Model migration
Gemini 2.5: migrate Pro and Flash before December
Google announced Gemini 2.5 changes on November 2. Review the December 1 automatic targets, parameters and costs before migrating.
In this article
Deprecated does not mean retired today. Before December 1, explicitly select and test the destination model; both the model behind an alias and its bill can change.
What changes, and when#
The November 2, 2026 notice removes Gemini 2.5 Pro and Flash from the AI Studio selector. From December 1, their API requests will route to the destinations below and be billed at those models’ rates. Do not infer that every 2.5 API call already fails today.
| Previous identifier | Destination from December 1 |
|---|---|
| gemini-2.5-pro | gemini-3.8-flash |
| gemini-2.5-flash | gemini-3.5-flash-lite |
Documentation: Google · Gemini API release notes, 2 November 2026 · Google · Gemini API deprecations
Audit the contract before renaming the model#
Changes include thinking_level replacing thinking_budget and validation of function calls and thought signatures. The migration guides also identify sampling parameters and prefilled model turns to remove. Check the API and SDK contract you actually use; changing a string does not prove compatibility.
| Area | Migration test |
|---|---|
| Parameters | Review thinking_level and remove parameters the destination does not accept. |
| Tools | Replay function calls and their responses; preserve required signatures. |
| Context | Test short inputs and inputs close to the limit your application uses. |
| Result | Validate schemas, errors and acceptance criteria in addition to HTTP 200. |
Documentation: Google · Gemini 3.8 Flash migration · Google · Gemini 3.5 Flash-Lite migration
A controlled test and a recovery path#
- Freeze a representative task set and its acceptance criteria; do not use private production data as test material.
- Run it in staging with an explicit destination ID and record effective model, usage, errors and elapsed time.
- Compare cost per completed task, including retries and additional fees. A lower token price does not establish a lower workflow cost.
- Roll out gradually with an already-tested compatible alternative. Do not rely on the old model name as a recovery option after it redirects.
What to preserve in the comparison#
Record the cutoff date, exact model ID, applicable price and cache and context conditions. Review alerts, budgets and rules tied to model names. This article covers these two migrations rather than the entire retirement calendar.