diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bc3b2d2d..b438aafe 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -63,7 +63,7 @@ jobs:
       - name: Get GitHub OIDC Token
         if: github.repository == 'stainless-sdks/kernel-python'
         id: github-oidc
-        uses: actions/github-script@v6
+        uses: actions/github-script@v8
         with:
           script: core.setOutput('github_token', await core.getIDToken());
 
diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 8935e932..b8dda9bf 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "0.28.0"
+  ".": "0.29.0"
 }
\ No newline at end of file
diff --git a/.stats.yml b/.stats.yml
index bcbec15d..470e4983 100644
--- a/.stats.yml
+++ b/.stats.yml
@@ -1,4 +1,4 @@
 configured_endpoints: 97
-openapi_spec_url: https://storage.googleapis.com/stainless-sdk-openapi-specs/kernel%2Fkernel-d430a8e3407ceb608d912cabadbcb016b4fcf057ca56b3bbd179ea3b3121b484.yml
-openapi_spec_hash: 8adbf013baf77abacaf04ed067749397
+openapi_spec_url: https://storage.googleapis.com/stainless-sdk-openapi-specs/kernel%2Fkernel-46c8320dcd9f8fc596f469ef0dd1aafaca591ab36cf2a6f8a7297dc9136bdc71.yml
+openapi_spec_hash: 1be1e6589cd94c581b241720e01a65bc
 config_hash: b470456b217bb9502f5212311d395a6f
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1b162d16..1f736cba 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,19 @@
 # Changelog
 
+## 0.29.0 (2026-01-30)
+
+Full Changelog: [v0.28.0...v0.29.0](https://github.com/kernel/kernel-python-sdk/compare/v0.28.0...v0.29.0)
+
+### Features
+
+* add support for 1280x800@60 viewport ([1cb6575](https://github.com/kernel/kernel-python-sdk/commit/1cb65752f6aa45fcb2ca1dd55f0eebf9457abfa9))
+* **client:** add custom JSON encoder for extended type support ([33604fe](https://github.com/kernel/kernel-python-sdk/commit/33604feb1a07bbca94477c28143052d5c6eff70d))
+
+
+### Chores
+
+* **ci:** upgrade `actions/github-script` ([4828aba](https://github.com/kernel/kernel-python-sdk/commit/4828aba4349e61686285b57358892825e75286be))
+
 ## 0.28.0 (2026-01-22)
 
 Full Changelog: [v0.27.0...v0.28.0](https://github.com/kernel/kernel-python-sdk/compare/v0.27.0...v0.28.0)
diff --git a/pyproject.toml b/pyproject.toml
index 4402e482..66433700 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "kernel"
-version = "0.28.0"
+version = "0.29.0"
 description = "The official Python library for the kernel API"
 dynamic = ["readme"]
 license = "Apache-2.0"
diff --git a/src/kernel/_base_client.py b/src/kernel/_base_client.py
index 07809c5b..a3d47eaf 100644
--- a/src/kernel/_base_client.py
+++ b/src/kernel/_base_client.py
@@ -86,6 +86,7 @@
     APIConnectionError,
     APIResponseValidationError,
 )
+from ._utils._json import openapi_dumps
 
 log: logging.Logger = logging.getLogger(__name__)
 
@@ -554,8 +555,10 @@ def _build_request(
                 kwargs["content"] = options.content
             elif isinstance(json_data, bytes):
                 kwargs["content"] = json_data
-            else:
-                kwargs["json"] = json_data if is_given(json_data) else None
+            elif not files:
+                # Don't set content when JSON is sent as multipart/form-data,
+                # since httpx's content param overrides other body arguments
+                kwargs["content"] = openapi_dumps(json_data) if is_given(json_data) and json_data is not None else None
             kwargs["files"] = files
         else:
             headers.pop("Content-Type", None)
diff --git a/src/kernel/_compat.py b/src/kernel/_compat.py
index bdef67f0..786ff42a 100644
--- a/src/kernel/_compat.py
+++ b/src/kernel/_compat.py
@@ -139,6 +139,7 @@ def model_dump(
     exclude_defaults: bool = False,
     warnings: bool = True,
     mode: Literal["json", "python"] = "python",
+    by_alias: bool | None = None,
 ) -> dict[str, Any]:
     if (not PYDANTIC_V1) or hasattr(model, "model_dump"):
         return model.model_dump(
@@ -148,13 +149,12 @@ def model_dump(
             exclude_defaults=exclude_defaults,
             # warnings are not supported in Pydantic v1
             warnings=True if PYDANTIC_V1 else warnings,
+            by_alias=by_alias,
         )
     return cast(
         "dict[str, Any]",
         model.dict(  # pyright: ignore[reportDeprecated, reportUnnecessaryCast]
-            exclude=exclude,
-            exclude_unset=exclude_unset,
-            exclude_defaults=exclude_defaults,
+            exclude=exclude, exclude_unset=exclude_unset, exclude_defaults=exclude_defaults, by_alias=bool(by_alias)
         ),
     )
 
diff --git a/src/kernel/_utils/_json.py b/src/kernel/_utils/_json.py
new file mode 100644
index 00000000..60584214
--- /dev/null
+++ b/src/kernel/_utils/_json.py
@@ -0,0 +1,35 @@
+import json
+from typing import Any
+from datetime import datetime
+from typing_extensions import override
+
+import pydantic
+
+from .._compat import model_dump
+
+
+def openapi_dumps(obj: Any) -> bytes:
+    """
+    Serialize an object to UTF-8 encoded JSON bytes.
+
+    Extends the standard json.dumps with support for additional types
+    commonly used in the SDK, such as `datetime`, `pydantic.BaseModel`, etc.
+    """
+    return json.dumps(
+        obj,
+        cls=_CustomEncoder,
+        # Uses the same defaults as httpx's JSON serialization
+        ensure_ascii=False,
+        separators=(",", ":"),
+        allow_nan=False,
+    ).encode()
+
+
+class _CustomEncoder(json.JSONEncoder):
+    @override
+    def default(self, o: Any) -> Any:
+        if isinstance(o, datetime):
+            return o.isoformat()
+        if isinstance(o, pydantic.BaseModel):
+            return model_dump(o, exclude_unset=True, mode="json", by_alias=True)
+        return super().default(o)
diff --git a/src/kernel/_version.py b/src/kernel/_version.py
index f78bed97..d24a1a6c 100644
--- a/src/kernel/_version.py
+++ b/src/kernel/_version.py
@@ -1,4 +1,4 @@
 # File generated from our OpenAPI spec by Stainless. See CONTRIBUTING.md for details.
 
 __title__ = "kernel"
-__version__ = "0.28.0"  # x-release-please-version
+__version__ = "0.29.0"  # x-release-please-version
diff --git a/src/kernel/resources/browser_pools.py b/src/kernel/resources/browser_pools.py
index 884b0e16..4f6ad8b2 100644
--- a/src/kernel/resources/browser_pools.py
+++ b/src/kernel/resources/browser_pools.py
@@ -111,8 +111,8 @@ def create(
               image defaults apply (1920x1080@25). Only specific viewport configurations are
               supported. The server will reject unsupported combinations. Supported
               resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25,
-              1024x768@60, 1200x800@60 If refresh_rate is not provided, it will be
-              automatically determined from the width and height if they match a supported
+              1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
+              be automatically determined from the width and height if they match a supported
               configuration exactly. Note: Higher resolutions may affect the responsiveness of
               live view browser
 
@@ -243,8 +243,8 @@ def update(
               image defaults apply (1920x1080@25). Only specific viewport configurations are
               supported. The server will reject unsupported combinations. Supported
               resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25,
-              1024x768@60, 1200x800@60 If refresh_rate is not provided, it will be
-              automatically determined from the width and height if they match a supported
+              1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
+              be automatically determined from the width and height if they match a supported
               configuration exactly. Note: Higher resolutions may affect the responsiveness of
               live view browser
 
@@ -549,8 +549,8 @@ async def create(
               image defaults apply (1920x1080@25). Only specific viewport configurations are
               supported. The server will reject unsupported combinations. Supported
               resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25,
-              1024x768@60, 1200x800@60 If refresh_rate is not provided, it will be
-              automatically determined from the width and height if they match a supported
+              1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
+              be automatically determined from the width and height if they match a supported
               configuration exactly. Note: Higher resolutions may affect the responsiveness of
               live view browser
 
@@ -681,8 +681,8 @@ async def update(
               image defaults apply (1920x1080@25). Only specific viewport configurations are
               supported. The server will reject unsupported combinations. Supported
               resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25,
-              1024x768@60, 1200x800@60 If refresh_rate is not provided, it will be
-              automatically determined from the width and height if they match a supported
+              1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
+              be automatically determined from the width and height if they match a supported
               configuration exactly. Note: Higher resolutions may affect the responsiveness of
               live view browser
 
diff --git a/src/kernel/resources/browsers/browsers.py b/src/kernel/resources/browsers/browsers.py
index 534ae062..4b61d8d8 100644
--- a/src/kernel/resources/browsers/browsers.py
+++ b/src/kernel/resources/browsers/browsers.py
@@ -188,8 +188,8 @@ def create(
               image defaults apply (1920x1080@25). Only specific viewport configurations are
               supported. The server will reject unsupported combinations. Supported
               resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25,
-              1024x768@60, 1200x800@60 If refresh_rate is not provided, it will be
-              automatically determined from the width and height if they match a supported
+              1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
+              be automatically determined from the width and height if they match a supported
               configuration exactly. Note: Higher resolutions may affect the responsiveness of
               live view browser
 
@@ -599,8 +599,8 @@ async def create(
               image defaults apply (1920x1080@25). Only specific viewport configurations are
               supported. The server will reject unsupported combinations. Supported
               resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25,
-              1024x768@60, 1200x800@60 If refresh_rate is not provided, it will be
-              automatically determined from the width and height if they match a supported
+              1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
+              be automatically determined from the width and height if they match a supported
               configuration exactly. Note: Higher resolutions may affect the responsiveness of
               live view browser
 
diff --git a/src/kernel/types/browser_create_params.py b/src/kernel/types/browser_create_params.py
index 0818760c..1e93fa6d 100644
--- a/src/kernel/types/browser_create_params.py
+++ b/src/kernel/types/browser_create_params.py
@@ -72,8 +72,8 @@ class BrowserCreateParams(TypedDict, total=False):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/browser_create_response.py b/src/kernel/types/browser_create_response.py
index efff854f..b6c28acf 100644
--- a/src/kernel/types/browser_create_response.py
+++ b/src/kernel/types/browser_create_response.py
@@ -57,8 +57,8 @@ class BrowserCreateResponse(BaseModel):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/browser_list_response.py b/src/kernel/types/browser_list_response.py
index 3ce26488..d99546d5 100644
--- a/src/kernel/types/browser_list_response.py
+++ b/src/kernel/types/browser_list_response.py
@@ -57,8 +57,8 @@ class BrowserListResponse(BaseModel):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/browser_pool.py b/src/kernel/types/browser_pool.py
index b9142f7c..fbbf2cb6 100644
--- a/src/kernel/types/browser_pool.py
+++ b/src/kernel/types/browser_pool.py
@@ -73,10 +73,10 @@ class BrowserPoolConfig(BaseModel):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
 
 
diff --git a/src/kernel/types/browser_pool_acquire_response.py b/src/kernel/types/browser_pool_acquire_response.py
index 4b70a87f..3175b398 100644
--- a/src/kernel/types/browser_pool_acquire_response.py
+++ b/src/kernel/types/browser_pool_acquire_response.py
@@ -57,8 +57,8 @@ class BrowserPoolAcquireResponse(BaseModel):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/browser_pool_create_params.py b/src/kernel/types/browser_pool_create_params.py
index afa9e6e5..81deaa68 100644
--- a/src/kernel/types/browser_pool_create_params.py
+++ b/src/kernel/types/browser_pool_create_params.py
@@ -72,8 +72,8 @@ class BrowserPoolCreateParams(TypedDict, total=False):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/browser_pool_update_params.py b/src/kernel/types/browser_pool_update_params.py
index ac23916a..63487086 100644
--- a/src/kernel/types/browser_pool_update_params.py
+++ b/src/kernel/types/browser_pool_update_params.py
@@ -78,8 +78,8 @@ class BrowserPoolUpdateParams(TypedDict, total=False):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/browser_retrieve_response.py b/src/kernel/types/browser_retrieve_response.py
index 12f58a5e..09210e8c 100644
--- a/src/kernel/types/browser_retrieve_response.py
+++ b/src/kernel/types/browser_retrieve_response.py
@@ -57,8 +57,8 @@ class BrowserRetrieveResponse(BaseModel):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/browser_update_response.py b/src/kernel/types/browser_update_response.py
index d5cb3150..01c34be5 100644
--- a/src/kernel/types/browser_update_response.py
+++ b/src/kernel/types/browser_update_response.py
@@ -57,8 +57,8 @@ class BrowserUpdateResponse(BaseModel):
     If omitted, image defaults apply (1920x1080@25). Only specific viewport
     configurations are supported. The server will reject unsupported combinations.
     Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25,
-    1440x900@25, 1024x768@60, 1200x800@60 If refresh_rate is not provided, it will
-    be automatically determined from the width and height if they match a supported
-    configuration exactly. Note: Higher resolutions may affect the responsiveness of
-    live view browser
+    1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60 If refresh_rate is not
+    provided, it will be automatically determined from the width and height if they
+    match a supported configuration exactly. Note: Higher resolutions may affect the
+    responsiveness of live view browser
     """
diff --git a/src/kernel/types/shared/browser_viewport.py b/src/kernel/types/shared/browser_viewport.py
index ab8f4273..2329dd75 100644
--- a/src/kernel/types/shared/browser_viewport.py
+++ b/src/kernel/types/shared/browser_viewport.py
@@ -12,7 +12,7 @@ class BrowserViewport(BaseModel):
 
     If omitted, image defaults apply (1920x1080@25).
     Only specific viewport configurations are supported. The server will reject unsupported combinations.
-    Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25, 1024x768@60, 1200x800@60
+    Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60
     If refresh_rate is not provided, it will be automatically determined from the width and height if they match a supported configuration exactly.
     Note: Higher resolutions may affect the responsiveness of live view browser
     """
diff --git a/src/kernel/types/shared_params/browser_viewport.py b/src/kernel/types/shared_params/browser_viewport.py
index 9236547a..7041ea55 100644
--- a/src/kernel/types/shared_params/browser_viewport.py
+++ b/src/kernel/types/shared_params/browser_viewport.py
@@ -12,7 +12,7 @@ class BrowserViewport(TypedDict, total=False):
 
     If omitted, image defaults apply (1920x1080@25).
     Only specific viewport configurations are supported. The server will reject unsupported combinations.
-    Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25, 1024x768@60, 1200x800@60
+    Supported resolutions are: 2560x1440@10, 1920x1080@25, 1920x1200@25, 1440x900@25, 1280x800@60, 1024x768@60, 1200x800@60
     If refresh_rate is not provided, it will be automatically determined from the width and height if they match a supported configuration exactly.
     Note: Higher resolutions may affect the responsiveness of live view browser
     """
diff --git a/tests/test_utils/test_json.py b/tests/test_utils/test_json.py
new file mode 100644
index 00000000..20e385b9
--- /dev/null
+++ b/tests/test_utils/test_json.py
@@ -0,0 +1,126 @@
+from __future__ import annotations
+
+import datetime
+from typing import Union
+
+import pydantic
+
+from kernel import _compat
+from kernel._utils._json import openapi_dumps
+
+
+class TestOpenapiDumps:
+    def test_basic(self) -> None:
+        data = {"key": "value", "number": 42}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"key":"value","number":42}'
+
+    def test_datetime_serialization(self) -> None:
+        dt = datetime.datetime(2023, 1, 1, 12, 0, 0)
+        data = {"datetime": dt}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"datetime":"2023-01-01T12:00:00"}'
+
+    def test_pydantic_model_serialization(self) -> None:
+        class User(pydantic.BaseModel):
+            first_name: str
+            last_name: str
+            age: int
+
+        model_instance = User(first_name="John", last_name="Kramer", age=83)
+        data = {"model": model_instance}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"first_name":"John","last_name":"Kramer","age":83}}'
+
+    def test_pydantic_model_with_default_values(self) -> None:
+        class User(pydantic.BaseModel):
+            name: str
+            role: str = "user"
+            active: bool = True
+            score: int = 0
+
+        model_instance = User(name="Alice")
+        data = {"model": model_instance}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"name":"Alice"}}'
+
+    def test_pydantic_model_with_default_values_overridden(self) -> None:
+        class User(pydantic.BaseModel):
+            name: str
+            role: str = "user"
+            active: bool = True
+
+        model_instance = User(name="Bob", role="admin", active=False)
+        data = {"model": model_instance}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"name":"Bob","role":"admin","active":false}}'
+
+    def test_pydantic_model_with_alias(self) -> None:
+        class User(pydantic.BaseModel):
+            first_name: str = pydantic.Field(alias="firstName")
+            last_name: str = pydantic.Field(alias="lastName")
+
+        model_instance = User(firstName="John", lastName="Doe")
+        data = {"model": model_instance}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"firstName":"John","lastName":"Doe"}}'
+
+    def test_pydantic_model_with_alias_and_default(self) -> None:
+        class User(pydantic.BaseModel):
+            user_name: str = pydantic.Field(alias="userName")
+            user_role: str = pydantic.Field(default="member", alias="userRole")
+            is_active: bool = pydantic.Field(default=True, alias="isActive")
+
+        model_instance = User(userName="charlie")
+        data = {"model": model_instance}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"userName":"charlie"}}'
+
+        model_with_overrides = User(userName="diana", userRole="admin", isActive=False)
+        data = {"model": model_with_overrides}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"userName":"diana","userRole":"admin","isActive":false}}'
+
+    def test_pydantic_model_with_nested_models_and_defaults(self) -> None:
+        class Address(pydantic.BaseModel):
+            street: str
+            city: str = "Unknown"
+
+        class User(pydantic.BaseModel):
+            name: str
+            address: Address
+            verified: bool = False
+
+        if _compat.PYDANTIC_V1:
+            # to handle forward references in Pydantic v1
+            User.update_forward_refs(**locals())  # type: ignore[reportDeprecated]
+
+        address = Address(street="123 Main St")
+        user = User(name="Diana", address=address)
+        data = {"user": user}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"user":{"name":"Diana","address":{"street":"123 Main St"}}}'
+
+        address_with_city = Address(street="456 Oak Ave", city="Boston")
+        user_verified = User(name="Eve", address=address_with_city, verified=True)
+        data = {"user": user_verified}
+        json_bytes = openapi_dumps(data)
+        assert (
+            json_bytes == b'{"user":{"name":"Eve","address":{"street":"456 Oak Ave","city":"Boston"},"verified":true}}'
+        )
+
+    def test_pydantic_model_with_optional_fields(self) -> None:
+        class User(pydantic.BaseModel):
+            name: str
+            email: Union[str, None]
+            phone: Union[str, None]
+
+        model_with_none = User(name="Eve", email=None, phone=None)
+        data = {"model": model_with_none}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"name":"Eve","email":null,"phone":null}}'
+
+        model_with_values = User(name="Frank", email="frank@example.com", phone=None)
+        data = {"model": model_with_values}
+        json_bytes = openapi_dumps(data)
+        assert json_bytes == b'{"model":{"name":"Frank","email":"frank@example.com","phone":null}}'