diff --git a/samples/python/scenarios/a2a/human-present/x402/run.sh b/samples/python/scenarios/a2a/human-present/x402/run.sh
new file mode 100755
index 00000000..3135833b
--- /dev/null
+++ b/samples/python/scenarios/a2a/human-present/x402/run.sh
@@ -0,0 +1,136 @@
+#!/bin/bash
+
+# A script to automate the execution of the x402 payment example.
+# It starts all necessary servers and agents in the background,
+# and then runs the client.
+
+# Exit immediately if any command exits with a non-zero status.
+set -e
+
+# Default payment method
+PAYMENT_METHOD="x402"
+
+# Parse command-line arguments
+while [[ "$#" -gt 0 ]]; do
+    case $1 in
+        --payment-method) PAYMENT_METHOD="${2:?--payment-method requires an argument}"; shift ;;
+        *) echo "Unknown parameter passed: $1"; exit 1 ;;
+    esac
+    shift
+done
+
+export PAYMENT_METHOD
+
+# The directory containing the agents.
+AGENTS_DIR="samples/python/src/roles"
+# A directory to store logs.
+LOG_DIR=".logs"
+
+if [ ! -d "$AGENTS_DIR" ]; then
+  echo "Error: Directory '$AGENTS_DIR' not found."
+  echo "Please run this script from the root of the repository."
+  exit 1
+fi
+
+if [ -f .env ]; then
+  set -a
+  source .env
+  set +a
+fi
+
+USE_VERTEXAI=$(printf "%s" "${GOOGLE_GENAI_USE_VERTEXAI}" | tr '[:upper:]' '[:lower:]')
+if [ -z "${GOOGLE_API_KEY}" ] && [ "${USE_VERTEXAI}" != "true" ]; then
+  echo "Please set your GOOGLE_API_KEY environment variable before running."
+  echo "Alternatively, set GOOGLE_GENAI_USE_VERTEXAI=true to use Vertex AI with ADC."
+  exit 1
+fi
+
+# Set up and activate a virtual environment.
+echo "Setting up the Python virtual environment..."
+
+if [ ! -d ".venv" ]; then
+  uv venv
+fi
+
+# Detect the correct activation script path based on the operating system
+case "$OSTYPE" in
+  msys* | cygwin*)
+    # Windows (Git Bash, MSYS2, or Cygwin)
+    source .venv/Scripts/activate
+    ;;
+  *)
+    # Unix/Linux/macOS
+    source .venv/bin/activate
+    ;;
+esac
+echo "Virtual environment activated."
+
+echo "Installing project in editable mode..."
+uv pip install -e .
+
+# Create a directory for log files.
+mkdir -p "$LOG_DIR"
+
+# This function is called automatically when the script exits (for any reason)
+# to ensure all background processes are terminated.
+cleanup() {
+  echo ""
+  echo "Shutting down background processes..."
+  if [ ${#pids[@]} -ne 0 ]; then
+    # Kill all processes using their PIDs stored in the array.
+    # The 2>/dev/null suppresses "Terminated" messages or errors if a process is already gone.
+    kill "${pids[@]}" 2>/dev/null
+    wait "${pids[@]}" 2>/dev/null
+  fi
+  echo "Cleanup complete."
+}
+
+# Trap the EXIT signal to call the cleanup function. This ensures cleanup
+# runs whether the script finishes successfully, fails, or is interrupted.
+trap cleanup EXIT
+
+# Explicitly sync to ensures the virtual environment is up to date.
+echo "Syncing virtual environment with uv sync..."
+if uv sync --package ap2-samples; then
+  echo "Virtual environment synced successfully."
+else
+  echo "Error: uv sync failed. Aborting deployment."
+  exit 1
+fi
+
+# Clear old logs.
+echo "Clearing the logs directory..."
+rm -rf "$LOG_DIR"
+mkdir -p "$LOG_DIR"
+
+# Start all the remote agents & servers.
+pids=()
+
+echo ""
+echo "Starting remote servers and agents as background processes..."
+
+# uv sync is explicitly run before starting any agents.
+# Prevent servers starting in parallel from colliding by trying to sync again.
+UV_RUN_CMD=("uv" "run" "--no-sync")
+
+if [ -f ".env" ]; then
+  UV_RUN_CMD+=("--env-file" ".env")
+fi
+
+echo "-> Starting the Merchant Agent (port:8001 log:$LOG_DIR/merchant_agent.log)..."
+"${UV_RUN_CMD[@]}" --package ap2-samples python -m roles.merchant_agent >"$LOG_DIR/merchant_agent.log" 2>&1 &
+pids+=($!)
+
+echo "-> Starting the Credentials Provider (port:8002 log:$LOG_DIR/credentials_provider_agent.log)..."
+"${UV_RUN_CMD[@]}" --package ap2-samples python -m roles.credentials_provider_agent >"$LOG_DIR/credentials_provider_agent.log" 2>&1 &
+pids+=($!)
+
+echo "-> Starting the Card Processor Agent (port:8003 log:$LOG_DIR/mpp_agent.log)..."
+"${UV_RUN_CMD[@]}" --package ap2-samples python -m roles.merchant_payment_processor_agent >"$LOG_DIR/mpp_agent.log" 2>&1 &
+pids+=($!)
+
+echo ""
+echo "All remote servers are starting."
+
+echo "Starting the Shopping Agent..."
+"${UV_RUN_CMD[@]}" --package ap2-samples adk web --host 0.0.0.0 "$AGENTS_DIR"
diff --git a/samples/python/src/common/config.py b/samples/python/src/common/config.py
new file mode 100644
index 00000000..bde355fe
--- /dev/null
+++ b/samples/python/src/common/config.py
@@ -0,0 +1,20 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Central configuration for LLM model settings."""
+
+import os
+
+DEFAULT_MODEL = "gemini-2.5-flash"
+MODEL = os.environ.get("MODEL", DEFAULT_MODEL)
diff --git a/samples/python/src/common/function_call_resolver.py b/samples/python/src/common/function_call_resolver.py
index 49356429..cfa80eba 100644
--- a/samples/python/src/common/function_call_resolver.py
+++ b/samples/python/src/common/function_call_resolver.py
@@ -26,6 +26,7 @@
 from google import genai
 from google.genai import types
 
+from common.config import MODEL
 
 DataPartContent = dict[str, Any]
 Tool = Callable[[list[DataPartContent], TaskUpdater, Task | None], Any]
@@ -81,7 +82,7 @@ def determine_tool_to_use(self, prompt: str) -> str:
     """
 
     response = self._client.models.generate_content(
-        model="gemini-2.5-flash",
+        model=MODEL,
         contents=prompt,
         config=self._config,
     )
diff --git a/samples/python/src/roles/merchant_agent/sub_agents/catalog_agent.py b/samples/python/src/roles/merchant_agent/sub_agents/catalog_agent.py
index b40f72e0..871e8e61 100644
--- a/samples/python/src/roles/merchant_agent/sub_agents/catalog_agent.py
+++ b/samples/python/src/roles/merchant_agent/sub_agents/catalog_agent.py
@@ -43,6 +43,7 @@
 from ap2.types.payment_request import PaymentOptions
 from ap2.types.payment_request import PaymentRequest
 from common import message_utils
+from common.config import MODEL
 from common.system_utils import DEBUG_MODE_INSTRUCTIONS
 
 
@@ -68,7 +69,7 @@ async def find_items_workflow(
         """ % DEBUG_MODE_INSTRUCTIONS
 
   llm_response = llm_client.models.generate_content(
-      model="gemini-2.5-flash",
+      model=MODEL,
       contents=prompt,
       config={
           "response_mime_type": "application/json",
diff --git a/samples/python/src/roles/shopping_agent/agent.py b/samples/python/src/roles/shopping_agent/agent.py
index 37c91a31..c453c323 100644
--- a/samples/python/src/roles/shopping_agent/agent.py
+++ b/samples/python/src/roles/shopping_agent/agent.py
@@ -26,13 +26,14 @@
 from .subagents.payment_method_collector.agent import payment_method_collector
 from .subagents.shipping_address_collector.agent import shipping_address_collector
 from .subagents.shopper.agent import shopper
+from common.config import MODEL
 from common.retrying_llm_agent import RetryingLlmAgent
 from common.system_utils import DEBUG_MODE_INSTRUCTIONS
 
 
 root_agent = RetryingLlmAgent(
     max_retries=5,
-    model="gemini-2.5-flash",
+    model=MODEL,
     name="root_agent",
     instruction="""
           You are a shopping agent responsible for helping users find and
diff --git a/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/agent.py b/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/agent.py
index 446f83fe..e51bcc8c 100644
--- a/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/agent.py
+++ b/samples/python/src/roles/shopping_agent/subagents/payment_method_collector/agent.py
@@ -26,12 +26,13 @@
 """
 
 from . import tools
+from common.config import MODEL
 from common.retrying_llm_agent import RetryingLlmAgent
 from common.system_utils import DEBUG_MODE_INSTRUCTIONS
 
 
 payment_method_collector = RetryingLlmAgent(
-    model="gemini-2.5-flash",
+    model=MODEL,
     name="payment_method_collector",
     max_retries=5,
     instruction="""
diff --git a/samples/python/src/roles/shopping_agent/subagents/shipping_address_collector/agent.py b/samples/python/src/roles/shopping_agent/subagents/shipping_address_collector/agent.py
index 0407b2b6..a5129d79 100644
--- a/samples/python/src/roles/shopping_agent/subagents/shipping_address_collector/agent.py
+++ b/samples/python/src/roles/shopping_agent/subagents/shipping_address_collector/agent.py
@@ -27,11 +27,12 @@
 """
 
 from . import tools
+from common.config import MODEL
 from common.retrying_llm_agent import RetryingLlmAgent
 from common.system_utils import DEBUG_MODE_INSTRUCTIONS
 
 shipping_address_collector = RetryingLlmAgent(
-    model="gemini-2.5-flash",
+    model=MODEL,
     name="shipping_address_collector",
     max_retries=5,
     instruction="""
diff --git a/samples/python/src/roles/shopping_agent/subagents/shopper/agent.py b/samples/python/src/roles/shopping_agent/subagents/shopper/agent.py
index d380fac7..9d536562 100644
--- a/samples/python/src/roles/shopping_agent/subagents/shopper/agent.py
+++ b/samples/python/src/roles/shopping_agent/subagents/shopper/agent.py
@@ -25,12 +25,13 @@
 """
 
 from . import tools
+from common.config import MODEL
 from common.retrying_llm_agent import RetryingLlmAgent
 from common.system_utils import DEBUG_MODE_INSTRUCTIONS
 
 
 shopper = RetryingLlmAgent(
-    model="gemini-2.5-flash",
+    model=MODEL,
     name="shopper",
     max_retries=5,
     instruction="""