I purchased ¥1,000 of prepay credits on September 1, 2026.
In the credit transaction history, I see:
2026/09/01 - 09/30 Google Cloud -¥492
2026/09/01 Consumption tax -¥49
Ending balance ¥459
So ¥492 was deducted as usage.
However, both the AI Studio cost graph and the Cloud Billing report
show only ¥296.47 for September 1-6 (which is the entire period I have
used the API - today is September 6):
Charges ¥296.47 - Cost savings ¥0.00 = Total cost ¥296.47
The Cloud Billing SKU breakdown also totals ¥296.468197 with ¥0 tax:
Generate content output token count gemini 3.8 flash text batch 542,044 ¥162
Generate content output token count gemini 3.8 flash text 144,971 ¥87
Generate content input token count gemini 3.8 flash text batch 216,694 ¥13
Generate content output token count gemini 3.7 flash text 17,289 ¥10
Generate content input token count gemini 3.8 flash text 64,073 ¥8
Generate content input token count gemini 3.8 flash image batch 119,919 ¥7
Generate content input token count gemini 3.8 flash image 35,471 ¥4
Generate content input token count gemini 3.7 flash text 17,468 ¥2
Generate content cached input token count gemini 3.8 flash text 120,997 ¥1
Generate content input token count gemini 3.7 flash image 9,732 ¥1
Generate content cached input token count gemini 3.8 flash image 66,967 ¥1
Subtotal ¥296.468197 / Adjustments ¥0 / Tax ¥0 / Total ¥296.468197
I verified the token counts against usage_metadata returned by the API
and they match, so the reported usage itself looks correct.
Question: what accounts for the ¥196 difference between the -¥492
credit deduction and the ¥296.47 shown in the cost reports?
Is there a category of charge that is deducted from prepay credits but
does not appear in the Cloud Billing SKU report?
Account: Prepay, Gemini Developer API, google-genai Python SDK.