ADK agent on Agent Engine with VertexAI models result in Model not Found

[martijnschouwe]

Describe the bug
When using a model from Vertex AI the results is model not found on Agent Engine
Locally the agent works running adk web
Deploy with adk deploy

To Reproduce

The agent code
from dotenv import load_dotenv
from google.adk.agents import LlmAgent
from google.adk.models.anthropic_llm import Claude # Import needed for registration
from google.adk.models.registry import LLMRegistry # Import needed for registration
from google.genai import types
from vertexai import agent_engines
from prompt import COPY_WRITER
import os
from google.adk.models.lite_llm import LiteLlm

load_dotenv()

LLMRegistry.register(Claude)

root_agent = LlmAgent(
# The ADK's Claude class recognizes this "claude-..." prefix.
model="claude-3-7-sonnet@20250219",
name="cotton_copywriter",
instruction=COPY_WRITER,
description="You are a copy writer agent helping the marketing department",
generate_content_config=types.GenerateContentConfig(max_output_tokens=4096),
)

app = agent_engines.AdkApp(
agent=root_agent,
enable_tracing=True,
)

The deploy script:
import vertexai
from agent import root_agent
from vertexai import agent_engines
from vertexai import agent_engines
from vertexai.preview.reasoning_engines import AdkApp

vertexai.init(staging_bucket="gs://bucket", location="europe-west1")

app = AdkApp(agent=root_agent, enable_tracing=True)

remote_app = agent_engines.create(
app,
display_name="The Copywriter",
description="A Helpful Copywriter",
requirements=[
"google-adk",
"google-cloud-aiplatform[adk,agent_engines]==1.95.1",
"python-dotenv",
"cloudpickle",
"pydantic",
],
)

The Cloud trace logs:

exception.escaped	False
exception.message	Model claude-3-7-sonnet@20250219 not found.
exception.stacktrace	Traceback (most recent call last): File "/home/appuser/.cache/pypoetry/virtualenvs/reasoning-engine-assembly-service-MATOk_fk-py3.11/lib/python3.11/site-packages/opentelemetry/trace/init.py", line 589, in use_span yield span File "/home/appuser

Expected behavior
A text response just like with Gemini models, when replacing the Anthropic models with gemini the Agent Engine gives response

Desktop (please complete the following information):

• OS:MacOs
• Python version(python -V): 3.11.13
• ADK version(pip show google-adk): 1.8.0

Model Information:

• Are you using LiteLLM: No
• Which model is being used(e.g. gemini-2.5-pro) Claude sonnet 3 or 4 on VertexAI

Additional context
Also tried with a full url as described here:
https://google.github.io/adk-docs/agents/models/#model-garden-deployments

And with
https://google.github.io/adk-docs/agents/models/#fine-tuned-model-endpoints

[surajksharma07]

@martijnschouwe The issue is that Claude's model registration doesn't transfer to Agent Engine since the registry is global state that isn't serialized. As a quick workaround, wrap your AdkApp in a custom class that calls LLMRegistry.register(Claude) in __init__ before calling super().
Thanks!