It is one of the great unsolved mysteries of the Warhammer 40,000 universe — at least, it was. Via a new codex, Games Workshop has finally revealed the true nature of the much-debated Terminus Decree — and some Warhammer 40,000 lore fans really wish it hadn’t.
The Terminus Decree, for the uninitiated, is the final order issued to the Grey Knights, perhaps the most mysterious chapter of Space Marines in the setting, before the Emperor was placed within the Golden Throne following his mortal wounding by the Warmaster Horus at the end of the Horus Heresy.
(For more on the Emperor's current... situation, check out this article here.)
The idea is that only the Supreme Grand Master of the Grey Knights can open The Terminus Decree and discover what, exactly, this final order entails. Essentially, it’s a ‘break glass in case of emergency’ Pandora's box — and Warhammer 40,000 fans have wondered what was inside for years.
Now, with the release of the new Grey Knights codex (a book packed with background lore, pictures of miniatures for use on the tabletop game, and fresh rules to play around with), Games Workshop has for the first time revealed what The Terminus Decree actually involves.
Warning! Spoilers for Warhammer 40,000 lore follow:
A single passage in the new Grey Knights codex has lit up Warhammer 40,000 lore fans, as it reveals the ultimate duty of the Grey Knights is to either kill or re-entomb the Emperor within the Golden Throne, should he ever attempt to leave, be reborn, or ascend to godhood. This is The Terminus Decree: an ultra-secret doomsday device, a contingency box left by the Emperor himself that would have the Grey Knights force him back onto the Golden throne, should he ever recover and dare to leave it.
New Grey Knights Codex "explains" The Terminus Decree
— Tôryk BirdThrowa (@Torykbirdthrowa) July 29, 2025
...what?
WHAT!?
HOW!
WHEN!?
H O W!? pic.twitter.com/87h9wjeQPB
Interestingly, the passage reveals The Terminus Decree offers no guidance for how the Grey Knights should do this, if they ever have to, and that they might have to cut through the Adeptus Custodes to do it. The Custodes are the Emperor’s super powerful bodyguard — even more powerful than the Space Marines — so good luck with that!
This is a huge amount for any Warhammer 40,000 lore fan to take in. It is a major revelation, one that puts an end to years of debate at this point. Whether you take it as the Emperor being smart because he knew that if he were ever to return it simply wouldn’t be him but something else entirely (this development would potentially tap into ongoing The Dark King plotline), or Games Workshop planting seeds for something big they’re building towards (Chief Custodian Constantin Valdor looms large over the setting, and it does seem like the Emperor is… stirring), the inescapable truth is now we know, whether we like it or not.
And that’s a big issue for some Warhammer 40,000 lore fans, who have since expressed their frustration that Games Workshop has explained this mystery at all. Warhammer 40,000 is packed full of unexplained mysteries, hanging plot threads, and tantalizing puzzles that it may never get around to explaining. Take, for example, the mystery of the II and XI, the Forgotten and the Purged, the two lost primarchs and their two lost legions. Games Workshop has danced around revealing this part of Warhammer 40,000 lore for years, and many hope the truth is never revealed. Speculation is, after all, part of the fun. There is much to be said for leaving things to the imagination.
And that was the case with The Terminus Decree, until now. So what gives? Why reveal it now? Why take the speculation and imagination away from fans on this lore point in particular? There is much vehement reaction from the community. Here’s a snippet:
“I don't really like this,” redditor aposi said. “It both spoils the mystery and changes the concept from a weapon of last resort in a doomsday scenario (which is cool to speculate about) to just trying to restore the status quo in the event one of those cool speculative things happens.”
There has never been a case where GW filled in lore that was better than just leaving it up the the players imagination.
— Shadow of a Doubt (@Shadow_ofaDoubt) July 30, 2025
But this is by far the most atrocious example. Not even close.
“Dislike... outright annoyed by it,” added Drxero1xero. “Huge mystery, leave it unknown or make a novel or three out of it... Nope throw it away in text box in a codex.
“GW are little by little sucking the fun out of warhammer's settings, flat and colorless... no mystery, all little bites of lore…”
GW is lost, they're just going to explain everything and take the mystery out of things aren't they?
— Gage Davidson (@GageDavidson608) July 30, 2025
“I feel like this not only completely undermines the whole mystery, but it doesn't even work. At all,” said TheVoidDragon.
“The cool thing about the lore was not quite knowing what it was, what it would do, or what it was even about. The mystery and speculation on what it could be was what made it intriguing for so many years. To now just outright define it takes all that way completely, it's just plainly stated exactly what it is as if it doesn't matter.”
Leaving mysteries is essential to the mystique of 40k. If a mystery must be revealed, it must be a magnificent piece of writing. In this case, they marble brained one of the most foreboding and cool things the grey knights had. FFS GW
— LazySternguard (@LazySternguard) July 30, 2025
The next obvious question is, will The Terminus Decree come into effect any time soon? Will we see, perhaps in a novel, another codex, or a blog post, the Grey Knights actually fight the Custodes because the Emperor has somehow revived himself? Or is this just an odd spike of activity in Warhammer 40,000 lore that causes a kerfuffle now, but won’t lead to anything for years to come?
Like the Warp itself, Games Workshop sometimes feels unknowable.
The God-Emperor, by John Blanche. Image credit: Games Workshop.
Wesley is Director, News at IGN. Find him on Twitter at @wyp100. You can reach Wesley at wesley_yinpoole@ign.com or confidentially at wyp100@proton.me.
