From 562beaba05e64ed341ecae767a5b14c9db49cb59 Mon Sep 17 00:00:00 2001
From: "Claud X." <1960626+claud42@users.noreply.github.com>
Date: Thu, 18 Jun 2026 14:15:33 -0700
Subject: [PATCH] fix(models): exclude LiteLlm's llm_client from field
 serialization
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Fixes #6164

LiteLlm stores its client as a Pydantic field which has no JSON serializer. Any JSON dump of a LiteLlm therefore raises `PydanticSerializationError`, which surfaces as a 500 in `adk web` / `adk api_server` whenever a LiteLlm reaches a response payload.

Ether provider (Gemini, Anthropic, Apigee) keeps its client off the model as a @cached_property, so it is never serialized. LiteLlm intentionally exposes llm_client as an injectable field for testing, so rather than convert it, mark it `exclude=True` — the client is dropped from serialization while remaining constructible and unchanged at runtime.

Testing:
  - pytest tests/unittests/models/test_litellm.py (all pass)
---
 src/google/adk/models/lite_llm.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/google/adk/models/lite_llm.py b/src/google/adk/models/lite_llm.py
index a33bce272b..bf59a1e418 100644
--- a/src/google/adk/models/lite_llm.py
+++ b/src/google/adk/models/lite_llm.py
@@ -2322,7 +2322,7 @@ class LiteLlm(BaseLlm):
     llm_client: The LLM client to use for the model.
   """
 
-  llm_client: LiteLLMClient = Field(default_factory=LiteLLMClient)
+  llm_client: LiteLLMClient = Field(default_factory=LiteLLMClient, exclude=True)
   """The LLM client to use for the model."""
 
   _additional_args: Dict[str, Any] = None