diff --git a/openapi_python_client/parser/properties/__init__.py b/openapi_python_client/parser/properties/__init__.py
index 908745a6a..65dfe42f5 100644
--- a/openapi_python_client/parser/properties/__init__.py
+++ b/openapi_python_client/parser/properties/__init__.py
@@ -352,6 +352,7 @@ def build_union_property(
     *, data: oai.Schema, name: str, required: bool, schemas: Schemas, parent_name: str, config: Config
 ) -> Tuple[Union[UnionProperty, PropertyError], Schemas]:
     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}",
@@ -439,8 +440,8 @@ def _property_from_data(
     if isinstance(data, oai.Reference):
         return _property_from_ref(name=name, required=required, parent=None, data=data, schemas=schemas)
 
+    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)
 
diff --git a/openapi_python_client/parser/properties/model_property.py b/openapi_python_client/parser/properties/model_property.py
index a40460886..7ed00553d 100644
--- a/openapi_python_client/parser/properties/model_property.py
+++ b/openapi_python_client/parser/properties/model_property.py
@@ -88,7 +88,7 @@ def _check_existing(prop: Property) -> Union[Property, PropertyError]:
         return prop_or_error
 
     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..9d95ffe89
--- /dev/null
+++ b/openapi_python_client/schema/openapi_schema_pydantic/callback.py
@@ -0,0 +1,22 @@
+from typing import TYPE_CHECKING, Dict
+
+if TYPE_CHECKING:
+    from .path_item import PathItem
+
+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.
+"""
+
+"""Patterned Fields"""
+
+# {expression}: 'PathItem' = ...
+"""
+A Path Item Object used to define a callback request and expected responses.
+
+A [complete example](../examples/v3.0/callback-example.yaml) is available.
+"""
diff --git a/openapi_python_client/schema/openapi_schema_pydantic/components.py b/openapi_python_client/schema/openapi_schema_pydantic/components.py
index 8ad888906..a9a2f0339 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
@@ -44,7 +45,11 @@ class Components(BaseModel):
     links: Optional[Dict[str, Union[Link, Reference]]] = None
     """An object to hold reusable [Link Objects](#linkObject)."""
 
+    callbacks: Optional[Dict[str, Union[Callback, Reference]]] = None
+    """An object to hold reusable [Callback Objects](#callbackObject)."""
+
     class Config:
+        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 c41aa8406..cbe2fb8eb 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):
@@ -26,6 +26,7 @@ class Contact(BaseModel):
     """
 
     class Config:
+        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 1dfd06a5b..c2deb5a17 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):
@@ -25,6 +25,7 @@ class Discriminator(BaseModel):
     """
 
     class Config:
+        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 9bf2ea177..a9c08a67e 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/encoding.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/encoding.py
@@ -1,9 +1,12 @@
-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:
+    from .header import Header
+
 
 class Encoding(BaseModel):
     """A single encoding definition applied to a single schema property."""
@@ -22,7 +25,7 @@ class Encoding(BaseModel):
     or a comma-separated list of the two types.
     """
 
-    headers: Optional[Dict[str, Reference]] = None
+    headers: Optional[Dict[str, Union["Header", Reference]]] = None
     """
     A map allowing additional information to be provided as headers, for example `Content-Disposition`.
 
@@ -60,6 +63,7 @@ class Encoding(BaseModel):
     """
 
     class Config:
+        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 6da3710b1..4ac234b37 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):
@@ -33,6 +33,7 @@ class Example(BaseModel):
     """
 
     class Config:
+        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 92676a2ae..467c98150 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):
@@ -19,4 +19,5 @@ class ExternalDocumentation(BaseModel):
     """
 
     class Config:
+        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 5e59e8a66..8d6ee2ff1 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
@@ -18,6 +18,7 @@ class Header(Parameter):
     param_in = Field(default=ParameterLocation.HEADER, const=True, alias="in")
 
     class Config:
+        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 36caba733..fcff5b742 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
@@ -47,6 +47,7 @@ class Info(BaseModel):
     """
 
     class Config:
+        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 567a5d117..7e8b7f3d9 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):
@@ -20,4 +20,5 @@ class License(BaseModel):
     """
 
     class Config:
+        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 97bbc8aeb..de1403a8c 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
 
@@ -63,6 +63,7 @@ class Link(BaseModel):
     """
 
     class Config:
+        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 7c00d3bc1..387f33b92 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
@@ -49,6 +49,7 @@ class MediaType(BaseModel):
     """
 
     class Config:
+        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 cdf474bee..7b3c93bfe 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):
@@ -15,7 +15,7 @@ class OAuthFlow(BaseModel):
     This MUST be in the form of a URL.
     """
 
-    tokenUrl: Optional[str] = None
+    tokenUrl: Optional[AnyUrl] = None
     """
     **REQUIRED** for `oauth2 ("password", "clientCredentials", "authorizationCode")`.
     The token URL to be used for this flow.
@@ -35,6 +35,7 @@ class OAuthFlow(BaseModel):
     """
 
     class Config:
+        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 fcb9ba348..e23b3d5dd 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
 
@@ -33,3 +33,6 @@ class OAuthFlows(BaseModel):
 
     Previously called `accessCode` in OpenAPI 2.0.
     """
+
+    class Config:
+        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 dd480a8f5..cbfaa2038 100644
--- a/openapi_python_client/schema/openapi_schema_pydantic/open_api.py
+++ b/openapi_python_client/schema/openapi_schema_pydantic/open_api.py
@@ -1,6 +1,6 @@
 from typing import List, Optional
 
-from pydantic import BaseModel
+from pydantic import BaseModel, Extra
 
 from .components import Components
 from .external_documentation import ExternalDocumentation
@@ -58,3 +58,6 @@ class OpenAPI(BaseModel):
     """
     Additional external documentation.
     """
+
+    class Config:
+        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 860c3c24a..98b2bd2ad 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
@@ -70,6 +71,14 @@ class Operation(BaseModel):
     **REQUIRED**. The list of possible responses as they are returned from executing this operation.
     """
 
+    callbacks: Optional[Dict[str, Callback]] = None
+    """
+    A map of possible out-of band callbacks related to the parent operation.
+    The key is a unique identifier for the Callback Object.
+    Each value in the map is a [Callback Object](#callbackObject)
+    that describes a request that may be initiated by the API provider and the expected responses.
+    """
+
     deprecated: bool = False
     """
     Declares this operation to be deprecated.
@@ -95,6 +104,7 @@ class Operation(BaseModel):
     """
 
     class Config:
+        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 52f1b6885..56070a720 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
@@ -26,7 +26,7 @@ class Parameter(BaseModel):
     - If [`in`](#parameterIn) is `"path"`, the `name` field MUST correspond to a template expression occurring
       within the [path](#pathsPath) field in the [Paths Object](#pathsObject).
       See [Path Templating](#pathTemplating) for further information.
-    - If [`in`](#parameterIn) is `"header"` and the `name` field is `"Accept"`, `"Content-Type"` or `"Authorization"`.
+    - If [`in`](#parameterIn) is `"header"` and the `name` field is `"Accept"`, `"Content-Type"` or `"Authorization"`,
       the parameter definition SHALL be ignored.
     - For all other cases, the `name` corresponds to the parameter name used by the [`in`](#parameterIn) property.
     """
@@ -142,6 +142,7 @@ class Parameter(BaseModel):
     """
 
     class Config:
+        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 911c1e805..cdbd6b564 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
@@ -92,6 +92,7 @@ class PathItem(BaseModel):
     """
 
     class Config:
+        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 7803b3a54..851b28301 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):
@@ -16,6 +16,7 @@ class Reference(BaseModel):
     """**REQUIRED**. The reference string."""
 
     class Config:
+        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 626b795d7..3f7a602d9 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
 
@@ -31,6 +31,7 @@ class RequestBody(BaseModel):
     """
 
     class Config:
+        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 8c8e539ec..24899815e 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
@@ -44,6 +44,7 @@ class Response(BaseModel):
     """
 
     class Config:
+        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 5941d79f5..87492eadc 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
+from pydantic import BaseModel, Extra, Field
 
 from .discriminator import Discriminator
 from .external_documentation import ExternalDocumentation
@@ -224,7 +224,7 @@ class Schema(BaseModel):
     types defined by keyword.  Recall: "number" includes "integer".
     """
 
-    allOf: Optional[List[Union[Reference, "Schema"]]] = None
+    allOf: List[Union[Reference, "Schema"]] = Field(default_factory=list)
     """
     **From OpenAPI spec:
     Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.**
@@ -241,7 +241,7 @@ class Schema(BaseModel):
     value.
     """
 
-    oneOf: List[Union[Reference, "Schema"]] = []
+    oneOf: List[Union[Reference, "Schema"]] = Field(default_factory=list)
     """
     **From OpenAPI spec:
     Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.**
@@ -258,7 +258,7 @@ class Schema(BaseModel):
     keyword's value.
     """
 
-    anyOf: List[Union[Reference, "Schema"]] = []
+    anyOf: List[Union[Reference, "Schema"]] = Field(default_factory=list)
     """
     **From OpenAPI spec:
     Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.**
@@ -472,6 +472,7 @@ class Schema(BaseModel):
     """
 
     class Config:
+        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 aee65bc2b..7bd3b4e8e 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
 
@@ -66,6 +66,7 @@ class SecurityScheme(BaseModel):
     """
 
     class Config:
+        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 43c511f34..949fec8c8 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
 
@@ -31,6 +31,7 @@ class Server(BaseModel):
     """
 
     class Config:
+        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 224c79411..8aa4fac46 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):
@@ -26,3 +26,6 @@ class ServerVariable(BaseModel):
     An optional description for the server variable.
     [CommonMark syntax](https://spec.commonmark.org/) MAY be used for rich text representation.
     """
+
+    class Config:
+        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 531de02b4..1db40d325 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
 
@@ -28,4 +28,5 @@ class Tag(BaseModel):
     """
 
     class Config:
+        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 9ddaf13e3..cfc9c64cb 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):
@@ -48,6 +48,7 @@ class XML(BaseModel):
     """
 
     class Config:
+        extra = Extra.allow
         schema_extra = {
             "examples": [
                 {"namespace": "http://example.com/schema/sample", "prefix": "sample"},