Gemini 2.5 Retirement on Oct 16: What the Swap Costs

Gemini 2.5 Pro, Flash and Flash-Lite retire on Vertex AI on October 16, 2026, eleven days from now. The Gemini 2.5 retirement is a budget problem before it is an engineering one: the replacements cost more per token, and the Flash tier doubles its price on January 1.

Gemini 2.5 retirement: what Google announced

The Vertex AI release notes say it plainly: "The retirement dates for Gemini 2.5 Pro, Gemini 2.5 Flash-Lite, and Gemini 2.5 Flash have been updated to October 16, 2026." That entry is dated April 2, 2026.

The Gemini API is on a different track. The Gemini models page says Google is limiting 2.5 access to users who have actively used those models in the past, and that they stay served until further notice. For new projects it recommends Gemini 3.5 Flash-Lite or Gemini 3.8 Flash. So October 16 is a Vertex deadline. On the Gemini API there is no shutdown date, but you can't count on that for a new project.

What the Gemini 2.5 Flash-Lite and Flash swap costs

Prices are USD per 1M tokens, input / output, for text, from the Gemini API pricing page. Output prices include thinking tokens.

| Retiring | Price | Swap | Price | | --- | --- | --- | --- | | Gemini 2.5 Flash-Lite | $0.10 / $0.40 | Gemini 3.5 Flash-Lite | $0.30 / $2.50 | | Gemini 2.5 Flash | $0.30 / $2.50 | Gemini 3.5 Flash-Lite | $0.30 / $2.50 | | Gemini 2.5 Flash | $0.30 / $2.50 | Gemini 3.6 Flash | $0.75 / $3.75 through Dec 31, then $1.50 / $7.50 | | Gemini 2.5 Pro (prompts up to 200k tokens) | $1.25 / $10.00 | Gemini 3.1 Pro Preview (prompts up to 200k tokens) | $2.00 / $12.00 |

Three things stand out:

• Flash-Lite hurts most. Input triples and output is 6.25x. A pipeline that was nearly free becomes a line item.
• Flash users have a quiet exit. Gemini 3.5 Flash-Lite lists at the same price as Gemini 2.5 Flash. Whether it is good enough for your task is an eval question, not a pricing one.
• The Flash price doubles. Gemini 3.6, 3.7 and 3.8 Flash all list $0.75 / $3.75 through December 31, 2026, then $1.50 / $7.50. Budget for the January rate, not the launch rate.

Gemini 2.5 Pro to Gemini 3.1 Pro Preview is +60% on input and +20% on output. The Pro target is labeled Preview on the models page, which matters if your change process bans previews.

Run your own numbers

# USD per 1M tokens (text input, output incl. thinking), from the Gemini API pricing page
PRICES = {
    'gemini-2.5-flash-lite': (0.10, 0.40),
    'gemini-2.5-flash': (0.30, 2.50),
    'gemini-3.5-flash-lite': (0.30, 2.50),
    'gemini-3.6-flash (to Dec 31)': (0.75, 3.75),
    'gemini-3.6-flash (from Jan 1)': (1.50, 7.50),
}

input_m = 100   # millions of input tokens per month: replace with yours
output_m = 20   # millions of output tokens per month, thinking tokens included

for model, (p_in, p_out) in PRICES.items():
    print(f'{model:32} ${input_m * p_in + output_m * p_out:,.2f}/month')

With 100M input and 20M output tokens a month, that prints $18.00 for 2.5 Flash-Lite, $80.00 for 3.5 Flash-Lite, and $150.00 for 3.6 Flash, rising to $300.00 in January. Pull your real token counts from billing, since thinking tokens count as output.

Behavior changes that move the bill

The Gemini 3 developer guide lists changes that affect cost and quality:

• thinking_level replaces the legacy thinking_budget, and you cannot send both in one request.
• Keep temperature at its default of 1.0. Lower values can cause looping or degraded output.
• Gemini 3 defaults for PDFs may increase token usage.

If you manage chat history yourself, the thinking guide says to resend thought blocks exactly as received.

What to do before October 16

Find every hardcoded model ID

grep -rnE "gemini-2\.5-(pro|flash|flash-lite)" . \
  --exclude-dir=node_modules --exclude-dir=.git \
  --include="*.py" --include="*.ts" --include="*.yaml" --include="*.yml" \
  --include="*.tf" --include="*.json" --include=".env*"

This lists every file that names a 2.5 model, including config and Terraform. Add your own file types, and check secrets managers and CI variables, which grep can't see.

Run a bake-off, then price the winner

Replay a sample of real traffic through Gemini 3.5 Flash-Lite and Gemini 3.8 Flash. Add Gemini 3.1 Flash-Lite, which the pricing page lists at $0.25 / $1.50 for text, below 3.5 Flash-Lite. Compare quality and measured tokens per request, then feed the totals into the calculator.

For jobs that don't need an instant answer, the pricing page lists a 50% batch discount. For Gemini 3.5 Flash-Lite that is $0.15 / $1.25.

Gotchas

• The October 16 date comes from Vertex AI release notes. Check your own console for the exact status of your project.
• The prices above come from the Gemini API pricing page. Check Vertex AI pricing for the rates you actually pay.
• Audio input is priced separately. Flash-Lite 2.5 audio is $0.30, for example.
• Gemini 3.1 Pro is a Preview model today.

For teams running Gemini in production, October 16 is the deadline, but the January price doubling is the number that decides whether the swap quietly eats your margin.