From Archon Arcana - The KeyForge Wiki

If the active player has enough Æmber to forge a key during Step 1, they must do so. To forge a key, the active player spends Æmber from the Æmber pool on their identity card, returning it to the common supply. Then, that player flips any one of their key tokens over to its forged side, indicating that the key has been forged.

  • The default cost to forge a key is six Æmber. Some card abilities may increase or decrease this number.
  • No more than one key can be forged during this step each turn, even if the active player has enough Æmber to forge multiple keys.
  • Some cards have effects that allow Æmber on these cards to be spent when forging keys. If there is enough Æmber on cards with this effect you control combined with the Æmber in your Æmber pool to forge a key you must do so during Step 1.
Official rules v1.8 March 2021