diff --git a/chatlas/_provider_openai.py b/chatlas/_provider_openai.py
index 255aa6bd..d7cefec9 100644
--- a/chatlas/_provider_openai.py
+++ b/chatlas/_provider_openai.py
@@ -49,6 +49,9 @@ def ChatOpenAI(
     model: "Optional[ResponsesModel | str]" = None,
     api_key: Optional[str] = None,
     base_url: str = "https://api.openai.com/v1",
+    service_tier: Optional[
+        Literal["auto", "default", "flex", "scale", "priority"]
+    ] = None,
     kwargs: Optional["ChatClientArgs"] = None,
 ) -> Chat["SubmitInputArgs", Response]:
     """
@@ -93,6 +96,13 @@ def ChatOpenAI(
         variable.
     base_url
         The base URL to the endpoint; the default uses OpenAI.
+    service_tier
+        Request a specific service tier. Options:
+        - `"auto"` (default): uses the service tier configured in Project settings.
+        - `"default"`: standard pricing and performance.
+        - `"flex"`: slower and cheaper.
+        - `"scale"`: batch-like pricing for high-volume use.
+        - `"priority"`: faster and more expensive.
     kwargs
         Additional arguments to pass to the `openai.OpenAI()` client
         constructor.
@@ -146,6 +156,10 @@ def ChatOpenAI(
     if model is None:
         model = log_model_default("gpt-4.1")
 
+    kwargs_chat: "SubmitInputArgs" = {}
+    if service_tier is not None:
+        kwargs_chat["service_tier"] = service_tier
+
     return Chat(
         provider=OpenAIProvider(
             api_key=api_key,
@@ -154,6 +168,7 @@ def ChatOpenAI(
             kwargs=kwargs,
         ),
         system_prompt=system_prompt,
+        kwargs_chat=kwargs_chat,
     )
 
 
@@ -260,6 +275,16 @@ def stream_text(self, chunk):
     def stream_merge_chunks(self, completion, chunk):
         if chunk.type == "response.completed":
             return chunk.response
+        elif chunk.type == "response.failed":
+            error = chunk.response.error
+            if error is None:
+                msg = "Request failed with an unknown error."
+            else:
+                msg = f"Request failed ({error.code}): {error.message}"
+            raise RuntimeError(msg)
+        elif chunk.type == "error":
+            raise RuntimeError(f"Request errored: {chunk.message}")
+
         # Since this value won't actually be used, we can lie about the type
         return cast(Response, None)
 
diff --git a/chatlas/_provider_openai_azure.py b/chatlas/_provider_openai_azure.py
index 7a1b78bc..0f2bc39d 100644
--- a/chatlas/_provider_openai_azure.py
+++ b/chatlas/_provider_openai_azure.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, Literal, Optional
 
 from openai import AsyncAzureOpenAI, AzureOpenAI
 from openai.types.chat import ChatCompletion
@@ -21,6 +21,9 @@ def ChatAzureOpenAI(
     api_version: str,
     api_key: Optional[str] = None,
     system_prompt: Optional[str] = None,
+    service_tier: Optional[
+        Literal["auto", "default", "flex", "scale", "priority"]
+    ] = None,
     kwargs: Optional["ChatAzureClientArgs"] = None,
 ) -> Chat["SubmitInputArgs", ChatCompletion]:
     """
@@ -62,6 +65,13 @@ def ChatAzureOpenAI(
         variable.
     system_prompt
         A system prompt to set the behavior of the assistant.
+    service_tier
+        Request a specific service tier. Options:
+        - `"auto"` (default): uses the service tier configured in Project settings.
+        - `"default"`: standard pricing and performance.
+        - `"flex"`: slower and cheaper.
+        - `"scale"`: batch-like pricing for high-volume use.
+        - `"priority"`: faster and more expensive.
     kwargs
         Additional arguments to pass to the `openai.AzureOpenAI()` client constructor.
 
@@ -71,6 +81,10 @@ def ChatAzureOpenAI(
         A Chat object.
     """
 
+    kwargs_chat: "SubmitInputArgs" = {}
+    if service_tier is not None:
+        kwargs_chat["service_tier"] = service_tier
+
     return Chat(
         provider=OpenAIAzureProvider(
             endpoint=endpoint,
@@ -80,6 +94,7 @@ def ChatAzureOpenAI(
             kwargs=kwargs,
         ),
         system_prompt=system_prompt,
+        kwargs_chat=kwargs_chat,
     )
 
 
diff --git a/tests/test_provider_openai.py b/tests/test_provider_openai.py
index a36e14dc..93908e93 100644
--- a/tests/test_provider_openai.py
+++ b/tests/test_provider_openai.py
@@ -105,3 +105,8 @@ def test_openai_custom_http_client():
 
 def test_openai_list_models():
     assert_list_models(ChatOpenAI)
+
+
+def test_openai_service_tier():
+    chat = ChatOpenAI(service_tier="flex")
+    assert chat.kwargs_chat.get("service_tier") == "flex"
\ No newline at end of file