Pompeii tickets

Why not purchase from the official site?
You don’t need to but you will likely pay more on Viator

I doubt they ever sell out

https://pompeiisites.org/en/

I had booked with Viator but read today that the official seller of
tickets has changed as of March.

As above, Viator has never been the 'official' ticket seller for this attraction or any other, for that matter. It doesn't mean that you don't have tickets but the link Christine has kindly provided is the official one with the correct pricing.

There is also the option of walk up ticket sales.

Were you getting something from Viator in addition to the tickets? We purchased our tickets when we arrived to the site.

We were hoping to get a tour which is why I originally looked on Viator. I looked on the official site but the October tickets are not up yet nor did I see tours.

Here's the info about tours provided by the scavi office:
https://pompeiisites.org/en/about-single-visitors/

You purchase these at the on-site ticket offices, and they depart from two different entrances; Porta Marina Superiore is the main entrance, nearest the Pompei Scavi - Villa dei Misteri train station. Piazza Anfiteatro is on the far eastern side of the site.

Yes, It's too early to pre-purchase tickets for October, and the tours noted above appear to only be purchasable onsite.

Another option that has been used by quite a number of forum posters:
https://www.sharedtours.com

Click: "Pompeii Walk: Two Hours from Pompeii", This is an economically priced group tour (6-16 people; likely to be smaller than larger) with the Rick Steves stamp of approval. You do not need to purchase an entry ticket in advance; you'd do that at the designated Porta Marina Inferiore entrance, which is not far from the Porta Marina Superiore entrance I mentioned about. Be sure to read the "How it Works" information regarding signing up, guide payment (cash only), etc. Bring a valid ID. It's not too early to add your name/names to the list for your desired date.

Another "Mondo" option that includes tickets:
https://www.mondoguide.com/city-tour/pompeii-walking-tour-with-an-archaeologist-2-hour-highlights-example-shared

Get there fairly early, walk up and buy your ticket.

Mid October you probably won't have a problem just walking up and buying tickets, that being said, I highly recommend a guided tour so you get an excellent overview of the ruins, then continue walking further on your own.

Are you going to the MANN museum or other scavi such as Herculaneum or Paestum? In which case, a 365 Lite Compania Arte Carte will save you quite a bit of money. We loved our 2.5 hour tour with Askos, this one includes the Villa of the Mysteries - (I should have added that it was with a qualified archaologist.) https://askostours.com/pompeii/pompeii-3-hour-small-group-tour-with-villa-of-the-mysteries/. Here's my TR, there's more info about the Lite Compania card & some other ideas about what to see inside Pompeii. And what to watch before you go, have a fantastic trip! https://community.ricksteves.com/travel-forum/trip-reports/great-trip-to-pompeii-naples-over-new-years-december-26-january-2nd-2026

I did a day tour called “small group tour of Herculaneum and Pompeii with an archaeologist “ which I purchased through Get Your Guide. It left from Naples, across from the train station.

Walking through these sites with someone who has the background knowledge to help you understand what you are seeing is quite valuable.

Thank you for all the comments. Will work on it further.

Just so the OP is aware, Get your Guide, like Viator, is a third party selling other companies' tours. While I hear far fewer issues with Get your Guide, it still is not the actual provider of the tour or the venue.

I agree with the advice to just purchase online at the official site. In October, you won't have any trouble getting in even if you had to buy a ticket on site. There are sometimes good reasons for using Viator or GYG for specific cases, but I would say Pompeii is not really on that list unless you really want to book a specific private tour in advance. Official guides are plentiful once you are inside the site, just join up with a tour and pay with cash