diff --git a/src/plyngent/lmproto/deepseek/openai_compat/model.py b/src/plyngent/lmproto/deepseek/openai_compat/model.py
index e7e87d1..29e53d6 100644
--- a/src/plyngent/lmproto/deepseek/openai_compat/model.py
+++ b/src/plyngent/lmproto/deepseek/openai_compat/model.py
@@ -4,25 +4,21 @@ from msgspec import UNSET, Struct
 
 from plyngent.typedef import Unset  # noqa: TC001
 
-from ...openai_compatible.model import AssistantChatMessage as BaseAssistantChatMessage
 from ...openai_compatible.model import (
-    ChatMessage,
+    AnyResponseFormat,
     ReasoningEffort,
-    ResponseFormat,
     StreamOptions,
+    SystemChatMessage,
     ToolChoiceMode,
     ToolFunctionItem,
+    UserChatMessage,
 )
+from ...openai_compatible.model import AssistantChatMessage as BaseAssistantChatMessage
 from ...openai_compatible.model import ToolChatMessage as BaseToolChatMessage
 
 type DeepSeekReasoningEffort = ReasoningEffort | Literal["max"]
 
 
-class NamedChatMessage(ChatMessage):
-    role: Literal["system", "user"]
-    name: str | Unset = UNSET
-
-
 class AssistantChatMessage(BaseAssistantChatMessage):
     prefix: bool | Unset = UNSET
     reasoning_content: str | Unset = UNSET
@@ -32,7 +28,8 @@ class ToolChatMessage(BaseToolChatMessage):
     pass
 
 
-type AnyChatMessage = NamedChatMessage | AssistantChatMessage | ToolChatMessage
+type NamedChatMessage = SystemChatMessage | UserChatMessage
+type AnyChatMessage = SystemChatMessage | UserChatMessage | AssistantChatMessage | ToolChatMessage
 
 
 class ThinkingOptions(Struct):
@@ -45,7 +42,7 @@ class ChatCompletionsParam(Struct):
     thinking: ThinkingOptions | Unset = UNSET
     reasoning_effort: DeepSeekReasoningEffort | Unset = UNSET
     max_tokens: int | Unset = UNSET
-    response_format: ResponseFormat | Unset = UNSET
+    response_format: AnyResponseFormat | Unset = UNSET
     stop: str | list[str] | Unset = UNSET
     stream: bool | Unset = UNSET
     stream_options: StreamOptions | Unset = UNSET
diff --git a/src/plyngent/lmproto/openai_compatible/__init__.py b/src/plyngent/lmproto/openai_compatible/__init__.py
index e4d5723..43aa4ed 100644
--- a/src/plyngent/lmproto/openai_compatible/__init__.py
+++ b/src/plyngent/lmproto/openai_compatible/__init__.py
@@ -16,8 +16,10 @@ from .model import ChatCompletionsParam as ChatCompletionsParam
 from .model import ChatMessage as ChatMessage
 from .model import ChunkChoice as ChunkChoice
 from .model import DeltaMessage as DeltaMessage
+from .model import DeveloperChatMessage as DeveloperChatMessage
 from .model import FinishReason as FinishReason
 from .model import GrammarSyntax as GrammarSyntax
+from .model import JsonObjectResponseFormat as JsonObjectResponseFormat
 from .model import Modality as Modality
 from .model import NamedChatMessage as NamedChatMessage
 from .model import NamedRole as NamedRole
@@ -28,8 +30,11 @@ from .model import RoleTool as RoleTool
 from .model import SchemaResponseFormat as SchemaResponseFormat
 from .model import ServiceTier as ServiceTier
 from .model import StreamOptions as StreamOptions
+from .model import SystemChatMessage as SystemChatMessage
+from .model import TextResponseFormat as TextResponseFormat
 from .model import ToolChatMessage as ToolChatMessage
 from .model import ToolChoiceMode as ToolChoiceMode
 from .model import ToolFunctionItem as ToolFunctionItem
+from .model import UserChatMessage as UserChatMessage
 from .model import Verbosity as Verbosity
 from .model import VoiceName as VoiceName
diff --git a/src/plyngent/lmproto/openai_compatible/model.py b/src/plyngent/lmproto/openai_compatible/model.py
index c3e77cd..8438eba 100644
--- a/src/plyngent/lmproto/openai_compatible/model.py
+++ b/src/plyngent/lmproto/openai_compatible/model.py
@@ -23,11 +23,21 @@ class ChatMessage(Struct):
     content: str
 
 
-class NamedChatMessage(ChatMessage):
-    role: NamedRole
+class SystemChatMessage(ChatMessage, tag_field="role", tag="system"):
     name: str | Unset = UNSET
 
 
+class UserChatMessage(ChatMessage, tag_field="role", tag="user"):
+    name: str | Unset = UNSET
+
+
+class DeveloperChatMessage(ChatMessage, tag_field="role", tag="developer"):
+    name: str | Unset = UNSET
+
+
+type NamedChatMessage = SystemChatMessage | UserChatMessage | DeveloperChatMessage
+
+
 class IDObject(Struct):
     id: str
 
@@ -37,9 +47,8 @@ class AssistantFunctionTool(Struct):
     arguments: str
 
 
-class AssistantFunctionToolCall(Struct):
+class AssistantFunctionToolCall(Struct, tag_field="type", tag="function"):
     id: str
-    type: Literal["function"]
     function: AssistantFunctionTool
 
 
@@ -48,41 +57,44 @@ class AssistantCustomTool(Struct):
     input: str
 
 
-class AssistantCustomToolCall(Struct):
+class AssistantCustomToolCall(Struct, tag_field="type", tag="custom"):
     id: str
-    type: Literal["custom"]
     custom: AssistantCustomTool
 
 
 type AnyAssistantToolCall = AssistantFunctionToolCall | AssistantCustomToolCall
 
 
-class AssistantChatMessage(ChatMessage):
-    role: RoleAssistant
+class AssistantChatMessage(ChatMessage, tag_field="role", tag="assistant"):
     name: str | Unset = UNSET
     audio: IDObject | Unset = UNSET
     refusal: str | Unset = UNSET
     tool_calls: list[AnyAssistantToolCall] | Unset = UNSET
 
 
-class ToolChatMessage(ChatMessage):
-    role: RoleTool
+class ToolChatMessage(ChatMessage, tag_field="role", tag="tool"):
     tool_call_id: str
 
 
-type AnyChatMessage = NamedChatMessage | AssistantChatMessage | ToolChatMessage
+type AnyChatMessage = (
+    SystemChatMessage | UserChatMessage | DeveloperChatMessage | AssistantChatMessage | ToolChatMessage
+)
 
 
-class ResponseFormat(Struct):
-    type: Literal["text", "json_object"]
+class TextResponseFormat(Struct, tag_field="type", tag="text"):
+    pass
 
 
-class SchemaResponseFormat(Struct):
-    type: Literal["json_schema"]
+class JsonObjectResponseFormat(Struct, tag_field="type", tag="json_object"):
+    pass
+
+
+class SchemaResponseFormat(Struct, tag_field="type", tag="json_schema"):
     json_schema: JSONSchema
 
 
-type AnyResponseFormat = ResponseFormat | SchemaResponseFormat
+type ResponseFormat = TextResponseFormat | JsonObjectResponseFormat
+type AnyResponseFormat = TextResponseFormat | JsonObjectResponseFormat | SchemaResponseFormat
 
 
 class ToolFunction(Struct):
@@ -92,13 +104,12 @@ class ToolFunction(Struct):
     strict: bool | Unset = UNSET
 
 
-class ToolFunctionItem(Struct):
-    type: Literal["function"]
+class ToolFunctionItem(Struct, tag_field="type", tag="function"):
     function: ToolFunction
 
 
-class TextFormat(Struct):
-    type: Literal["text"]
+class TextFormat(Struct, tag_field="type", tag="text"):
+    pass
 
 
 class GrammarDefinition(Struct):
@@ -106,8 +117,7 @@ class GrammarDefinition(Struct):
     definition: str
 
 
-class GrammarFormat(Struct):
-    type: Literal["grammar"]
+class GrammarFormat(Struct, tag_field="type", tag="grammar"):
     grammar: GrammarDefinition
 
 
@@ -117,8 +127,7 @@ class ToolCustom(Struct):
     format: TextFormat | GrammarFormat | Unset = UNSET
 
 
-class ToolCustomItem(Struct):
-    type: Literal["custom"]
+class ToolCustomItem(Struct, tag_field="type", tag="custom"):
     custom: ToolCustom
 
 
@@ -134,8 +143,7 @@ class ModerationOptions(Struct):
     model: str
 
 
-class PredictionOptions(Struct):
-    type: Literal["content"]
+class PredictionOptions(Struct, tag_field="type", tag="content"):
     content: str
 
 
@@ -149,8 +157,7 @@ class AllowedTools(Struct):
     tools: list[AnyToolItem]
 
 
-class AllowedToolChoice(Struct):
-    type: Literal["allowed_tools"]
+class AllowedToolChoice(Struct, tag_field="type", tag="allowed_tools"):
     allowed_tools: AllowedTools
 
 
diff --git a/src/plyngent/typedef.py b/src/plyngent/typedef.py
index e7709cc..b9c2c37 100644
--- a/src/plyngent/typedef.py
+++ b/src/plyngent/typedef.py
@@ -1,6 +1,7 @@
-from typing import Any, Literal
+from typing import Any
 
 from msgspec import UnsetType
 
 type JSONSchema = dict[str, Any]
-type Unset = Literal[UnsetType.UNSET]
+# Assignment (not PEP 695 `type`) so msgspec recognizes UnsetType in unions.
+Unset = UnsetType