Vertex AI SDK: Gemini Model Configuration and Usage

Core Principles

The Vertex AI SDK provides Python interfaces for Gemini models with fine-grained control over generation behavior, safety, and response characteristics. Proper configuration is critical for production-grade agents.

Model Initialization (Required Pattern)

Basic Client Setup

from google import genai
from google.genai import types
import os

# Initialize Vertex AI client
client = genai.Client(
    vertexai=True,
    project=os.getenv("GOOGLE_CLOUD_PROJECT"),
    location=os.getenv("GOOGLE_CLOUD_LOCATION", "us-central1")
)

# Reuse client instance across requests
MODEL_ID = "gemini-2.0-flash-exp"

Best Practice: Initialize client once and reuse. Creating new clients for every request adds unnecessary overhead.

Model Selection Guide

Model	Use Case	Speed	Cost	Context Window
gemini-2.0-flash-exp	Fast responses, production agents	Fastest	Lowest	1M tokens
gemini-1.5-pro	Complex reasoning, analysis	Medium	Medium	2M tokens
gemini-1.5-flash	Balanced performance	Fast	Low	1M tokens

Generation Parameters (Configuration Pattern)

Core Parameters

from google.genai import types

# Create generation configuration
config = types.GenerateContentConfig(
    temperature=0.7,        # Randomness (0.0 = deterministic, 2.0 = creative)
    top_p=0.95,            # Nucleus sampling threshold
    top_k=40,              # Top-k sampling (limits token pool)
    max_output_tokens=2048, # Maximum response length
    candidate_count=1,      # Number of responses to generate
    stop_sequences=["END"]  # Optional: Stop generation at these tokens
)

# Use config with model
response = await client.aio.models.generate_content(
    model=MODEL_ID,
    contents="Explain quantum computing",
    config=config
)

Parameter Guidelines

Temperature (Controls randomness):

• 0.0-0.3: Deterministic, factual responses (documentation, data extraction)
• 0.4-0.7: Balanced creativity (general conversation, analysis)
• 0.8-1.2: Creative writing (stories, brainstorming)
• 1.3-2.0: Maximum creativity (experimental, art)

Top-P (Nucleus sampling):

• 0.9-0.95: Recommended for most use cases
• 0.8-0.89: More focused, less diverse outputs
• 0.96-1.0: Maximum diversity

Top-K (Token pool size):

• 1-10: Very focused (not recommended)
• 20-50: Balanced (recommended)
• 100+: Very diverse

Max Output Tokens:

• Set based on expected response length
• 512: Short responses (summaries, answers)
• 2048: Medium responses (explanations, code)
• 8192: Long responses (essays, documentation)

Safety Settings (Required Pattern)

Comprehensive Safety Configuration

from google.genai.types import (
    HarmCategory,
    HarmBlockThreshold,
    SafetySetting
)

# Define safety settings
safety_settings = [
    SafetySetting(
        category=HarmCategory.HARM_CATEGORY_HATE_SPEECH,
        threshold=HarmBlockThreshold.BLOCK_MEDIUM_AND_ABOVE
    ),
    SafetySetting(
        category=HarmCategory.HARM_CATEGORY_DANGEROUS_CONTENT,
        threshold=HarmBlockThreshold.BLOCK_MEDIUM_AND_ABOVE
    ),
    SafetySetting(
        category=HarmCategory.HARM_CATEGORY_HARASSMENT,
        threshold=HarmBlockThreshold.BLOCK_MEDIUM_AND_ABOVE
    ),
    SafetySetting(
        category=HarmCategory.HARM_CATEGORY_SEXUALLY_EXPLICIT,
        threshold=HarmBlockThreshold.BLOCK_MEDIUM_AND_ABOVE
    )
]

# Apply to generation config
config = types.GenerateContentConfig(
    temperature=0.7,
    safety_settings=safety_settings
)

Harm Categories

Category	Description	When to Block
HATE_SPEECH	Content promoting hate based on protected characteristics	Always
DANGEROUS_CONTENT	Instructions for harmful activities	Always
HARASSMENT	Content intended to bully, intimidate, or threaten	Always
SEXUALLY_EXPLICIT	Sexual content	Application-dependent

Threshold Levels

Threshold	Effect	Use Case
BLOCK_NONE	No blocking	Internal testing only
BLOCK_ONLY_HIGH	Block high-confidence harmful content	Liberal applications
BLOCK_MEDIUM_AND_ABOVE	Block medium+ confidence (RECOMMENDED)	Production
BLOCK_LOW_AND_ABOVE	Block low+ confidence	Conservative applications

Streaming Responses (Production Pattern)

Async Streaming Implementation

async def stream_response(prompt: str) -> None:
    """
    Generate streaming response with real-time output.

    Args:
        prompt: User prompt for the model
    """
    client = genai.Client(vertexai=True)

    # Use generate_content_stream for streaming
    async for chunk in client.aio.models.generate_content_stream(
        model=MODEL_ID,
        contents=prompt,
        config=types.GenerateContentConfig(temperature=0.7)
    ):
        # Process each chunk as it arrives
        if chunk.text:
            print(chunk.text, end="", flush=True)

    print()  # Newline after complete response

Streaming with Error Handling

import asyncio
from typing import AsyncIterator

async def safe_stream_response(
    prompt: str,
    timeout: float = 30.0
) -> AsyncIterator[str]:
    """
    Stream response with timeout and error handling.

    Args:
        prompt: User prompt
        timeout: Maximum time to wait for complete response

    Yields:
        Text chunks from the model
    """
    client = genai.Client(vertexai=True)

    try:
        stream = client.aio.models.generate_content_stream(
            model=MODEL_ID,
            contents=prompt
        )

        # Apply timeout to entire stream
        async for chunk in asyncio.wait_for(stream, timeout=timeout):
            if chunk.text:
                yield chunk.text

    except asyncio.TimeoutError:
        yield "\n[Response timed out]"
    except Exception as e:
        yield f"\n[Error: {str(e)}]"

# Usage
async for text in safe_stream_response("Explain AI"):
    print(text, end="", flush=True)

Why Streaming?

• Reduces perceived latency (first token arrives faster)
• Enables real-time UX (typing effect)
• Allows early termination if needed
• Better for long responses

Function Calling (Integration Pattern)

Basic Function Calling

from pydantic import BaseModel, ConfigDict, Field

# Define tool schema
class CalculatorInput(BaseModel):
    """Calculator tool input."""
    model_config = ConfigDict(strict=True)

    operation: str = Field(description="Math operation: add, subtract, multiply, divide")
    a: float = Field(description="First number")
    b: float = Field(description="Second number")

# Create function declaration
calculator_function = types.FunctionDeclaration(
    name="calculator",
    description="Perform basic math operations",
    parameters=CalculatorInput.model_json_schema()
)

# Create tool
calculator_tool = types.Tool(
    function_declarations=[calculator_function]
)

# Use with model
response = await client.aio.models.generate_content(
    model=MODEL_ID,
    contents="What is 15 multiplied by 23?",
    config=types.GenerateContentConfig(
        tools=[calculator_tool]
    )
)

# Check for function call
if response.candidates[0].content.parts:
    for part in response.candidates[0].content.parts:
        if part.function_call:
            print(f"Function: {part.function_call.name}")
            print(f"Args: {part.function_call.args}")

Automatic Function Execution Loop

async def run_agent_with_tools(
    user_message: str,
    tools: list[types.Tool],
    max_iterations: int = 5
) -> str:
    """
    Run agent with automatic function execution.

    Args:
        user_message: Initial user message
        tools: List of available tools
        max_iterations: Max tool call iterations

    Returns:
        Final text response
    """
    client = genai.Client(vertexai=True)
    chat = client.aio.chats.create(
        model=MODEL_ID,
        config=types.GenerateContentConfig(tools=tools)
    )

    response = await chat.send_message(user_message)

    for _ in range(max_iterations):
        # Check if model wants to call a function
        if not response.candidates[0].content.parts:
            break

        function_calls = [
            part.function_call
            for part in response.candidates[0].content.parts
            if part.function_call
        ]

        if not function_calls:
            break  # No more function calls

        # Execute all function calls
        function_responses = []
        for fc in function_calls:
            # Execute function (implement your tool execution logic)
            result = await execute_tool(fc.name, fc.args)

            function_responses.append(
                types.Part(
                    function_response=types.FunctionResponse(
                        name=fc.name,
                        response=result
                    )
                )
            )

        # Send function results back to model
        response = await chat.send_message(
            types.Content(parts=function_responses)
        )

    return response.text

Endpoint Selection (Regional vs Global)

Regional Endpoints

# US regional endpoint
client = genai.Client(
    vertexai=True,
    project="my-project",
    location="us-central1"  # Regional endpoint
)

Advantages:

• Data residency guarantees (data stays in region)
• Compliance with regional regulations
• Potentially lower latency for regional users

Use When:

• GDPR, HIPAA, or other compliance requirements
• Serving users in specific geographic region
• Data sovereignty requirements

Global Endpoints

# Global endpoint
client = genai.Client(
    vertexai=True,
    project="my-project",
    location="us"  # Global endpoint
)

Advantages:

• Higher availability
• Potential for better global latency
• Automatic failover

Use When:

• Global user base
• Maximum availability required
• No data residency constraints

Claude on Vertex AI (Special Case)

For Claude models on Vertex AI, endpoint selection affects both performance and cost:

# Regional endpoint required for Claude
client = genai.Client(
    vertexai=True,
    project="my-project",
    location="us-east5"  # Claude available in specific regions
)

model = "claude-3-5-sonnet@20241022"

Note: Check Vertex AI documentation for current regional availability of specific models.

Anti-Patterns to Avoid

Recreating Client for Every Request

# BAD: Creates unnecessary overhead
async def bad_generate(prompt: str):
    client = genai.Client(vertexai=True)  # New client every time!
    return await client.aio.models.generate_content(...)

# GOOD: Reuse client
CLIENT = genai.Client(vertexai=True)  # Module-level singleton

async def good_generate(prompt: str):
    return await CLIENT.aio.models.generate_content(...)

Ignoring Safety Settings

# BAD: No safety configuration
config = types.GenerateContentConfig(temperature=0.7)

# GOOD: Explicit safety settings
config = types.GenerateContentConfig(
    temperature=0.7,
    safety_settings=[...]  # Always configure
)

Not Handling Streaming Errors

# BAD: No error handling
async for chunk in stream:
    print(chunk.text)

# GOOD: Comprehensive error handling
try:
    async for chunk in asyncio.wait_for(stream, timeout=30):
        if chunk.text:
            print(chunk.text)
except asyncio.TimeoutError:
    handle_timeout()
except Exception as e:
    handle_error(e)

Vague Function Descriptions

# BAD: Generic, unhelpful description
function = types.FunctionDeclaration(
    name="get_data",
    description="Gets data",  # Not helpful!
    ...
)

# GOOD: Specific, actionable description
function = types.FunctionDeclaration(
    name="get_weather",
    description="Get current weather conditions for a specific city including temperature, humidity, and forecast",
    ...
)

When to Use This Skill

Activate this skill when:

• Configuring Gemini model parameters
• Implementing safety controls
• Building streaming response UIs
• Integrating function calling
• Selecting Vertex AI endpoints
• Tuning model behavior for specific use cases

Integration Points

This skill is a required dependency for:

• adk-fundamentals: Model configuration is part of agent setup
• prompt-engineering: Model parameters affect prompt effectiveness
• rag-patterns: RAG requires proper model configuration

Related Resources

For deeper understanding:

• Vertex AI Model Parameters: https://cloud.google.com/vertex-ai/generative-ai/docs/learn/prompts/adjust-parameter-values
• Safety Settings Guide: https://ai.google.dev/gemini-api/docs/safety-settings
• Function Calling Reference: https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/function-calling
• Streaming Guide: https://cloud.google.com/vertex-ai/generative-ai/docs/samples/generativeaionvertexai-stream-text-basic
• Claude on Vertex AI: https://docs.claude.com/en/api/claude-on-vertex-ai