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.