Once the Gold is used to unlock a Premium Upgrade, that upgrade will remain permanently unlocked from that point onwards, throughout all reincarnations. However you will still need to meet other requirements to use them - for example if a premium building upgrade requires 10 upgrades of lower tier, you will need to make those first. Upgrades cost between 2 and 12 File:Gold Icon.png; unlocking all premium building upgrades costs 435 File:Gold Icon.png. Below is a summary of the premium upgrades, for more detailed information, click the upgrade name to go to that page.