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◈ Agents & Manager/2026-04-11Intermediate

Accelerating AI Agent Development with Gemma 4

A practical guide to building AI agents with Google's Gemma 4. Covers model size selection, function calling, structured JSON output, multimodal agents, and parallel tool execution with working code.

Gemma 422AI agents24function callingGoogle3open modelagent development

Google's Gemma 4, released on April 2, 2026, sets a new standard for open model agent development. Native function calling, structured JSON output, and system instructions — combined with multimodal input and extended context windows — give developers a capable foundation for building real-world agents without depending on proprietary APIs.

Why Gemma 4 Works Well for Agents

Effective agents need three things: the ability to call external tools reliably, a way to produce structured output that downstream systems can consume, and enough context capacity to maintain state across multi-step tasks.

Gemma 4 provides all three natively. And under Apache 2.0, you can deploy it commercially without licensing concerns — removing a constraint that has historically pushed developers toward closed models.

Matching Model Size to Agent Complexity

Not every agent needs the most capable model. Choosing thoughtfully reduces cost and latency.

E2B is appropriate for simple routing agents: input classification, straightforward information retrieval, real-time edge processing where latency matters more than depth.

26B MoE is the right choice for most production agents. Its Mixture of Experts architecture delivers strong accuracy relative to its compute cost, making it practical for high-volume business automation workflows.

31B Dense is for agents where accuracy is non-negotiable: complex code generation, nuanced analysis, high-stakes decision support. The additional compute cost is justified when quality directly affects outcomes.

Core Pattern: ReAct Agent with Gemma 4

The ReAct (Reasoning + Acting) pattern — think, act, observe, repeat — maps naturally to Gemma 4's function calling capabilities.

import vertexai
from vertexai.preview.generative_models import (
    GenerativeModel, FunctionDeclaration, Tool, Part
)
 
vertexai.init(project="YOUR_PROJECT_ID", location="us-central1")
 
# Define the tool set
web_search = FunctionDeclaration(
    name="web_search",
    description="Search the internet for current information on a topic",
    parameters={
        "type": "object",
        "properties": {
            "query": {"type": "string", "description": "The search query"}
        },
        "required": ["query"]
    }
)
 
get_stock_price = FunctionDeclaration(
    name="get_stock_price",
    description="Retrieve the current price of a publicly traded stock",
    parameters={
        "type": "object",
        "properties": {
            "ticker": {
                "type": "string",
                "description": "Stock ticker symbol (e.g., GOOG, AAPL)"
            }
        },
        "required": ["ticker"]
    }
)
 
calculate = FunctionDeclaration(
    name="calculate",
    description="Evaluate a mathematical expression and return the result",
    parameters={
        "type": "object",
        "properties": {
            "expression": {
                "type": "string",
                "description": "Mathematical expression as a string (e.g., '185.42 * 100')"
            }
        },
        "required": ["expression"]
    }
)
 
tools = [Tool(function_declarations=[web_search, get_stock_price, calculate])]
 
model = GenerativeModel(
    "google/gemma-4-31b-it",
    tools=tools,
    system_instruction="""You are a financial research assistant.
    Use available tools proactively to provide accurate, current information.
    Always verify numeric data with the appropriate tool before reporting it."""
)
 
def execute_tool(name: str, args: dict) -> dict:
    """Route tool calls to their implementations."""
    if name == "get_stock_price":
        # In production, call a real stock data API here
        return {"ticker": args["ticker"], "price": 185.42, "currency": "USD"}
    elif name == "calculate":
        # Safe evaluation - restrict to numeric operations only
        allowed_names = {"__builtins__": {}}
        result = eval(args["expression"], allowed_names)
        return {"result": result}
    elif name == "web_search":
        return {"results": [f"Search result for: {args['query']}"]}
    return {"error": "Unknown tool"}
 
def run_agent(user_message: str, max_iterations: int = 5) -> str:
    """Execute a ReAct agent loop until completion or max iterations."""
    chat = model.start_chat()
    response = chat.send_message(user_message)
    
    for _ in range(max_iterations):
        parts = response.candidates[0].content.parts
        function_calls = [p for p in parts if hasattr(p, 'function_call') and p.function_call.name]
        
        if not function_calls:
            return response.text  # No more tool calls — final answer
        
        # Execute all requested tools and collect responses
        function_responses = []
        for part in function_calls:
            fc = part.function_call
            result = execute_tool(fc.name, dict(fc.args))
            function_responses.append(
                Part.from_function_response(name=fc.name, response={"result": result})
            )
        
        response = chat.send_message(function_responses)
    
    return response.text
 
# Example usage
result = run_agent(
    "What is Apple's current stock price, and what would 50 shares cost at that price?"
)
print(result)

Multimodal Agents: Acting on What the Model Sees

Gemma 4's visual understanding enables agents that observe the environment through images or video and take actions based on what they detect.

from vertexai.preview.generative_models import GenerativeModel, Part, Tool, FunctionDeclaration
 
create_work_order = FunctionDeclaration(
    name="create_work_order",
    description="Create a maintenance work order when a defect is detected",
    parameters={
        "type": "object",
        "properties": {
            "severity": {
                "type": "string",
                "enum": ["low", "medium", "high", "critical"]
            },
            "defect_type": {"type": "string"},
            "location": {"type": "string"},
            "recommended_action": {"type": "string"}
        },
        "required": ["severity", "defect_type", "location", "recommended_action"]
    }
)
 
alert_supervisor = FunctionDeclaration(
    name="alert_supervisor",
    description="Send an alert to the floor supervisor",
    parameters={
        "type": "object",
        "properties": {
            "message": {"type": "string"},
            "urgency": {"type": "string", "enum": ["normal", "urgent", "emergency"]}
        },
        "required": ["message", "urgency"]
    }
)
 
# E4B works well for real-time edge inference in manufacturing
inspection_model = GenerativeModel(
    "google/gemma-4-e4b",
    tools=[Tool(function_declarations=[create_work_order, alert_supervisor])],
    system_instruction=(
        "You are a quality control inspector. Analyze product images and "
        "take action immediately if you detect any defects or anomalies. "
        "Use create_work_order for defects, alert_supervisor for critical issues."
    )
)
 
def inspect_product_image(image_path: str):
    with open(image_path, "rb") as f:
        image_bytes = f.read()
    
    chat = inspection_model.start_chat()
    response = chat.send_message([
        Part.from_data(mime_type="image/jpeg", data=image_bytes),
        "Inspect this product and take appropriate action if you detect any issues."
    ])
    return response
 
# inspect_product_image("line_capture_001.jpg")

Parallel Tool Execution for Speed

When an agent needs multiple data sources simultaneously, parallel execution dramatically reduces total latency.

import asyncio
from vertexai.preview.generative_models import GenerativeModel
 
async def run_market_research_agent(companies: list[str]) -> str:
    """
    Fetch data for multiple companies in parallel, then synthesize.
    Sequential execution: N * API_latency
    Parallel execution: API_latency (for any N)
    """
    # Fetch all market data concurrently
    async def fetch_company_data(ticker: str) -> dict:
        await asyncio.sleep(0.2)  # Simulates API call latency
        return {"ticker": ticker, "price": 185.0, "market_cap": "2.8T", "pe_ratio": 28.5}
    
    results = await asyncio.gather(*[fetch_company_data(c) for c in companies])
    
    # Now synthesize with a single model call using all collected data
    model = GenerativeModel("google/gemma-4-31b-it")
    prompt = "Compare these companies and identify which appears strongest:\n"
    for r in results:
        prompt += f"- {r['ticker']}: Price ${r['price']}, Market Cap {r['market_cap']}, P/E {r['pe_ratio']}\n"
    
    response = model.generate_content(prompt + "\nProvide a concise analysis in 3 paragraphs.")
    return response.text
 
result = asyncio.run(run_market_research_agent(["GOOG", "AAPL", "MSFT", "META"]))
print(result)

Structured Output for Pipeline Integration

Agents that produce unstructured text are hard to integrate with downstream systems. JSON output mode removes that friction.

import json
from vertexai.preview.generative_models import GenerativeModel, GenerationConfig
 
model = GenerativeModel("google/gemma-4-31b-it")
 
def classify_and_route_request(user_message: str) -> dict:
    """Classify an incoming request and route it to the appropriate handler."""
    response = model.generate_content(
        f"""Classify this customer request and determine routing:
 
        Request: "{user_message}"
 
        Return ONLY valid JSON matching this exact schema:
        {{
          "intent": "billing|technical_support|feature_request|complaint|general",
          "urgency": "low|medium|high|critical",
          "sentiment": "positive|neutral|negative",
          "key_entities": ["array of important nouns from the request"],
          "suggested_department": "string",
          "estimated_resolution_time": "string (e.g., '2 hours', '1-2 business days')"
        }}""",
        generation_config=GenerationConfig(
            response_mime_type="application/json",
            temperature=0.0
        )
    )
    return json.loads(response.text)
 
# Example
classification = classify_and_route_request(
    "My payment failed three times and I urgently need this resolved for a client demo tomorrow."
)
print(f"Intent: {classification['intent']}")
print(f"Urgency: {classification['urgency']}")
print(f"Route to: {classification['suggested_department']}")
print(f"ETA: {classification['estimated_resolution_time']}")

Practical Agent Design Principles

A few principles that make the difference between a demo agent and one that works in production:

Start with a narrow tool set. More tools means more opportunities for the model to call the wrong one. Add tools incrementally as needs become clear.

Match model size to stakes. Not every decision needs the 31B Dense model. Build a routing layer that sends simple requests to cheaper models and complex ones to the strongest.

Always validate structured output. Even with response_mime_type="application/json", schema validation before processing is worth the overhead.

Log reasoning chains. Gemma 4's verbose intermediate responses are debugging gold. Store them — they make agent failures diagnosable.

Wrapping up

Gemma 4 brings production-grade agent capabilities to the open model ecosystem. Function calling, structured output, multimodal input, and long context — available commercially, deployable anywhere — represent a meaningful shift in what open model agent development can accomplish.

Start with a focused use case, choose the model size that fits your constraints, and build from there.

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