for how long does Pulumi store backup and history for stacks in backend (Azure/AWS)? are there any limitations ? or it is unlimited and depends on our backend lifecycle rules ?

are you using Pulumi’s managed state storage? or your own bucket?

own bucket

no there are no limitations, but you’re responsible for managing it yourself. you will need to turn on bucket versioning and manually map the checkpoint file to an object in the bucket. in the service, you can just retrieve it from the activity log