Valve has decided to remove Treasure Keys from Dota 2 and with the latest update are no longer sold in the store.
Additionally as of August 13, 2014, all basic treasures that were previously opened using a Treasure Key have been removed from the game and the Steam Community Market.
Valve also notes that those with unused Treasure Keys have until July 1, 2015 to redeem them or they will expire.
According to the patch notes, the new system works in the following way:
Treasure Keys can now be redeemed for a free unlocked Treasure of your choice. When you use the treasure key a new redemption menu will open. Immortal treasures and some older special event treasures are excluded from this menu, but otherwise the list of treasures is unrestricted. One key can be exchanged for any one treasure. As new treasures are added to the game, they will also be added to this menu.
For regular players this update will not matter much. However, it will come as bad news for traders and item collectors, who will now have to come up with a common currency to deal with.
On Reddit Dota 2 fans are speculating that the removal of the Treasure Keys is because of the game’s China version. China has strict rules when it comes to selling content in games and the notion of traders earning around makes them a bit jumpy.