, Field, StrictInt, StrictStr
+from pydantic import BaseModel, Extra, Field, StrictInt, StrictStr
 
 from ..data_type import DataType
 from .discriminator import Discriminator
@@ -37,9 +37,9 @@ class Schema(BaseModel):
     required: Optional[List[str]] = Field(default=None, min_items=1)
     enum: Union[None, List[Optional[StrictInt]], List[Optional[StrictStr]]] = Field(default=None, min_items=1)
     type: Optional[DataType] = Field(default=None)
-    allOf: Optional[List[Union[Reference, "Schema"]]] = None
-    oneOf: List[Union[Reference, "Schema"]] = []
-    anyOf: List[Union[Reference, "Schema"]] = []
+    allOf: List[Union[Reference, "Schema"]] = Field(default_factory=list)
+    oneOf: List[Union[Reference, "Schema"]] = Field(default_factory=list)
+    anyOf: List[Union[Reference, "Schema"]] = Field(default_factory=list)
     schema_not: Optional[Union[Reference, "Schema"]] = Field(default=None, alias="not")
     items: Optional[Union[Reference, "Schema"]] = None
     properties: Optional[Dict[str, Union[Reference, "Schema"]]] = None
@@ -57,6 +57,7 @@ class Schema(BaseModel):
     deprecated: Optional[bool] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         allow_population_by_field_name = True
         schema_extra = {
             "examples": [
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/security_scheme.py b/openapi_python_client/schema/openapi_schema_pydantic/security_scheme.py
index 25ee2df8f..1e16ffcdc 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/security_scheme.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/security_scheme.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import AnyUrl, BaseModel, Field
+from pydantic import AnyUrl, BaseModel, Extra, Field
 
 from .oauth_flows import OAuthFlows
 
@@ -29,6 +29,7 @@ class SecurityScheme(BaseModel):
     openIdConnectUrl: Optional[AnyUrl] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         allow_population_by_field_name = True
         schema_extra = {
             "examples": [
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/server.py b/openapi_python_client/schema/openapi_schema_pydantic/server.py
index 9a37b566a..3850cea0f 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/server.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/server.py
@@ -1,6 +1,6 @@
 from typing import Dict, Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .server_variable import ServerVariable
 
@@ -18,6 +18,7 @@ class Server(BaseModel):
     variables: Optional[Dict[str, ServerVariable]] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {"url": "https://development.gigantic-server.com/v1", "description": "Development server"},
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/server_variable.py b/openapi_python_client/schema/openapi_schema_pydantic/server_variable.py
index f6286f883..5a51b50da 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/server_variable.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/server_variable.py
@@ -1,6 +1,6 @@
 from typing import List, Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 
 class ServerVariable(BaseModel):
@@ -14,3 +14,6 @@ class ServerVariable(BaseModel):
     enum: Optional[List[str]] = None
     default: str
     description: Optional[str] = None
+
+    class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/tag.py b/openapi_python_client/schema/openapi_schema_pydantic/tag.py
index cf112fc47..e4ff5f362 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/tag.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/tag.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .external_documentation import ExternalDocumentation
 
@@ -20,4 +20,5 @@ class Tag(BaseModel):
     externalDocs: Optional[ExternalDocumentation] = None
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {"examples": [{"name": "pet", "description": "Pets operations"}]}
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/xml.py b/openapi_python_client/schema/openapi_schema_pydantic/xml.py
index ddb0e7205..bc6106222 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/xml.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/xml.py
@@ -1,6 +1,6 @@
 from typing import Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 
 class XML(BaseModel):
@@ -23,6 +23,7 @@ class XML(BaseModel):
     wrapped: bool = False
 
     class Config:  # pylint: disable=missing-class-docstring
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {"namespace": "http://example.com/schema/sample", "prefix": "sample"},