Google charges for that API calls additionally. The number are pretty high and cost me hundreds of dollars per month. Is there anything we can do to decrease the usage of GCS?
External Secrets Operator creates a lease for every secret sync. With multiple K8s clusters and over 500 secrets it was creating the leases constantly. Setting experimental-enable-vault-token-cache and setting longer TTLs to auth methods helped me to reduce the GCS API calls.
You might find it useful to also switch to batch type tokens whereever you can, as well.
They are not as flexible as service tokens, but they require no storage operations to create or validate, which may be particularly relevant in your scenario.
However, be aware that Vault does have various background processes that need to invoke ListObjects periodically - which seems unfortunate given the GCS storage pricing system :-/