Google Antigravity SDK 0.1.16

Changelog: Default Gemini 3.8 Flash model upgrade, lightweight agent configuration, and Vertex AI Express mode

The 0.1.16 release updates the default model for new agents to gemini-3.8-flash for enhanced reasoning capabilities, introduces a .lightweight() method on agent configs for small and local models, adds Vertex AI Express mode with API keys, and expands tool runner support for callable classes and dataclass functors.

Improvements(8)

• Default model update to Gemini 3.8 Flash: The default model for new agents and configurations has been updated to gemini-3.8-flash, delivering higher reasoning quality and stronger task performance. Developers can override this default by specifying model in their configuration:
• Optimized lightweight agent configuration: New .lightweight() method on agent configurations (including LocalAgentConfig and LiteRTAgentConfig) applies preset optimizations for smaller, local-running models by configuring minimal tool sets, minimal prompting, and disabling background subagents:
• Vertex AI Express Mode (API key support): Developers can now connect to Vertex AI using Express mode by providing an API key directly on LocalAgentConfig(vertex=True, api_key="..."), simplifying authentication without needing full GCP project/location ADC setup:
• Support for callable class and dataclass tools: The SDK's ToolRunner now inspects and executes tools defined as callable class instances (functors) and dataclass methods, enhancing flexibility for custom tool implementations:
• OS sandbox opt-in for commands: Added an enable_sandbox field to RunCommandConfig to allow developers to execute terminal commands within an OS-level sandbox environment:
• Tool invocation argument flexibility: ToolWithSchema and public callable proxies now accept both positional (args) and keyword arguments (*kwargs), matching standard Python function calling conventions.
• Support for genai.Content Media: Introduced a structconverter to support media blocks from genai.Content objects within the SDK, enabling richer multimodal interactions.
• MCP dependency compatibility widening: The SDK now supports both mcp>=1.0 and mcp dependencies.

Fixes(3)

• Stop hook integration: Agents now support the StopHook lifecycle hook, triggered when an agent's execution is externally stopped, enabling custom cleanup and resource logging actions:
• Interactive example agent behavior: Fixed interactive SDK examples (interactive_cli.py, human_in_the_loop.py) to consistently configure AgentBehavior.INTERACTIVE.
• Tool runner stdio MCP environment: Resolved an issue in exported SDK examples where stdio MCP servers failed by ensuring child processes use sys.executable within the active virtual environment.

Patches(1)

• Step token usage deprecation: Deprecated Step.usage_metadata in favor of consolidated turn-level (ChatResponse.usage_metadata) and session-level (agent.conversation.total_usage) reporting.

<h3 class="