You are supposed to use langchain_mcp_adapters.client.MultiServerMCPClient:

from asyncio import new_event_loop # for turning async code into sync one
from langchain_mcp_adapters.client import MultiServerMCPClient

class MyAgent:
    
    def __init__(self):
        self.event_loop = new_event_loop()

        client = MultiServerMCPClient({
            "my_service": {
                "transport":"streamable_http",
                "url":"http://localhost:3000/mcp"
            },
            # other services ...
        })

        self.agent = create_react_agent(
            model=...,
            system_prompt=...,
            tools=self.event_loop.run_until_complete(client.get_tools()) = [],
            checkpointer=...
        )

This keeps a persistent reference to the resources and will open a new connection for each tool call.