fix: Add version compatibility checks for LiteLLM and OpenAI

pyproject.toml

@@ -44,6 +44,7 @@ dependencies = [
   "opentelemetry-api>=1.31.0, <2.0.0",              # OpenTelemetry
   "opentelemetry-exporter-gcp-trace>=1.9.0, <2.0.0",
   "opentelemetry-sdk>=1.31.0, <2.0.0",
+  "packaging>=24.0, <25.0",                         # Version parsing in runtime guards
   "pydantic>=2.0, <3.0.0",                          # For data validation/models
   "python-dateutil>=2.9.0.post0, <3.0.0",           # For Vertext AI Session Service
   "python-dotenv>=1.0.0, <2.0.0",                   # To manage environment variables
@@ -102,9 +103,9 @@ test = [
   "langchain-community>=0.3.17",
   # langgraph 0.5 removed langgraph.graph.graph which we depend on
   "langgraph>=0.2.60, <= 0.4.10",    # For LangGraphAgent
-  "litellm>=1.75.5, <2.0.0",                 # For LiteLLM tests
+  "litellm>=1.75.5, <2.0.0",         # For LiteLLM tests; upper-bounded due to OpenAI API coupling
   "llama-index-readers-file>=0.4.0", # For retrieval tests
-  "openai<=1.99.9", # For LiteLLM
+  "openai<=1.99.9",                  # For LiteLLM; upper-bound to avoid breaking changes
   "pytest-asyncio>=0.25.0",
   "pytest-mock>=3.14.0",
   "pytest-xdist>=3.6.1",
@@ -129,7 +130,8 @@ extensions = [
   "crewai[tools];python_version>='3.10'", # For CrewaiTool
   "docker>=7.0.0",                        # For ContainerCodeExecutor
   "langgraph>=0.2.60",                    # For LangGraphAgent
-  "litellm>=1.75.5",                      # For LiteLlm class. Currently has OpenAI limitations. TODO: once LiteLlm fix it
+  "litellm>=1.75.5, <2.0.0",              # For LiteLlm class. Upper-bounded due to OpenAI API coupling; TODO: relax once LiteLlm fixes it
+  "openai<=1.99.9",                       # For LiteLlm class. Upper-bound required due to LiteLlm/OpenAI breaking changes
   "llama-index-readers-file>=0.4.0",      # For retrieval using LlamaIndex.
   "lxml>=5.3.0",                          # For load_web_page tool.
   "toolbox-core>=0.1.0",                  # For tools.toolbox_toolset.ToolboxToolset

src/google/adk/models/lite_llm.py

@@ -15,6 +15,7 @@
 from __future__ import annotations
 
 import base64
+import importlib.metadata as im
 import json
 import logging
 from typing import Any
@@ -50,6 +51,7 @@
 from litellm import Message
 from litellm import ModelResponse
 from litellm import OpenAIMessageContent
+from packaging.version import Version
 from pydantic import BaseModel
 from pydantic import Field
 from typing_extensions import override
@@ -67,6 +69,37 @@
 _EXCLUDED_PART_FIELD = {"inline_data": {"data"}}
 
 
+def _assert_litellm_openai_compat() -> None:
+  """Fail fast if installed litellm/openai versions are incompatible.
+
+  Policy:
+    - litellm < 2.0.0
+    - openai <= 1.99.9
+  """
+
+  try:
+    litellm_version = im.version("litellm")
+  except Exception:
+    # If not installed, defer to import-time errors elsewhere
+    return
+
+  try:
+    openai_version = im.version("openai")
+  except Exception:
+    # If openai is not installed but user still tries to use LiteLLM with providers
+    # that require it, they will hit an import/runtime error later. No-op here.
+    return
+
+  if Version(litellm_version) >= Version("2.0.0"):
+    raise RuntimeError(
+        f"Unsupported litellm {litellm_version}; require < 2.0.0"
+    )
+  if Version(openai_version) > Version("1.99.9"):
+    raise RuntimeError(
+        f"Unsupported openai {openai_version}; require <= 1.99.9"
+    )
+
+
 class FunctionChunk(BaseModel):
   id: Optional[str]
   name: Optional[str]
@@ -704,6 +737,7 @@ def __init__(self, model: str, **kwargs):
       **kwargs: Additional arguments to pass to the litellm completion api.
     """
     super().__init__(model=model, **kwargs)
+    _assert_litellm_openai_compat()
     self._additional_args = kwargs
     # preventing generation call with llm_client
     # and overriding messages, tools and stream which are managed internally