From the docs:
Retrieval is priced at $0.20/GB per assistant per day. If your application stores 1GB of files for one day and passes it to two Assistants for the purpose of retrieval (e.g., customer-facing Assistant #1 and internal employee Assistant #2), you’ll be charged twice for this storage fee (2 * $0.20 per day). This fee does not vary with the number of end users and threads retrieving knowledge from a given assistant.
If I just upload files and don’t use them (i.e. do not run any assistant with file attached, and do not create messages with files), would it incur cost?
Also, only files attached to an assistant count as Retrieval, right? What about files attached to messages, they should count towards token, correct?