Gemini-3.1-flash-lite: implicit cache stopped applying cost savings (~June 30 2026)

Gemini API
1

Since ~June 30, 2026, implicit context caching stopped applying its cost
discount for gemini-3.1-flash-lite on my project.

  • Before ~June 30 my effective input rate was ~$0.16 / 1M tokens (implicit
    cache applying the ~90% discount on my stable ~50K-token system prefix).
  • Since June 30 billing shows input at the full standard rate ($0.25 / 1M),
    no “cached input” SKU, and Savings = $0.00 — even though API responses
    still report cached_content_token_count > 0 (~16%) in usage_metadata.
  • My code and request pattern have NOT changed.

Questions:

  1. Is this a known regression with implicit caching for Gemini 3.x?
  2. Why does usage_metadata report cached tokens while billing applies no
    cache discount (Savings $0.00)?
  3. What is the recommended way to restore cache savings for
    gemini-3.1-flash-lite — is explicit caching (caches.create) the
    supported path?
2

Hello @IQkamikadze,

I have DM’ed you for details.

3

Hi I made a post regarding this issue which seemed to happen around the time when Gemini 3.6 flash was released. I found that the minimum requirement for the caching to kick in is around 100k and it ONLY cache the first ~80k! I just checked today and it’s still not working as it used to.

This is totally not acceptable from Google if they wanted companies to adopt gemini for commercial productions. If my app was live, I could be losing money thanks to this issue with implicit caching because it would have increased my cost by 100% even with all of the mitigation to deal with their current caching behavior.

Anyone else experiencing this issue?