[Core] add deprecation warning for pydantic v1 (#59703)

related to #58876

```bash
❯ python -c "
import ray
# Temporarily patch to test the warning shows
from ray._common import pydantic_compat
original = pydantic_compat.IS_PYDANTIC_2
pydantic_compat.IS_PYDANTIC_2 = False  # Simulate Pydantic v1

ray.init()
ray.shutdown()

pydantic_compat.IS_PYDANTIC_2 = original
"
2025-12-26 22:33:01,387 INFO worker.py:1811 -- Connecting to existing Ray cluster at address: 172.31.7.228:6379...
2025-12-26 22:33:01,407 INFO worker.py:1991 -- Connected to Ray cluster. View the dashboard at 127.0.0.1:8265 
/home/ubuntu/ray/python/ray/_private/worker.py:2039: FutureWarning: Tip: In future versions of Ray, Ray will no longer override accelerator visible devices env var if num_gpus=0 or num_gpus=None (default). To enable this behavior and turn off this error message, set RAY_ACCEL_ENV_VAR_OVERRIDE_ON_ZERO=0
  warnings.warn(
/home/ubuntu/ray/python/ray/_private/worker.py:2050: FutureWarning: Pydantic v1 is deprecated and will no longer be supported in Ray 2.56. Please upgrade to Pydantic v2 by running `pip install -U pydantic`. See #58876 for more details.
  warnings.warn(
 ~/ray │ on 58876-abrar-pydantic *91       
"
```

---------

Signed-off-by: abrar <abrar@anyscale.com>

Author: abrarsheikh

doc/source/ray-overview/installation.rst

@@ -13,6 +13,11 @@ Installing Ray
 Ray currently officially supports x86_64, aarch64 (ARM) for Linux, and Apple silicon (M1) hardware.
 Ray on Windows is currently in beta.
 
+.. warning::
+   **Pydantic v1 Deprecation Notice:** Pydantic v1 is deprecated and Ray will drop support for it in
+   version 2.56. If you're using Pydantic v1, upgrade to Pydantic v2 by running ``pip install -U pydantic``.
+   See `GitHub issue #58876 <https://github.com/ray-project/ray/issues/58876>`_ for more details.
+
 Official Releases
 -----------------
 

doc/source/serve/advanced-guides/app-builder-guide.md

@@ -77,6 +77,10 @@ Notice that the "Hello from config" message is printed from within the deploymen
 (typed-app-builders)=
 ### Typing arguments with Pydantic
 
+:::{warning}
+**Pydantic v1 Deprecation Notice:** Pydantic v1 is deprecated and Ray will drop support for it in version 2.56. If you're using Pydantic v1, upgrade to Pydantic v2 by running `pip install -U pydantic`. See [GitHub issue #58876](https://github.com/ray-project/ray/issues/58876) for more details.
+:::
+
 To avoid writing logic to parse and validate the arguments by hand, define a [Pydantic model](https://pydantic-docs.helpmanual.io/usage/models/) as the single input parameter's type to your application builder function (the parameter must be type annotated).
 Arguments are passed the same way, but the resulting dictionary is used to construct the Pydantic model using `model.parse_obj(args_dict)`.
 

python/ray/_common/pydantic_compat.py

@@ -1,4 +1,5 @@
 # ruff: noqa
+from typing import Optional
 import packaging.version
 
 # Pydantic is a dependency of `ray["default"]` but not the minimal installation,
@@ -12,6 +13,13 @@
     PYDANTIC_INSTALLED = False
 
 
+PYDANTIC_MAJOR_VERSION: Optional[int] = (
+    packaging.version.parse(pydantic.__version__).major
+    if PYDANTIC_INSTALLED and hasattr(pydantic, "__version__")
+    else None
+)
+
+
 if not PYDANTIC_INSTALLED:
     IS_PYDANTIC_2 = False
     BaseModel = None

python/ray/_private/worker.py

@@ -2044,6 +2044,21 @@ def sigterm_handler(signum, frame):
             FutureWarning,
         )
 
+    # Check for Pydantic v1 and emit deprecation warning
+    from ray._common.pydantic_compat import PYDANTIC_MAJOR_VERSION
+
+    if (
+        PYDANTIC_MAJOR_VERSION
+        and PYDANTIC_MAJOR_VERSION == 1
+        and log_once("pydantic_v1_deprecation")
+    ):
+        warnings.warn(
+            "Pydantic v1 is deprecated and will no longer be supported in Ray 2.56. "
+            "Please upgrade to Pydantic v2 by running `pip install pydantic>=2`. "
+            "See https://github.com/ray-project/ray/issues/58876 for more details.",
+            FutureWarning,
+        )
+
     node_id = global_worker.core_worker.get_current_node_id()
     global_node_address_info = _global_node.address_info.copy()
     global_node_address_info["webui_url"] = _remove_protocol_from_url(dashboard_url)