Though Borderlands 1 pre-dates the SHiFT Codes system, back in April of 2019 a remastered version of the game was released that contained graphical upgrades and the SHiFT System. This edition was called the "Game of the Year" and was given freely to anyone and everyone who had previously owned Borderlands 1.
Once the SHiFT System was incorporated into the game it was immediately put into the Classic Friday Rotation for SHiFT Codes and a Golden chest was added to Sanctuary. This meant that once every few weeks two new codes would be published for the game that rewarded 5 Golden Keys each giving players a total of 10 Golden Keys!
When new codes are published they generally last about 10-14 days before they expire. Below is a listing of all the currently active SHiFT Codes for Borderlands 1. They are displayed in reverse chronological order so that the most recent codes appear on top. If you see any code listed with an unknown expiration that means that they generally never expire. Every code can be redeemed one per player per platform.