{"slug": "gemini-2-5-calls-reroute-to-gemini-3-on-dec-1-and-can-break-apps", "title": "Gemini 2.5 Calls Reroute to Gemini 3 on Dec. 1 and Can Break Apps", "summary": "Google will automatically reroute all Gemini Developer API requests to `gemini-2.5-pro` to `gemini-3.8-flash` and requests to `gemini-2.5-flash` to `gemini-3.5-flash-lite` on Dec. 1, 2026, according to the Gemini API changelog published Nov. 2, 2026, with billing following the new models' rates. Google listed four breaking changes for both deprecated models: function calling and `thought_signature` validation, `thinking_level` replacing `thinking_budget`, removal of sampling parameters, and removal of prefilled model turns; Firebase's Nov. 2 release notes said some settings will return 400 errors after the switch. Google advised developers to change the model string before Dec. 1, test function calling and `thought_signature` handling, swap `thinking_budget` for `thinking_level`, and strip sampling parameters and prefilled turns.", "body_md": "# Gemini 2.5 Calls Reroute to Gemini 3 on Dec. 1 and Can Break Apps\n\nChange the model string and drop thinking_budget and sampling parameters before Dec. 1, or Gemini 2.5 requests get rerouted to Gemini 3 models.\n\nAny app that still calls `gemini-2.5-pro` or `gemini-2.5-flash` through the Gemini Developer API will have those requests rerouted to Gemini 3 models on Dec. 1, with different billing and request rules. Google announced the change in its Nov. 2 Gemini API release notes ([Gemini API changelog, Nov. 2, 2026](https://aistudio.google.com/docs/changelog)).\n\n## What Google Said\n\nBoth models are deprecated and no longer selectable in Google AI Studio. “Effective December 1, 2026, all API requests to `gemini-2.5-pro` will automatically route to” `gemini-3.8-flash`, Google said, and billing follows Gemini 3.8 Flash rates. Requests to `gemini-2.5-flash` route to `gemini-3.5-flash-lite` at Flash-Lite rates.\n\nGoogle listed four breaking changes for both models:\n\n- Function calling and `thought_signature` validation\n- `thinking_level` replaces`thinking_budget`\n- Sampling parameters are removed\n- Prefilled model turns are removed\n\nGoogle’s migration advice: change the model string before Dec. 1, test function calling and `thought_signature` handling, swap `thinking_budget` for `thinking_level`, and strip sampling parameters and prefilled turns. It linked a migration guide for each target model.\n\nFirebase repeated the notice in its Nov. 2 release notes, and said some settings will return 400 errors after the switch.\n\n## The Take\n\nA silent reroute is a worse deal than a shutdown. A shutdown errors loudly on day one. A reroute keeps returning 200s from a different model with different pricing, and requests that use a setting the new model rejects fail with a 400.\n\nFirebase AI Logic apps that name a 2.5 model in client code are the likeliest to get caught. A shipped mobile build keeps its hardcoded model string until users update. Server code and Genkit flows change in one deploy.\n\nGrep every repo for `gemini-2.5` and for `thinking_budget`, `temperature`, `top_p` and `top_k` sent to those models. Ship the new model string in a test build now, not on Nov. 30. For mobile apps, the update lag means the work should start this week.", "url": "https://wpnews.pro/news/gemini-2-5-calls-reroute-to-gemini-3-on-dec-1-and-can-break-apps", "canonical_source": "https://firerun.io/gemini-2-5-reroute-dec-1-firebase-apps-2026/", "published_at": "2026-11-07 00:00:00+00:00", "updated_at": "2026-11-09 01:43:23.480492+00:00", "lang": "en", "topics": ["artificial-intelligence", "large-language-models", "ai-products", "developer-tools"], "entities": ["Google", "Gemini 2.5 Pro", "Gemini 2.5 Flash", "Gemini 3.8 Flash", "Gemini 3.5 Flash-Lite", "Gemini Developer API", "Google AI Studio", "Firebase"], "also_reported_by": [], "alternates": {"html": "https://wpnews.pro/news/gemini-2-5-calls-reroute-to-gemini-3-on-dec-1-and-can-break-apps", "markdown": "https://wpnews.pro/news/gemini-2-5-calls-reroute-to-gemini-3-on-dec-1-and-can-break-apps.md", "text": "https://wpnews.pro/news/gemini-2-5-calls-reroute-to-gemini-3-on-dec-1-and-can-break-apps.txt", "jsonld": "https://wpnews.pro/news/gemini-2-5-calls-reroute-to-gemini-3-on-dec-1-and-can-break-apps.jsonld"}}