Deltatraveler is NOT, I REPEAT NOT, An AU.
An AU is where you change characters around (Underswap, Deltarune Chapter Rewritten, etc) Or change aspects about characters (Underfell, etc).
Deltatraveler is NOT these things.
It is a hypothetical FANGAME.
There is a large difference between an AU and a Fangame.
A Fangame is a game based on a game. An AU is a concept of a “What if we did this…” Scenario. Some AU’s have fangames for them.
Deltatraveler is a stand alone fangame. NOT an AU.
Do some fangames have AUs for them…?
(Hoping for Underswap yellow)
I mean, not really…?
Thats not really how it works. That would be sick, but undertale yellow is a fangame, and underswap is its own thing. someone new could collab with the creators of undertale yellow to make that.
Deltatraveler is what I would call an AT (Alternate Timeline)
YES! THIS PERSON IS CORRECT!
YOUR RIGHT
You’re an au
YOUR
WRONG
Oh
Oops
A different timeline is quite literally a separate version of the universe
If it can’t happen in the Undertale universe then the universe must be changed in some way so that it can happen
There isn’t a need to be pedantic about ATs versus AUs
It would be nice to have a way to differentiate between the two types of fanon content, though, so you don’t really need to argue about this. If somebody wants to classify things better than you want to, let them do so.
Okay but then people can’t go thinking it’s objective and the line is frequently blurred
Ok but there's a clear difference tho. It's not a "gray area"
I didn’t say the words “gray area” but I probably would say them
What’s Dusttale
Sans remembers every timeline even when the world is erased there
Is it an AU or an AT
What’s Horrortale
Horrortale is supposed to take place in a normal timeline that exists in Undertale which wouldn’t be an AU or AT but it also uses the creator’s headcanons
Inverted Fate starts at the end of the pacifist route and then turns into a new world where everybody is the same person but also led completely different lives
Deltatraveler, by the original posts logic, is an AU.
It is a hypothetical what if we put Susie, Kris, and Noelle into different worlds.
yes, but…no
please stop my brain is melt
Also, Deltarune counts as an AU.
No, Undertale is an AU of deltarune. Ideas have priority, even if they aren’t released t the public. 
ERM ACKSHUALLY THEY WOULD BE AUS OF EACHOTHER 
No.
Toby never intended Undertale to be part of Deltarune prior to Undertale’s creation.
So therefore, Deltarune is the AU.