diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index fb1bd8f489..6a197bef5a 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "1.16.2"
+  ".": "1.17.0"
 }
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3b22f06aae..0da030b337 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,15 @@
 # Changelog
 
+## 1.17.0 (2024-04-10)
+
+Full Changelog: [v1.16.2...v1.17.0](https://github.com/openai/openai-python/compare/v1.16.2...v1.17.0)
+
+### Features
+
+* **api:** add additional messages when creating thread run ([#1298](https://github.com/openai/openai-python/issues/1298)) ([70eb081](https://github.com/openai/openai-python/commit/70eb081804b14cc8c151ebd85458545a50a074fd))
+* **client:** add DefaultHttpxClient and DefaultAsyncHttpxClient ([#1302](https://github.com/openai/openai-python/issues/1302)) ([69cdfc3](https://github.com/openai/openai-python/commit/69cdfc319fff7ebf28cdd13cc6c1761b7d97811d))
+* **models:** add to_dict & to_json helper methods ([#1305](https://github.com/openai/openai-python/issues/1305)) ([40a881d](https://github.com/openai/openai-python/commit/40a881d10442af8b445ce030f8ab338710e1c4c8))
+
 ## 1.16.2 (2024-04-04)
 
 Full Changelog: [v1.16.1...v1.16.2](https://github.com/openai/openai-python/compare/v1.16.1...v1.16.2)
diff --git a/README.md b/README.md
index 5264026dc9..3bdd6c4a43 100644
--- a/README.md
+++ b/README.md
@@ -200,10 +200,10 @@ We recommend that you always instantiate a client (e.g., with `client = OpenAI()
 
 ## Using types
 
-Nested request parameters are [TypedDicts](https://docs.python.org/3/library/typing.html#typing.TypedDict). Responses are [Pydantic models](https://docs.pydantic.dev), which provide helper methods for things like:
+Nested request parameters are [TypedDicts](https://docs.python.org/3/library/typing.html#typing.TypedDict). Responses are [Pydantic models](https://docs.pydantic.dev) which also provide helper methods for things like:
 
-- Serializing back into JSON, `model.model_dump_json(indent=2, exclude_unset=True)`
-- Converting to a dictionary, `model.model_dump(exclude_unset=True)`
+- Serializing back into JSON, `model.to_json()`
+- Converting to a dictionary, `model.to_dict()`
 
 Typed requests and responses provide autocomplete and documentation within your editor. If you would like to see type errors in VS Code to help catch bugs earlier, set `python.analysis.typeCheckingMode` to `basic`.
 
@@ -549,13 +549,12 @@ You can directly override the [httpx client](https://www.python-httpx.org/api/#c
 - Additional [advanced](https://www.python-httpx.org/advanced/#client-instances) functionality
 
 ```python
-import httpx
-from openai import OpenAI
+from openai import OpenAI, DefaultHttpxClient
 
 client = OpenAI(
     # Or use the `OPENAI_BASE_URL` env var
     base_url="http://my.test.server.example.com:8083",
-    http_client=httpx.Client(
+    http_client=DefaultHttpxClient(
         proxies="http://my.test.proxy.example.com",
         transport=httpx.HTTPTransport(local_address="0.0.0.0"),
     ),
@@ -595,7 +594,7 @@ completion = client.chat.completions.create(
         },
     ],
 )
-print(completion.model_dump_json(indent=2))
+print(completion.to_json())
 ```
 
 In addition to the options provided in the base `OpenAI` client, the following options are provided:
diff --git a/examples/azure.py b/examples/azure.py
index a28b8cc433..6936c4cb0e 100755
--- a/examples/azure.py
+++ b/examples/azure.py
@@ -20,7 +20,7 @@
         },
     ],
 )
-print(completion.model_dump_json(indent=2))
+print(completion.to_json())
 
 
 deployment_client = AzureOpenAI(
@@ -40,4 +40,4 @@
         },
     ],
 )
-print(completion.model_dump_json(indent=2))
+print(completion.to_json())
diff --git a/examples/azure_ad.py b/examples/azure_ad.py
index f13079dd04..1b0d81863d 100755
--- a/examples/azure_ad.py
+++ b/examples/azure_ad.py
@@ -27,4 +27,4 @@
         },
     ],
 )
-print(completion.model_dump_json(indent=2))
+print(completion.to_json())
diff --git a/examples/streaming.py b/examples/streaming.py
index 368fa5f911..9a84891a83 100755
--- a/examples/streaming.py
+++ b/examples/streaming.py
@@ -22,12 +22,12 @@ def sync_main() -> None:
 
     # You can manually control iteration over the response
     first = next(response)
-    print(f"got response data: {first.model_dump_json(indent=2)}")
+    print(f"got response data: {first.to_json()}")
 
     # Or you could automatically iterate through all of data.
     # Note that the for loop will not exit until *all* of the data has been processed.
     for data in response:
-        print(data.model_dump_json())
+        print(data.to_json())
 
 
 async def async_main() -> None:
@@ -43,12 +43,12 @@ async def async_main() -> None:
     # You can manually control iteration over the response.
     # In Python 3.10+ you can also use the `await anext(response)` builtin instead
     first = await response.__anext__()
-    print(f"got response data: {first.model_dump_json(indent=2)}")
+    print(f"got response data: {first.to_json()}")
 
     # Or you could automatically iterate through all of data.
     # Note that the for loop will not exit until *all* of the data has been processed.
     async for data in response:
-        print(data.model_dump_json())
+        print(data.to_json())
 
 
 sync_main()
diff --git a/pyproject.toml b/pyproject.toml
index 67006726fb..b3043bc0cd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "openai"
-version = "1.16.2"
+version = "1.17.0"
 description = "The official Python library for the openai API"
 dynamic = ["readme"]
 license = "Apache-2.0"
diff --git a/src/openai/__init__.py b/src/openai/__init__.py
index cd05a749da..1daa26f7b7 100644
--- a/src/openai/__init__.py
+++ b/src/openai/__init__.py
@@ -29,6 +29,7 @@
     UnprocessableEntityError,
     APIResponseValidationError,
 )
+from ._base_client import DefaultHttpxClient, DefaultAsyncHttpxClient
 from ._utils._logs import setup_logging as _setup_logging
 
 __all__ = [
@@ -67,6 +68,8 @@
     "DEFAULT_TIMEOUT",
     "DEFAULT_MAX_RETRIES",
     "DEFAULT_CONNECTION_LIMITS",
+    "DefaultHttpxClient",
+    "DefaultAsyncHttpxClient",
 ]
 
 from .lib import azure as _azure
diff --git a/src/openai/_base_client.py b/src/openai/_base_client.py
index 502ed7c7ae..0bb284a211 100644
--- a/src/openai/_base_client.py
+++ b/src/openai/_base_client.py
@@ -716,7 +716,27 @@ def _idempotency_key(self) -> str:
         return f"stainless-python-retry-{uuid.uuid4()}"
 
 
-class SyncHttpxClientWrapper(httpx.Client):
+class _DefaultHttpxClient(httpx.Client):
+    def __init__(self, **kwargs: Any) -> None:
+        kwargs.setdefault("timeout", DEFAULT_TIMEOUT)
+        kwargs.setdefault("limits", DEFAULT_CONNECTION_LIMITS)
+        kwargs.setdefault("follow_redirects", True)
+        super().__init__(**kwargs)
+
+
+if TYPE_CHECKING:
+    DefaultHttpxClient = httpx.Client
+    """An alias to `httpx.Client` that provides the same defaults that this SDK
+    uses internally.
+
+    This is useful because overriding the `http_client` with your own instance of
+    `httpx.Client` will result in httpx's defaults being used, not ours.
+    """
+else:
+    DefaultHttpxClient = _DefaultHttpxClient
+
+
+class SyncHttpxClientWrapper(DefaultHttpxClient):
     def __del__(self) -> None:
         try:
             self.close()
@@ -1262,7 +1282,27 @@ def get_api_list(
         return self._request_api_list(model, page, opts)
 
 
-class AsyncHttpxClientWrapper(httpx.AsyncClient):
+class _DefaultAsyncHttpxClient(httpx.AsyncClient):
+    def __init__(self, **kwargs: Any) -> None:
+        kwargs.setdefault("timeout", DEFAULT_TIMEOUT)
+        kwargs.setdefault("limits", DEFAULT_CONNECTION_LIMITS)
+        kwargs.setdefault("follow_redirects", True)
+        super().__init__(**kwargs)
+
+
+if TYPE_CHECKING:
+    DefaultAsyncHttpxClient = httpx.AsyncClient
+    """An alias to `httpx.AsyncClient` that provides the same defaults that this SDK
+    uses internally.
+
+    This is useful because overriding the `http_client` with your own instance of
+    `httpx.AsyncClient` will result in httpx's defaults being used, not ours.
+    """
+else:
+    DefaultAsyncHttpxClient = _DefaultAsyncHttpxClient
+
+
+class AsyncHttpxClientWrapper(DefaultAsyncHttpxClient):
     def __del__(self) -> None:
         try:
             # TODO(someday): support non asyncio runtimes here
diff --git a/src/openai/_client.py b/src/openai/_client.py
index 7fe2c9af79..e9169df72a 100644
--- a/src/openai/_client.py
+++ b/src/openai/_client.py
@@ -74,7 +74,9 @@ def __init__(
         max_retries: int = DEFAULT_MAX_RETRIES,
         default_headers: Mapping[str, str] | None = None,
         default_query: Mapping[str, object] | None = None,
-        # Configure a custom httpx client. See the [httpx documentation](https://www.python-httpx.org/api/#client) for more details.
+        # Configure a custom httpx client.
+        # We provide a `DefaultHttpxClient` class that you can pass to retain the default values we use for `limits`, `timeout` & `follow_redirects`.
+        # See the [httpx documentation](https://www.python-httpx.org/api/#client) for more details.
         http_client: httpx.Client | None = None,
         # Enable or disable schema validation for data returned by the API.
         # When enabled an error APIResponseValidationError is raised
@@ -272,7 +274,9 @@ def __init__(
         max_retries: int = DEFAULT_MAX_RETRIES,
         default_headers: Mapping[str, str] | None = None,
         default_query: Mapping[str, object] | None = None,
-        # Configure a custom httpx client. See the [httpx documentation](https://www.python-httpx.org/api/#asyncclient) for more details.
+        # Configure a custom httpx client.
+        # We provide a `DefaultAsyncHttpxClient` class that you can pass to retain the default values we use for `limits`, `timeout` & `follow_redirects`.
+        # See the [httpx documentation](https://www.python-httpx.org/api/#asyncclient) for more details.
         http_client: httpx.AsyncClient | None = None,
         # Enable or disable schema validation for data returned by the API.
         # When enabled an error APIResponseValidationError is raised
diff --git a/src/openai/_models.py b/src/openai/_models.py
index 0f001150f5..80ab51256f 100644
--- a/src/openai/_models.py
+++ b/src/openai/_models.py
@@ -90,6 +90,79 @@ def model_fields_set(self) -> set[str]:
         class Config(pydantic.BaseConfig):  # pyright: ignore[reportDeprecated]
             extra: Any = pydantic.Extra.allow  # type: ignore
 
+    def to_dict(
+        self,
+        *,
+        mode: Literal["json", "python"] = "python",
+        use_api_names: bool = True,
+        exclude_unset: bool = True,
+        exclude_defaults: bool = False,
+        exclude_none: bool = False,
+        warnings: bool = True,
+    ) -> dict[str, object]:
+        """Recursively generate a dictionary representation of the model, optionally specifying which fields to include or exclude.
+
+        By default, fields that were not set by the API will not be included,
+        and keys will match the API response, *not* the property names from the model.
+
+        For example, if the API responds with `"fooBar": true` but we've defined a `foo_bar: bool` property,
+        the output will use the `"fooBar"` key (unless `use_api_names=False` is passed).
+
+        Args:
+            mode:
+                If mode is 'json', the dictionary will only contain JSON serializable types. e.g. `datetime` will be turned into a string, `"2024-3-22T18:11:19.117000Z"`.
+                If mode is 'python', the dictionary may contain any Python objects. e.g. `datetime(2024, 3, 22)`
+
+            use_api_names: Whether to use the key that the API responded with or the property name. Defaults to `True`.
+            exclude_unset: Whether to exclude fields that have not been explicitly set.
+            exclude_defaults: Whether to exclude fields that are set to their default value from the output.
+            exclude_none: Whether to exclude fields that have a value of `None` from the output.
+            warnings: Whether to log warnings when invalid fields are encountered. This is only supported in Pydantic v2.
+        """
+        return self.model_dump(
+            mode=mode,
+            by_alias=use_api_names,
+            exclude_unset=exclude_unset,
+            exclude_defaults=exclude_defaults,
+            exclude_none=exclude_none,
+            warnings=warnings,
+        )
+
+    def to_json(
+        self,
+        *,
+        indent: int | None = 2,
+        use_api_names: bool = True,
+        exclude_unset: bool = True,
+        exclude_defaults: bool = False,
+        exclude_none: bool = False,
+        warnings: bool = True,
+    ) -> str:
+        """Generates a JSON string representing this model as it would be received from or sent to the API (but with indentation).
+
+        By default, fields that were not set by the API will not be included,
+        and keys will match the API response, *not* the property names from the model.
+
+        For example, if the API responds with `"fooBar": true` but we've defined a `foo_bar: bool` property,
+        the output will use the `"fooBar"` key (unless `use_api_names=False` is passed).
+
+        Args:
+            indent: Indentation to use in the JSON output. If `None` is passed, the output will be compact. Defaults to `2`
+            use_api_names: Whether to use the key that the API responded with or the property name. Defaults to `True`.
+            exclude_unset: Whether to exclude fields that have not been explicitly set.
+            exclude_defaults: Whether to exclude fields that have the default value.
+            exclude_none: Whether to exclude fields that have a value of `None`.
+            warnings: Whether to show any warnings that occurred during serialization. This is only supported in Pydantic v2.
+        """
+        return self.model_dump_json(
+            indent=indent,
+            by_alias=use_api_names,
+            exclude_unset=exclude_unset,
+            exclude_defaults=exclude_defaults,
+            exclude_none=exclude_none,
+            warnings=warnings,
+        )
+
     @override
     def __str__(self) -> str:
         # mypy complains about an invalid self arg
diff --git a/src/openai/_version.py b/src/openai/_version.py
index 85803a60a6..0c55423216 100644
--- a/src/openai/_version.py
+++ b/src/openai/_version.py
@@ -1,4 +1,4 @@
 # File generated from our OpenAPI spec by Stainless. See CONTRIBUTING.md for details.
 
 __title__ = "openai"
-__version__ = "1.16.2"  # x-release-please-version
+__version__ = "1.17.0"  # x-release-please-version
diff --git a/src/openai/lib/_validators.py b/src/openai/lib/_validators.py
index e36f0e95fb..cf24cd2294 100644
--- a/src/openai/lib/_validators.py
+++ b/src/openai/lib/_validators.py
@@ -678,9 +678,11 @@ def write_out_file(df: pd.DataFrame, fname: str, any_remediations: bool, auto_ac
             df_train = df.sample(n=n_train, random_state=42)
             df_valid = df.drop(df_train.index)
             df_train[["prompt", "completion"]].to_json(  # type: ignore
-                fnames[0], lines=True, orient="records", force_ascii=False
+                fnames[0], lines=True, orient="records", force_ascii=False, indent=None
+            )
+            df_valid[["prompt", "completion"]].to_json(
+                fnames[1], lines=True, orient="records", force_ascii=False, indent=None
             )
-            df_valid[["prompt", "completion"]].to_json(fnames[1], lines=True, orient="records", force_ascii=False)
 
             n_classes, pos_class = get_classification_hyperparams(df)
             additional_params += " --compute_classification_metrics"
@@ -690,7 +692,9 @@ def write_out_file(df: pd.DataFrame, fname: str, any_remediations: bool, auto_ac
                 additional_params += f" --classification_n_classes {n_classes}"
         else:
             assert len(fnames) == 1
-            df[["prompt", "completion"]].to_json(fnames[0], lines=True, orient="records", force_ascii=False)
+            df[["prompt", "completion"]].to_json(
+                fnames[0], lines=True, orient="records", force_ascii=False, indent=None
+            )
 
         # Add -v VALID_FILE if we split the file into train / valid
         files_string = ("s" if split else "") + " to `" + ("` and `".join(fnames))
diff --git a/src/openai/resources/beta/threads/runs/runs.py b/src/openai/resources/beta/threads/runs/runs.py
index 4529c65025..8576a5c09a 100644
--- a/src/openai/resources/beta/threads/runs/runs.py
+++ b/src/openai/resources/beta/threads/runs/runs.py
@@ -75,6 +75,7 @@ def create(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -100,6 +101,8 @@ def create(
               is useful for modifying the behavior on a per-run basis without overriding other
               instructions.
 
+          additional_messages: Adds additional messages to the thread before creating the run.
+
           instructions: Overrides the
               [instructions](https://platform.openai.com/docs/api-reference/assistants/createAssistant)
               of the assistant. This is useful for modifying the behavior on a per-run basis.
@@ -143,6 +146,7 @@ def create(
         assistant_id: str,
         stream: Literal[True],
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -171,6 +175,8 @@ def create(
               is useful for modifying the behavior on a per-run basis without overriding other
               instructions.
 
+          additional_messages: Adds additional messages to the thread before creating the run.
+
           instructions: Overrides the
               [instructions](https://platform.openai.com/docs/api-reference/assistants/createAssistant)
               of the assistant. This is useful for modifying the behavior on a per-run basis.
@@ -210,6 +216,7 @@ def create(
         assistant_id: str,
         stream: bool,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -238,6 +245,8 @@ def create(
               is useful for modifying the behavior on a per-run basis without overriding other
               instructions.
 
+          additional_messages: Adds additional messages to the thread before creating the run.
+
           instructions: Overrides the
               [instructions](https://platform.openai.com/docs/api-reference/assistants/createAssistant)
               of the assistant. This is useful for modifying the behavior on a per-run basis.
@@ -276,6 +285,7 @@ def create(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -298,6 +308,7 @@ def create(
                 {
                     "assistant_id": assistant_id,
                     "additional_instructions": additional_instructions,
+                    "additional_messages": additional_messages,
                     "instructions": instructions,
                     "metadata": metadata,
                     "model": model,
@@ -505,6 +516,7 @@ def create_and_poll(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -528,6 +540,7 @@ def create_and_poll(
             thread_id=thread_id,
             assistant_id=assistant_id,
             additional_instructions=additional_instructions,
+            additional_messages=additional_messages,
             instructions=instructions,
             metadata=metadata,
             model=model,
@@ -557,6 +570,7 @@ def create_and_stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -580,6 +594,7 @@ def create_and_stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -603,6 +618,7 @@ def create_and_stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -634,6 +650,7 @@ def create_and_stream(
                 {
                     "assistant_id": assistant_id,
                     "additional_instructions": additional_instructions,
+                    "additional_messages": additional_messages,
                     "instructions": instructions,
                     "metadata": metadata,
                     "model": model,
@@ -703,6 +720,7 @@ def stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -725,6 +743,7 @@ def stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -747,6 +766,7 @@ def stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -778,6 +798,7 @@ def stream(
                 {
                     "assistant_id": assistant_id,
                     "additional_instructions": additional_instructions,
+                    "additional_messages": additional_messages,
                     "instructions": instructions,
                     "metadata": metadata,
                     "model": model,
@@ -1100,6 +1121,7 @@ async def create(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1125,6 +1147,8 @@ async def create(
               is useful for modifying the behavior on a per-run basis without overriding other
               instructions.
 
+          additional_messages: Adds additional messages to the thread before creating the run.
+
           instructions: Overrides the
               [instructions](https://platform.openai.com/docs/api-reference/assistants/createAssistant)
               of the assistant. This is useful for modifying the behavior on a per-run basis.
@@ -1168,6 +1192,7 @@ async def create(
         assistant_id: str,
         stream: Literal[True],
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1196,6 +1221,8 @@ async def create(
               is useful for modifying the behavior on a per-run basis without overriding other
               instructions.
 
+          additional_messages: Adds additional messages to the thread before creating the run.
+
           instructions: Overrides the
               [instructions](https://platform.openai.com/docs/api-reference/assistants/createAssistant)
               of the assistant. This is useful for modifying the behavior on a per-run basis.
@@ -1235,6 +1262,7 @@ async def create(
         assistant_id: str,
         stream: bool,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1263,6 +1291,8 @@ async def create(
               is useful for modifying the behavior on a per-run basis without overriding other
               instructions.
 
+          additional_messages: Adds additional messages to the thread before creating the run.
+
           instructions: Overrides the
               [instructions](https://platform.openai.com/docs/api-reference/assistants/createAssistant)
               of the assistant. This is useful for modifying the behavior on a per-run basis.
@@ -1301,6 +1331,7 @@ async def create(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1323,6 +1354,7 @@ async def create(
                 {
                     "assistant_id": assistant_id,
                     "additional_instructions": additional_instructions,
+                    "additional_messages": additional_messages,
                     "instructions": instructions,
                     "metadata": metadata,
                     "model": model,
@@ -1530,6 +1562,7 @@ async def create_and_poll(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1553,6 +1586,7 @@ async def create_and_poll(
             thread_id=thread_id,
             assistant_id=assistant_id,
             additional_instructions=additional_instructions,
+            additional_messages=additional_messages,
             instructions=instructions,
             metadata=metadata,
             model=model,
@@ -1582,6 +1616,7 @@ def create_and_stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1605,6 +1640,7 @@ def create_and_stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1628,6 +1664,7 @@ def create_and_stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1661,6 +1698,7 @@ def create_and_stream(
                 {
                     "assistant_id": assistant_id,
                     "additional_instructions": additional_instructions,
+                    "additional_messages": additional_messages,
                     "instructions": instructions,
                     "metadata": metadata,
                     "model": model,
@@ -1730,6 +1768,7 @@ def stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1752,6 +1791,7 @@ def stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1774,6 +1814,7 @@ def stream(
         *,
         assistant_id: str,
         additional_instructions: Optional[str] | NotGiven = NOT_GIVEN,
+        additional_messages: Optional[Iterable[run_create_params.AdditionalMessage]] | NotGiven = NOT_GIVEN,
         instructions: Optional[str] | NotGiven = NOT_GIVEN,
         metadata: Optional[object] | NotGiven = NOT_GIVEN,
         model: Optional[str] | NotGiven = NOT_GIVEN,
@@ -1807,6 +1848,7 @@ def stream(
                 {
                     "assistant_id": assistant_id,
                     "additional_instructions": additional_instructions,
+                    "additional_messages": additional_messages,
                     "instructions": instructions,
                     "metadata": metadata,
                     "model": model,
diff --git a/src/openai/types/beta/threads/run_create_params.py b/src/openai/types/beta/threads/run_create_params.py
index ac185973a5..e9bc19d980 100644
--- a/src/openai/types/beta/threads/run_create_params.py
+++ b/src/openai/types/beta/threads/run_create_params.py
@@ -2,12 +2,12 @@
 
 from __future__ import annotations
 
-from typing import Union, Iterable, Optional
+from typing import List, Union, Iterable, Optional
 from typing_extensions import Literal, Required, TypedDict
 
 from ..assistant_tool_param import AssistantToolParam
 
-__all__ = ["RunCreateParamsBase", "RunCreateParamsNonStreaming", "RunCreateParamsStreaming"]
+__all__ = ["RunCreateParamsBase", "AdditionalMessage", "RunCreateParamsNonStreaming", "RunCreateParamsStreaming"]
 
 
 class RunCreateParamsBase(TypedDict, total=False):
@@ -25,6 +25,9 @@ class RunCreateParamsBase(TypedDict, total=False):
     other instructions.
     """
 
+    additional_messages: Optional[Iterable[AdditionalMessage]]
+    """Adds additional messages to the thread before creating the run."""
+
     instructions: Optional[str]
     """
     Overrides the
@@ -62,6 +65,36 @@ class RunCreateParamsBase(TypedDict, total=False):
     """
 
 
+class AdditionalMessage(TypedDict, total=False):
+    content: Required[str]
+    """The content of the message."""
+
+    role: Required[Literal["user", "assistant"]]
+    """The role of the entity that is creating the message. Allowed values include:
+
+    - `user`: Indicates the message is sent by an actual user and should be used in
+      most cases to represent user-generated messages.
+    - `assistant`: Indicates the message is generated by the assistant. Use this
+      value to insert messages from the assistant into the conversation.
+    """
+
+    file_ids: List[str]
+    """
+    A list of [File](https://platform.openai.com/docs/api-reference/files) IDs that
+    the message should use. There can be a maximum of 10 files attached to a
+    message. Useful for tools like `retrieval` and `code_interpreter` that can
+    access and use files.
+    """
+
+    metadata: Optional[object]
+    """Set of 16 key-value pairs that can be attached to an object.
+
+    This can be useful for storing additional information about the object in a
+    structured format. Keys can be a maximum of 64 characters long and values can be
+    a maxium of 512 characters long.
+    """
+
+
 class RunCreateParamsNonStreaming(RunCreateParamsBase):
     stream: Optional[Literal[False]]
     """
diff --git a/tests/api_resources/beta/threads/test_runs.py b/tests/api_resources/beta/threads/test_runs.py
index b9f392dc87..271bcccdd3 100644
--- a/tests/api_resources/beta/threads/test_runs.py
+++ b/tests/api_resources/beta/threads/test_runs.py
@@ -36,6 +36,26 @@ def test_method_create_with_all_params_overload_1(self, client: OpenAI) -> None:
             "string",
             assistant_id="string",
             additional_instructions="string",
+            additional_messages=[
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+            ],
             instructions="string",
             metadata={},
             model="string",
@@ -95,6 +115,26 @@ def test_method_create_with_all_params_overload_2(self, client: OpenAI) -> None:
             assistant_id="string",
             stream=True,
             additional_instructions="string",
+            additional_messages=[
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+            ],
             instructions="string",
             metadata={},
             model="string",
@@ -492,6 +532,26 @@ async def test_method_create_with_all_params_overload_1(self, async_client: Asyn
             "string",
             assistant_id="string",
             additional_instructions="string",
+            additional_messages=[
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+            ],
             instructions="string",
             metadata={},
             model="string",
@@ -551,6 +611,26 @@ async def test_method_create_with_all_params_overload_2(self, async_client: Asyn
             assistant_id="string",
             stream=True,
             additional_instructions="string",
+            additional_messages=[
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+                {
+                    "role": "user",
+                    "content": "x",
+                    "file_ids": ["string"],
+                    "metadata": {},
+                },
+            ],
             instructions="string",
             metadata={},
             model="string",
diff --git a/tests/test_models.py b/tests/test_models.py
index d003d32181..969e4eb315 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -501,6 +501,42 @@ class Model(BaseModel):
     assert "resource_id" in m.model_fields_set
 
 
+def test_to_dict() -> None:
+    class Model(BaseModel):
+        foo: Optional[str] = Field(alias="FOO", default=None)
+
+    m = Model(FOO="hello")
+    assert m.to_dict() == {"FOO": "hello"}
+    assert m.to_dict(use_api_names=False) == {"foo": "hello"}
+
+    m2 = Model()
+    assert m2.to_dict() == {}
+    assert m2.to_dict(exclude_unset=False) == {"FOO": None}
+    assert m2.to_dict(exclude_unset=False, exclude_none=True) == {}
+    assert m2.to_dict(exclude_unset=False, exclude_defaults=True) == {}
+
+    m3 = Model(FOO=None)
+    assert m3.to_dict() == {"FOO": None}
+    assert m3.to_dict(exclude_none=True) == {}
+    assert m3.to_dict(exclude_defaults=True) == {}
+
+    if PYDANTIC_V2:
+
+        class Model2(BaseModel):
+            created_at: datetime
+
+        time_str = "2024-03-21T11:39:01.275859"
+        m4 = Model2.construct(created_at=time_str)
+        assert m4.to_dict(mode="python") == {"created_at": datetime.fromisoformat(time_str)}
+        assert m4.to_dict(mode="json") == {"created_at": time_str}
+    else:
+        with pytest.raises(ValueError, match="mode is only supported in Pydantic v2"):
+            m.to_dict(mode="json")
+
+        with pytest.raises(ValueError, match="warnings is only supported in Pydantic v2"):
+            m.to_dict(warnings=False)
+
+
 def test_forwards_compat_model_dump_method() -> None:
     class Model(BaseModel):
         foo: Optional[str] = Field(alias="FOO", default=None)
@@ -532,6 +568,34 @@ class Model(BaseModel):
             m.model_dump(warnings=False)
 
 
+def test_to_json() -> None:
+    class Model(BaseModel):
+        foo: Optional[str] = Field(alias="FOO", default=None)
+
+    m = Model(FOO="hello")
+    assert json.loads(m.to_json()) == {"FOO": "hello"}
+    assert json.loads(m.to_json(use_api_names=False)) == {"foo": "hello"}
+
+    if PYDANTIC_V2:
+        assert m.to_json(indent=None) == '{"FOO":"hello"}'
+    else:
+        assert m.to_json(indent=None) == '{"FOO": "hello"}'
+
+    m2 = Model()
+    assert json.loads(m2.to_json()) == {}
+    assert json.loads(m2.to_json(exclude_unset=False)) == {"FOO": None}
+    assert json.loads(m2.to_json(exclude_unset=False, exclude_none=True)) == {}
+    assert json.loads(m2.to_json(exclude_unset=False, exclude_defaults=True)) == {}
+
+    m3 = Model(FOO=None)
+    assert json.loads(m3.to_json()) == {"FOO": None}
+    assert json.loads(m3.to_json(exclude_none=True)) == {}
+
+    if not PYDANTIC_V2:
+        with pytest.raises(ValueError, match="warnings is only supported in Pydantic v2"):
+            m.to_json(warnings=False)
+
+
 def test_forwards_compat_model_dump_json_method() -> None:
     class Model(BaseModel):
         foo: Optional[str] = Field(alias="FOO", default=None)