Up to 2 MB / 10,000 records. Keep each report in one currency. Include token counts, explicit rate snapshots and non-token charges.
What needs to be in the file?
event_id, at, provider, model, currency, input_tokens (includes cache reads and writes), cached_tokens, cache_write_tokens, output_tokens, extra_cost, and rates (input, cached, cache_write, output per million tokens plus source).