[BUG] Managed MCPClient integration hangs on exit

[jsgsamzn]

Checks

• I have updated to the lastest minor and patch version of Strands
• I have checked the documentation and this is not expected behavior
• I have searched ./issues and there are no duplicates of my issue

Strands Version

1.26.0

Python Version

3.13.9

Operating System

macOS 15.7.3

Installation Method

pip

Steps to Reproduce

math_mcp_server.py:

"""Math MCP server implemented with mcp library"""

import math
from pydantic import Field


from mcp.server import FastMCP

# Create a server instance
mcp = FastMCP(name="MathServer")


@mcp.tool(description="Calculates the cosine of x.")
def cosine(x: float = Field(description="The value of x in radians")) -> float:
    """Cosine tool"""
    return math.cos(x)


@mcp.tool(description="Calculates the sine of x")
def sine(x: float = Field(description="The value of x in radians")) -> float:
    """Sine tool"""
    return math.sin(x)


if __name__ == "__main__":
    mcp.run()

mcp_managed_client.py:

"""Basic local MCP client"""

import logging

from mcp import stdio_client, StdioServerParameters
from strands import Agent
from strands.tools.mcp import MCPClient

logger = logging.getLogger(__name__)

logging.basicConfig(level=logging.DEBUG, format="%(asctime)s - %(name)s - %(levelname)s - %(message)s")


def get_agent():
    stdio_mcp_client = MCPClient(
        lambda: stdio_client(StdioServerParameters(command="python", args=["math_mcp_server.py"]))
    )

    new_agent = Agent(tools=[stdio_mcp_client])

    return new_agent


#### BEGIN EXAMPLE THAT HANGS ON EXIT
def main():
    agent = get_agent()
    # agent("Sine 1.2 rads?") # Problem occurs regardless if you call the agent or not.


if __name__ == "__main__":
    main()
#### END EXAMPLE THAT HANGS ON EXIT

#### BEGIN EXAMPLE THAT DOES NOT HANG ON EXIT
# agent = get_agent()
#### END EXAMPLE THAT DOES NOT HANG ON EXIT


print("DONE")

Final logger statements after printing "DONE":

2026-02-19 11:11:44,670 - strands.tools.mcp.mcp_client - DEBUG - removed provider consumer, count=0
2026-02-19 11:11:44,670 - strands.tools.mcp.mcp_client - DEBUG - no consumers remaining, cleaning up
2026-02-19 11:11:44,670 - strands.tools.mcp.mcp_client - DEBUG - [Thread: MainThread, Session: 5ed09f9e-fab2-45eb-9b31-8b81f376682f] exiting MCPClient context
2026-02-19 11:11:44,670 - strands.tools.mcp.mcp_client - DEBUG - [Thread: MainThread, Session: 5ed09f9e-fab2-45eb-9b31-8b81f376682f] waiting for background thread to join

Expected Behavior

Script exits without hanging.

Actual Behavior

Script hangs on exit.

Additional Context

This was also observed using aws_iam_streamablehttp_client from mcp-proxy-for-aws

Explicitly calling mcp_client.stop() will also allow the script to exit properly.

Possible Solution

No response

Related Issues

No response

[jsgsamzn]

Confirmed fixed for my use case.