Codes ยท Android, iOS, Windows
Undecember Codes: Active and Expired (June 2026)
Last checked May 28, 2026 (UTC)
Undecember codes drop around updates and events in this hack-and-slash ARPG, and most of them hand you free diamonds and growth items. I track the working ones here, and we refresh the list whenever new ones land.
Undecember codes are coupons the Undecember team posts on the official social channels and during update events for free Red Diamonds (the premium currency), gold, and rune or gear materials. Undecember is a dark hack-and-slash ARPG built around a flexible rune system, where you slot skill and link runes to craft your build. Red Diamonds buy convenience and stash space, gold handles crafting, and materials power your gear. Codes speed up the rune and gear progression that's basically what your character's strength comes down to.
Quick tip. Honestly, spend your code Red Diamonds on stash and inventory space before cosmetics. This is a loot-driven ARPG where juggling runes and gear is the whole game, so more room lets you hold and craft the pieces your build needs, while a cosmetic does nothing for your power.
New Undecember codes show up during major updates, new season launches, and milestone events. They follow the usual ARPG rhythm, so they're live for a while and then they expire. You redeem them in game through the coupon option in the menu or on the official redemption page, and they're case sensitive.
- Redeem in game through the coupon option or on the official page.
- Most codes give you Red Diamonds, gold, and materials.
- They expire when the event window closes, so don't sit on them.
- Each one is single use per account.
- Capitalization matters. Use the Copy button so you don't fat-finger it.
Active Undecember codes (4)
Tap the Copy button next to each code. They're case sensitive, so paste rather than type. And redeem early, because they expire once the event window's done.
| Code | Reward |
|---|---|
| UNDECEMBER2026 New Expires soon | Red Diamonds and materials |
| RUNEGIFT Expires soon | Red Diamonds |
| HACKSLASH Expires soon | Gold and materials |
| UNDUPDATE Expires soon | Red Diamonds bundle |
If a code says invalid, it either expired or you've already used it. Check the official Undecember channels for the current set.
Expired Undecember codes
Skip these. They were tied to old launch windows and seasonal events, so they won't work now.
| Code | Reward | Expired |
|---|---|---|
| UNDLAUNCH | Launch Red Diamonds | 2025 |
| UNDSUMMER25 | Summer gold | September 2025 |
| UNDWINTER25 | Holiday Red Diamonds | January 2026 |
How to redeem Undecember codes
Undecember handles redemption two ways: in game through the coupon option in the menu, or on the official redemption page. Either way, your rewards land in the in-game mailbox.
In game (coupon option)
- Open Undecember and find the coupon option in the menu.
- Type the code exactly as shown, case and all.
- Confirm to redeem, then open your mailbox to claim the rewards.
On the official redemption page
- Open the official Undecember coupon page in any browser.
- Sign in with the account tied to your character.
- Enter the coupon code and confirm.
- Launch the game and check your mailbox for the rewards.
If a code gets rejected, it's almost always because it expired or you already used it on this account. Since these codes are case sensitive, paste from the Copy button to rule out a typo.
Undecember codes FAQ
What do Undecember codes give you?
Mostly Red Diamonds, gold, and rune or gear materials. Red Diamonds buy convenience and stash space, gold handles crafting, and materials power your gear. The rewards speed up the rune and gear progression that defines your character's strength.
How should I spend code Red Diamonds?
On stash and inventory space before cosmetics. This is a loot-driven ARPG where managing runes and gear is the whole point, so more space lets you hold and craft the pieces your build needs, while a cosmetic does nothing for your power.
Why does my code keep failing?
Usually one of three things. It expired, you already redeemed it on this account, or you mistyped it. These codes are case sensitive, so paste from the Copy button to keep the exact form.
Where do I redeem Undecember codes?
Two spots. In game through the coupon option in the menu, or on the official Undecember coupon page in a browser. Both drop the rewards into your in-game mailbox, ready to claim.
Do codes work on the PC client?
Yes. Undecember is cross-platform, so your account is shared between PC and mobile. Redeem on either one and the Red Diamonds and materials apply to the same character no matter where you play.
Where do I find the newest Undecember codes?
Follow the official Undecember social channels and keep an eye on in-game events. New Undecember codes drop during updates, new seasons, and milestones, and the official channels post them first, usually with the patch notes.