From 17d9be4d3ebed8b3a86683ef49b74a718268d909 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebasti=C3=A1n=20Ram=C3=ADrez?= <tiangolo@gmail.com>
Date: Sun, 21 Dec 2025 16:23:01 +0100
Subject: [PATCH] =?UTF-8?q?=F0=9F=94=8A=20Add=20warnings=20when=20using=20?=
 =?UTF-8?q?Pydantic=20v1?=
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---
 fastapi/dependencies/utils.py |  8 ++++++++
 fastapi/routing.py            | 16 ++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/fastapi/dependencies/utils.py b/fastapi/dependencies/utils.py
index 0ba93524c..39d0bd89c 100644
--- a/fastapi/dependencies/utils.py
+++ b/fastapi/dependencies/utils.py
@@ -1,6 +1,7 @@
 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
@@ -322,6 +323,13 @@ 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,
+            )
         if isinstance(
             param_details.field.field_info, (params.Body, temp_pydantic_v1_params.Body)
         ):
diff --git a/fastapi/routing.py b/fastapi/routing.py
index a1f2e44bb..2770e3253 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -2,6 +2,7 @@ import email.message
 import functools
 import inspect
 import json
+import warnings
 from collections.abc import (
     AsyncIterator,
     Awaitable,
@@ -28,6 +29,7 @@ from fastapi._compat import (
     _get_model_config,
     _model_dump,
     _normalize_errors,
+    annotation_is_pydantic_v1,
     lenient_issubclass,
     may_v1,
 )
@@ -634,6 +636,13 @@ class APIRoute(routing.Route):
                 f"Status code {status_code} must not have a response body"
             )
             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,
+                )
             self.response_field = create_model_field(
                 name=response_name,
                 type_=self.response_model,
@@ -667,6 +676,13 @@ class APIRoute(routing.Route):
                     f"Status code {additional_status_code} must not have a response body"
                 )
                 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,
+                    )
                 response_field = create_model_field(
                     name=response_name, type_=model, mode="serialization"
                 )