This is pretty big news. Apparently, there is a way to get Eevee to evolve into your favourite choice between Jolteon, Flareon and Vaporeon through an actually rather simple procedure.
Reddit user TheAztek posted to Reddit a day ago stating that they think they figured out how to get Eevee to evolve into your evolution of choice. The post reads:
“Still needs full confirmation, but I think there is a way to determine which Eeveelution you get. Name your Eevee either Pyro, Sparky or Rainer before you evolve it in order to get a Flareon, Jolteon or Vaporeon, respectfully.”
In their edit, they say that they’ve tried this on 5 different Eevee’s, and each time they’ve gotten exactly the Pokemon they wanted. Apparently, the nicknames are a reference to the original Pokemon show episode “The Battling Eevee Brothers”.

In the episode, Ash and the gang come across the titular Eevee brothers – Rainer, Pyro and Sparky. Respectively, these brothers have a Vaporeon, a Flareon and a Jolteon. As you might have guessed, entering the nicknames of the brother that corresponds with your desired evolution is the secret to getting the Eeveelution you want.

Along with TheAztek, many other users on Reddit have also confirmed the technique works. This more recent post here by user smithnigel talks about the nickname trick as well, and is the main thread for current updates about the trick. A number of users have commented on the post about their success with the trick. For example, user GDK224 wrote:
“I only tried it once because I only had one to evolve and I’ve gotten a flareon and vaporeon already. I decided to try this to get a jolteon and, what do you know, I got a Jolteon. “

Another user, touchet29, also confirms it worked for him and his coworkers:
“Two people at my job tried this. Both named their’s Pyro and evolved into Flareon. I will test it out and edit this when I find one more Eevee.
Edit: Third person tried it with Rainer and got a Vaporeon!
Edit#2: Named my 613 Eevee, Pyro and it evolved into a 1520 Flareon. You, sir, are doing Arceus’s work.”
User strongscience62 actually provided a video of the process for further evidence. Check it out below.

The video above does only show one Eevee evolution, and thus, it could have been random luck that the Vaporeon matched the nickname of Rainer. More video tests over the coming days will probably arise to add more evidence that the trick works.
There may also be a caveat to the trick too. On the same thread, user Robotic_Chimera wrote:
“First one named Rainer, turned into Vaporeon. Second one named Rainer, turned into Flareon.
Edit: Tried a third one named Rainer, another Flareon.
Edit: Fourth Eevee tried, this one named Sparky. Evolved into Jolteon.
Can confirm this either does not work, or ONLY works on the first attempt.”
It appears you may only be able to use the nickname trick to get your first of each of the evolutions. After that, the process appears to go back to being randomised. Other Reddit users also seem to corroborate this opinion.
“However, as a further point, user DatapawWolf wrote that users who had trouble with the nickname trick may have done so due to server problems. Their post states: For the players reporting that their naming didn’t work, I would suggest, on a hypothesis, that they should rename their Eevee, then close and restart the application to ensure that the name is fully registered on the server, and then evolve.
My hypothesis is that the desired eevelution may not occur if there is potential for a greater delay between the server accepting a name (assuming that all Pokemon nicknames are stored on the server) and writing it, and when a player hits Evolve in their client, forcing the server to perform some immediate function on the Eevee.”

So, there you have it. It would seem that a large majority of people have success with this trick, and those that it didn’t work for may have actually experience server issues with the name change before clicking evolve.
As for whether this trick works for multiple copies of an Eeveelution, or just the first time you get one, more testing will have to be done. For now though, get out there, catch some Eevees and try this trick out for yourself!