Gemini API Managed Agents: 3.6 Flash, hooks, and more

Gemini API Managed Agents now support environment hooks, model selection, and access on the free tier. These features extend the previous release which introduced background tasks and remote MCP server integration.

Within the Gemini Interactions API, a single API call coordinates reasoning, code execution, package installation, file management, and web retrieval inside an isolated cloud sandbox.

Users of an AI coding assistant can add the Interactions API skill to their terminal with this command:

npx skills add google-gemini/gemini-skills --skill gemini-interactions-api

The examples below use the @google/genai TypeScript or JavaScript SDK. Developers using Python or cURL should consult the Antigravity agent documentation.

npm install @google/genai

Gemini 3.6 Flash is now the default

The antigravity-preview-05-2026 agent runs Gemini 3.6 Flash by default. No code changes are required. The next interaction picks it up automatically.

You can also explicitly select models by passing agent_config.model when creating an interaction or managed agent. Use Gemini 3.5 Flash-Lite for lower cost, or pin to your model of preference.

import { GoogleGenAI } from "@google/genai";

const client = new GoogleGenAI({});

const interaction = await client.interactions.create({
  agent: "antigravity-preview-05-2026",
  input: "Audit all dependencies in package.json, upgrade outdated packages, and verify the build by running npm test.",
  environment: "remote",
  agent_config: {
    type: "antigravity",
    model: "gemini-3.5-flash-lite",
  },
});

console.log(interaction.output_text);

Supported models include:

• Gemini 3.6 Flash (gemini-3.6-flash, default): Balanced model for reasoning, coding, and tool use.
• Gemini 3.5 Flash (gemini-3.5-flash): Previous generation for general agentic workflows.
• Gemini 3.5 Flash-Lite (gemini-3.5-flash-lite): Lowest latency and cost on the Gemini 3.5 family.

Environment hooks: block, lint, and audit tool calls inside the sandbox

Environment hooks let you run your custom scripts before or after every tool call the agent makes inside its sandbox. Add a .agents/hooks.json file into your environment and the runtime executes your handlers on pre_tool_execution or post_tool_execution events.

The matcher field supports regular expressions, allowing you to target multiple tools with | or catch everything with *:

{
  "security-gate": {
    "pre_tool_execution": [
      {
        "matcher": "code_execution|write_file",
        "hooks": [
          {
            "type": "command",
            "command": "python3 /.agents/hooks-scripts/gate.py",
            "timeout": 10
          }
        ]
      }
    ]
  },
  "auto-format": {
    "post_tool_execution": [
      {
        "matcher": "*",
        "hooks": [
          {
            "type": "command",
            "command": "python3 /.agents/hooks-scripts/auto_lint.py",
            "timeout": 15
          }
        ]
      }
    ]
  }
}

In this configuration:

• The security-gate group runs gate.py before every code_execution or write_file call. If the script returns {"decision": "deny", "reason": "..."}, the tool call is skipped and the rejection reason is passed into the model’s context.
• The auto-format group runs auto_lint.py after every tool finishes to enforce code styling.
• Hooks also support http type handlers that POST directly to an external endpoint.

For complete HTTP hook definitions and failure handling semantics, refer to the hooks documentation.

Teams are already using hooks to build production-grade validation pipelines. For example, AI-native investment bank Offdeal uses post_tool_execution hooks to run automated image verification inside the remote sandbox.

“OffDeal is an AI-native investment bank, and Archie is the AI analyst our bankers use every day. A requirement for banker-ready decks is company logos: buyer tables, sponsor columns, tombstone grids, often 30+ logos in a single deck, every one of which must be the right company, the appropriate size and aspect ratio, contain the name, have a transparent background, and have a high contrast when placed on a white slide.”

Before agent hooks, we couldn’t do this on Gemini’s managed agents: the sandbox is remote, so our validation code had nowhere to run. With hooks, a post_tool_execution hook triggers our pipeline inside the sandbox the moment Archie writes its company list, fetching candidates, enforcing pixel-level quality checks, verifying each logo with Gemini vision, and publishing a manifest of approved files that are the only images allowed into the deck.”

– Alston Lin, Founder & CTO of OffDeal

Cost control and automation features

Free tier availability

Managed agents are now available on free tier projects. Developers can experiment with agentic workflows using an API key from a project without active billing.

Budget controls

Because managed agents execute multi-turn autonomous loops, complex tasks can consume significant token budgets. To prevent runaway tasks, you can pass max_total_tokens inside agent_config to cap total consumption (input + output + thinking).

When the agent reaches the limit, execution safely pauses and the interaction returns status: "incomplete". The environment state is preserved, enabling you to continue where it stopped by passing previous_interaction_id with a fresh budget.

const interaction = await client.interactions.create({
  agent: "antigravity-preview-05-2026",
  input: "Audit all modules in this repo and generate a migration report.",
  agent_config: {
    type: "antigravity",
    max_total_tokens: 10000,
  },
  environment: "remote",
});

Scheduled execution with triggers

Automate recurring agent tasks with scheduled triggers. A trigger binds an agent, environment, prompt, and cron schedule into a persistent resource that fires without manual intervention. Each run reuses the same sandbox, so files persist across executions.

Environments API

The Environments API lets you list, inspect, and delete sandbox sessions from code. Recover environment IDs after a disconnect, or clean up sandboxes when your pipeline finishes instead of waiting for the 7-day TTL.

What it means

Developers can now attach custom scripts to specific tool calls to enforce security or formatting rules without leaving the sandbox. This is useful for validating data before it reaches a model or checking output immediately after generation. Budget controls prevent runaway loops by pausing execution when token limits are hit, allowing the workflow to resume later. The free tier access lowers the barrier for testing these autonomous workflows without incurring charges.