From 4b0fca4cbdc6ba6555259dd6e4d2807da6568588 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebasti=C3=A1n=20Ram=C3=ADrez?= <tiangolo@gmail.com>
Date: Thu, 25 Dec 2025 12:05:51 +0100
Subject: [PATCH] =?UTF-8?q?=E2=99=BB=EF=B8=8F=20Error=20out=20when=20using?=
 =?UTF-8?q?=20pydantic.v1?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 fastapi/dependencies/utils.py | 11 ++++-------
 fastapi/exceptions.py         |  6 ++++++
 fastapi/routing.py            | 18 +++++++-----------
 3 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/fastapi/dependencies/utils.py b/fastapi/dependencies/utils.py
index 39d0bd89c..2cebae618 100644
--- a/fastapi/dependencies/utils.py
+++ b/fastapi/dependencies/utils.py
@@ -1,7 +1,6 @@
 import dataclasses
 import inspect
 import sys
-import warnings
 from collections.abc import Coroutine, Mapping, Sequence
 from contextlib import AsyncExitStack, contextmanager
 from copy import copy, deepcopy
@@ -51,7 +50,7 @@ from fastapi.concurrency import (
     contextmanager_in_threadpool,
 )
 from fastapi.dependencies.models import Dependant
-from fastapi.exceptions import DependencyScopeError
+from fastapi.exceptions import DependencyScopeError, PydanticV1NotSupportedError
 from fastapi.logger import logger
 from fastapi.security.oauth2 import SecurityScopes
 from fastapi.types import DependencyCacheKey
@@ -324,11 +323,9 @@ def get_dependant(
             continue
         assert param_details.field is not None
         if isinstance(param_details.field, may_v1.ModelField):
-            warnings.warn(
-                "pydantic.v1 is deprecated and will soon stop being supported by FastAPI."
-                f" Please update the param {param_name}: {param_details.type_annotation!r}.",
-                category=DeprecationWarning,
-                stacklevel=5,
+            raise PydanticV1NotSupportedError(
+                "pydantic.v1 models are no longer supported by FastAPI."
+                f" Please update the param {param_name}: {param_details.type_annotation!r}."
             )
         if isinstance(
             param_details.field.field_info, (params.Body, temp_pydantic_v1_params.Body)
diff --git a/fastapi/exceptions.py b/fastapi/exceptions.py
index 8e0c55902..a133cd793 100644
--- a/fastapi/exceptions.py
+++ b/fastapi/exceptions.py
@@ -231,3 +231,9 @@ class ResponseValidationError(ValidationException):
     ) -> None:
         super().__init__(errors, endpoint_ctx=endpoint_ctx)
         self.body = body
+
+
+class PydanticV1NotSupportedError(FastAPIError):
+    """
+    A pydantic.v1 model is used, which is no longer supported.
+    """
diff --git a/fastapi/routing.py b/fastapi/routing.py
index 2770e3253..fc3fb33d4 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -2,7 +2,6 @@ import email.message
 import functools
 import inspect
 import json
-import warnings
 from collections.abc import (
     AsyncIterator,
     Awaitable,
@@ -48,6 +47,7 @@ from fastapi.encoders import jsonable_encoder
 from fastapi.exceptions import (
     EndpointContext,
     FastAPIError,
+    PydanticV1NotSupportedError,
     RequestValidationError,
     ResponseValidationError,
     WebSocketRequestValidationError,
@@ -637,11 +637,9 @@ class APIRoute(routing.Route):
             )
             response_name = "Response_" + self.unique_id
             if annotation_is_pydantic_v1(self.response_model):
-                warnings.warn(
-                    "pydantic.v1 is deprecated and will soon stop being supported by FastAPI."
-                    f" Please update the response model {self.response_model!r}.",
-                    category=DeprecationWarning,
-                    stacklevel=4,
+                raise PydanticV1NotSupportedError(
+                    "pydantic.v1 models are no longer supported by FastAPI."
+                    f" Please update the response model {self.response_model!r}."
                 )
             self.response_field = create_model_field(
                 name=response_name,
@@ -677,11 +675,9 @@ class APIRoute(routing.Route):
                 )
                 response_name = f"Response_{additional_status_code}_{self.unique_id}"
                 if annotation_is_pydantic_v1(model):
-                    warnings.warn(
-                        "pydantic.v1 is deprecated and will soon stop being supported by FastAPI."
-                        f" In responses={{}}, please update {model}.",
-                        category=DeprecationWarning,
-                        stacklevel=4,
+                    raise PydanticV1NotSupportedError(
+                        "pydantic.v1 models are no longer supported by FastAPI."
+                        f" In responses={{}}, please update {model}."
                     )
                 response_field = create_model_field(
                     name=response_name, type_=model, mode="serialization"