Customers with an existing (premium) VaultWiki 3 license will be able to download VaultWiki 4 at no additional cost. Shortly after the release of VaultWiki 4, as has been mentioned before, you should expect a price increase. VaultWiki 3 users will have a grace period to select their platform of choice should they want to migrate immediately, while new purchases of VaultWiki 4 will likely be platform locked. Keep in mind there has not yet been an official announcement about this, so this information could very well change in the near future.