From b818096198cbd7b9a3283d11fee15679947dc50f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebasti=C3=A1n=20Ram=C3=ADrez?= <tiangolo@gmail.com>
Date: Thu, 9 Oct 2025 14:31:55 +0200
Subject: [PATCH] =?UTF-8?q?=E2=99=BB=EF=B8=8F=20Update=20internal=20checks?=
 =?UTF-8?q?=20for=20types=20to=20include=20Pydantic=20v1?=
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---
 fastapi/dependencies/utils.py | 13 +++++++------
 fastapi/utils.py              |  6 +++++-
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/fastapi/dependencies/utils.py b/fastapi/dependencies/utils.py
index e07d1ef88..dc5a06363 100644
--- a/fastapi/dependencies/utils.py
+++ b/fastapi/dependencies/utils.py
@@ -406,9 +406,10 @@ def analyze_param(
             field_info = copy_field_info(
                 field_info=fastapi_annotation, annotation=use_annotation
             )
-            assert (
-                field_info.default is Undefined or field_info.default is RequiredParam
-            ), (
+            assert field_info.default in {
+                Undefined,
+                v1.Undefined,
+            } or field_info.default in {RequiredParam, v1.RequiredParam}, (
                 f"`{field_info.__class__.__name__}` default value cannot be set in"
                 f" `Annotated` for {param_name!r}. Set the default value with `=` instead."
             )
@@ -493,7 +494,7 @@ def analyze_param(
     if field_info is not None:
         # Handle field_info.in_
         if is_path_param:
-            assert isinstance(field_info, params.Path), (
+            assert isinstance(field_info, (params.Path, _params_v1.Path)), (
                 f"Cannot use `{field_info.__class__.__name__}` for path param"
                 f" {param_name!r}"
             )
@@ -819,7 +820,7 @@ def request_params_to_args(
 
     if single_not_embedded_field:
         field_info = first_field.field_info
-        assert isinstance(field_info, params.Param), (
+        assert isinstance(field_info, (params.Param, _params_v1.Param)), (
             "Params must be subclasses of Param"
         )
         loc: Tuple[str, ...] = (field_info.in_.value,)
@@ -831,7 +832,7 @@ def request_params_to_args(
     for field in fields:
         value = _get_multidict_value(field, received_params)
         field_info = field.field_info
-        assert isinstance(field_info, params.Param), (
+        assert isinstance(field_info, (params.Param, _params_v1.Param)), (
             "Params must be subclasses of Param"
         )
         loc = (field_info.in_.value, field.alias)
diff --git a/fastapi/utils.py b/fastapi/utils.py
index 8402d8e19..3ea9271b1 100644
--- a/fastapi/utils.py
+++ b/fastapi/utils.py
@@ -100,7 +100,11 @@ def create_model_field(
         "alias": alias,
     }
 
-    if annotation_is_pydantic_v1(type_) or version == "1":
+    if (
+        annotation_is_pydantic_v1(type_)
+        or isinstance(field_info, v1.FieldInfo)
+        or version == "1"
+    ):
         try:
             return v1.ModelField(**v1_kwargs)  # type: ignore[no-any-return]
         except RuntimeError: