The server backend is based on the current retail technology
The data used for the game is based off the 1.12.1 patch
The official patch for the game is known as 1.13
The client is based on a fork of the 7.3.5 Legion client
Classic WoW will be supported for as long as retail is around
Classic will release in Summer 2019
Classic will be part of your regular subscription
There will be no LFG/LFR tool
No cross-realm grouping
No Phasing
16 Debuff limit
Content release will be pseudo-progressive (4 stage release cycle)
AQ Gate opening event and Scourge invasion will happen
Flightpaths will be linked
Whats changing?
The graphics: Since the client is based off the current retail technology, players can utilise the latest graphical options including full widescreen support (NB This does not include new models or animations)
Loot trading for a 2hr window after looting will be in Classic
Sharding will be used in a limited capacity at server launches
The UI API will be a customised (cut-down) version of current API and not the 1.12 API
The modern mail system and UI will be used (ie right click add item to mail, multi mail etc)
Accessibility options: Colourblind mode from current retail will make its way to Classic
Right click reporting: This feature from retail will make its way to Classic
Battle.Net Integration: You will download the client from the BNet client and can chat with friends through it as per retail
No support for 32bit Clients
Whats not changing?
The graphics: Blizzard have included a Classic mode graphics option, which dials all your settings back to 2006
Rogue energy regen will tick in units of 20 per 2s as per Vanilla
Mail will take 1 hour to arrive still
The speculation:
The mount system will be based off the pre 1.11 system, where training is cheap but mounts themselves are expensive
Current UI addons will work with Classic, since the version of WoW API will be the same across Classic and retail.
The data used for the game is based off the 1.12.1 patch, so this should mean
1.12.1 talents
1.12.1 gear itemisation
1.12.1 quest hubs and flight paths
I've never played the old game - what's so different to today?
There is only 1 difficulty for all content
Talents are acquired every level and not once per ~15 levels (see references for expected talent trees)
Changing your spec costs an increasing amount of gold each time with a decay over time (like Reforging now)
Your first mount is available at level 40 not 20 - expect to run. A lot.
Iconic class abilities are not given at level 10 instead these are usually 31 point talents (first available at level 40)
There is no dungeon queuing system or teleport to dungeons - You must build your group via the LFG channel and travel to the dungeon yourself
Only classes with a healing spec have worthwhile self heals (except Warlocks of course) - Bandages are important
The stat system is quite different secondary stats award percentage changes, not a rating system
Threat management Over-aggroing the tank is a real possibility in Classic
Epic quality gear generally only comes from raids
Questions
Q. Will I be able to buy gold via Tokens? A. No
Q. Will there be store mounts/pets? A. No
Q. Will there be dual spec in Classic? A. Not 100% confirmed, although highly unlikely given what Blizzard have said
Q. Will Classic be included with your normal sub or separate? A. Included with the normal sub
Q. Will there be future content after Naxxramas? A. Not planned at this time, although not ruled out entirely
Q. Which version of AV are we getting? A. Not known at this time
Q. Will Battlegrounds be released at launch? A. No. They will come in the second wave of content
Q. Will there be any cross-over between Classic and retail such as title or appearances earned in Classic being available in retail? A. No
Q. Is FrontStabbing possible? A. No
Q. Will there be a separate Classic only subscription? A. No
Some quotes from Blizzard
J. Allen Brack: Our goal is to recreate that classic 1-60 gameplay. Some things changed as time went on, with different patches. How does that get manifested? That's one of the outstanding questions. But yeah, the goal is to recreate that exact experience, for better or for worse.
Dev Watercooler 2: From the beginning of this project, the teams mission has been to be as faithful as possible to World of Warcraft as it existed back in 2005 and 2006