From 697be58b780d380a3377f32a8aa5c4447f7f1066 Mon Sep 17 00:00:00 2001
From: cthomas <caren@letta.com>
Date: Fri, 29 Aug 2025 15:22:34 -0700
Subject: [PATCH] feat: make new message create type field optional [LET-4116]
 (#4319)

feat: make new message create type field optional
---
 letta/schemas/letta_request.py | 13 ++++++++++---
 letta/schemas/message.py       | 25 ++++---------------------
 letta/server/rest_api/app.py   |  2 --
 3 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/letta/schemas/letta_request.py b/letta/schemas/letta_request.py
index f02d1635..f8d07772 100644
--- a/letta/schemas/letta_request.py
+++ b/letta/schemas/letta_request.py
@@ -39,11 +39,18 @@ class LettaRequest(BaseModel):
     @field_validator("messages", mode="before")
     @classmethod
     def add_default_type_to_messages(cls, v):
-        """Add default 'message' type for backwards compatibility with older versions of SDK clients that don't send it"""
+        """Handle union without discriminator - default to 'message' type if not specified"""
         if isinstance(v, list):
             for item in v:
-                if isinstance(item, dict) and "type" not in item:
-                    item["type"] = "message"
+                if isinstance(item, dict):
+                    # If type is not present, determine based on fields
+                    if "type" not in item:
+                        # If it has approval-specific fields, it's an approval
+                        if "approval_request_id" in item or "approve" in item:
+                            item["type"] = "approval"
+                        else:
+                            # Default to message
+                            item["type"] = "message"
         return v
 
 
diff --git a/letta/schemas/message.py b/letta/schemas/message.py
index badd095a..41c692c5 100644
--- a/letta/schemas/message.py
+++ b/letta/schemas/message.py
@@ -78,7 +78,9 @@ class MessageCreateBase(BaseModel):
 class MessageCreate(MessageCreateBase):
     """Request to create a message"""
 
-    type: Literal[MessageCreateType.message] = Field(default=MessageCreateType.message, description="The message type to be created.")
+    type: Optional[Literal[MessageCreateType.message]] = Field(
+        default=MessageCreateType.message, description="The message type to be created."
+    )
     # In the simplified format, only allow simple roles
     role: Literal[
         MessageRole.user,
@@ -113,26 +115,7 @@ class ApprovalCreate(MessageCreateBase):
     reason: Optional[str] = Field(None, description="An optional explanation for the provided approval status")
 
 
-MessageCreateUnion = Annotated[
-    Union[MessageCreate, ApprovalCreate],
-    Field(discriminator="type"),
-]
-
-
-def create_message_create_union_schema():
-    return {
-        "oneOf": [
-            {"$ref": "#/components/schemas/MessageCreate"},
-            {"$ref": "#/components/schemas/ApprovalCreate"},
-        ],
-        "discriminator": {
-            "propertyName": "type",
-            "mapping": {
-                "message": "#/components/schemas/MessageCreate",
-                "approval": "#/components/schemas/ApprovalCreate",
-            },
-        },
-    }
+MessageCreateUnion = Union[MessageCreate, ApprovalCreate]
 
 
 class MessageUpdate(BaseModel):
diff --git a/letta/server/rest_api/app.py b/letta/server/rest_api/app.py
index dcdddd20..853b8096 100644
--- a/letta/server/rest_api/app.py
+++ b/letta/server/rest_api/app.py
@@ -29,7 +29,6 @@ from letta.schemas.letta_message_content import (
     create_letta_user_message_content_union_schema,
 )
 from letta.schemas.letta_ping import create_letta_ping_schema
-from letta.schemas.message import create_message_create_union_schema
 from letta.server.constants import REST_DEFAULT_PORT
 from letta.server.db import db_registry
 
@@ -66,7 +65,6 @@ def generate_openapi_schema(app: FastAPI):
     letta_docs["paths"] = {k: v for k, v in letta_docs["paths"].items() if not k.startswith("/openai")}
     letta_docs["info"]["title"] = "Letta API"
     letta_docs["components"]["schemas"]["LettaMessageUnion"] = create_letta_message_union_schema()
-    letta_docs["components"]["schemas"]["MessageCreateUnion"] = create_message_create_union_schema()
     letta_docs["components"]["schemas"]["LettaMessageContentUnion"] = create_letta_message_content_union_schema()
     letta_docs["components"]["schemas"]["LettaAssistantMessageContentUnion"] = create_letta_assistant_message_content_union_schema()
     letta_docs["components"]["schemas"]["LettaUserMessageContentUnion"] = create_letta_user_message_content_union_schema()