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Gemini API: New Antigravity Agent Version, Gemini 3.8 Flash GA and Model Deprecations

Google's Gemini API replaced antigravity-preview-05-2026 with antigravity-preview-09-2026 on 17 September (the old version shut down on 5 October), made Gemini 3.8 Flash generally available on 2 September, limited Gemini 2.5 access to recent users, and deprecated gemini-3.1-flash-image. What developers need to change.

If you build on Google's Gemini API, September 2026 brought a few changes that require action.

Antigravity agent: 09-2026 replaces 05-2026

On 17 September, Google introduced antigravity-preview-09-2026, replacing antigravity-preview-05-2026 — the API version of the agent behind Google's Antigravity coding platform. (What Is Google Antigravity?)

  • The old agent was deprecated the same day and shut down on 5 October 2026. Requests naming it now fail.
  • Remote sandbox users usually only need to change the agent string.
  • If you run tools locally (local_environment) or parse function_call steps, the built-in tool names and parameters changed — update your handlers.

Gemini 3.8 Flash is GA

gemini-3.8-flash became generally available on 2 September, followed by real-time Gemini 3.8 Live models (15 September) and 3.8 Flash TTS voice models (22 September). Several products moved their defaults: GitHub Copilot lists Gemini 3.8 Flash as the replacement for 3.7 Flash, and Lovable deprecated 3.6 and 3.7 Flash for its apps' AI features. (GitHub Copilot Model Deprecations)

Deprecations and access changes

  • Gemini 2.5 models (18 September): access limited to users who have used them recently. They aren't deprecated, but new projects should use 3.5 Flash-Lite or 3.8 Flash.
  • gemini-3.1-flash-image (6 October): deprecated without a shutdown date; Google recommends gemini-nano-banana-2.1.

What to do

  1. Search your code and config for antigravity-preview-05-2026, gemini-2.5, gemini-3.7-flash and gemini-3.1-flash-image.
  2. Move model names into configuration, not code, so the next swap is a one-line change. (Environment Variables Explained)
  3. Re-run your evals on the new model before switching production — newer isn't automatically better for your prompts. (Evaluate LLM Outputs)

The pattern across providers

Every major provider now ships model updates monthly and retires old ones on a few weeks' to a few months' notice. Anthropic is retiring Sonnet 4.5 on 30 November; GitHub retires several Copilot models on 19 October. Build for model churn. (Claude Sonnet 4.5 Retirement, Claude vs Gemini)

Source: Gemini API changelog

EasySpawn gives your AI app a server-side backend where model names, keys and fallbacks live in configuration — and Claude Code can do the migration across your codebase. See how it works or join the waitlist.

Related: What Is Gemini CLI? · Claude Code vs Antigravity · What Is OpenRouter? · How to Build an AI App

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