[Bug]: Missing Gemini IMAGE tokens in cost calculation

[tremlin]

What happened?

If the Gemini API counts part of the input as IMAGE, then these tokens are not considered for the cost calculation. prompt_tokens as a total is correct, but this is not being used for cost calculation.

Example:

'usageMetadata': {'promptTokenCount': 262, 'candidatesTokenCount': 117, 'totalTokenCount': 1080, 'promptTokensDetails': [{'modality': 'TEXT', 'tokenCount': 4}, {'modality': 'IMAGE', 'tokenCount': 258}], 'thoughtsTokenCount': 701}, 'modelVersion': 'gemini-2.5-flash', 'responseId': 'M-C6aMH-Mq-nnsEPyrC6wAs'}

In the example from the screenshot you can see that the cost is calculated as:
0.002046 = 4 * 0.3 * 1e-6 + 818 * 2.5 * 1e-6
instead of
0.002124 = 262 * 0.3 * 1e-6 + 818 * 2.5 * 1e-6

Relevant log output

Are you a ML Ops Team?

No

What LiteLLM version are you on ?

v1.78.5

Twitter / LinkedIn details

No response

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[holtenko]

same issue, image tokens will not be included.