Source
You can watch the original reveal stream here.
Summary
StudioBside is taking over publishing,
Transfer procedure,
New UI,
Improvements,
Game mode changes,
Other changes,
New awakened characters,
New rearm,
New characters,
New skins,
New ship,
New origin rewards,
StudioBside taking over
We already knew that Nexon and StudioBside are parting ways - this means that starting from February, Counter Side will be handled only by StudioBside, but Nexon isn't out of the picture fully as they are one of the investors of StudioBside.
Transfer procedure

On 8th February, the JPN server will be merged into Global and KR will have its own server. No matter the version, you will be able to play it on one client - both mobile and PC.
SEA, TW, and CN versions won't be affected by the change.
New UI




A new UI will be introduced with the update on 8th February and it will make a lot of the screens clearer. Even the battle screen will get small changes, like changing the HP bars of allies units from green to white.
The new UI will be introduced on the 8th of February in Global/KR/JPN servers.
Improvements
Removal of dupes
You won't need dupes anymore to ascend a character from level 1 to 110. Dupes and their usage confused the users the most, so they removed the ability to use them to ascend characters.

Instead, dupes will now work like Constellations from Genshin Impact, but less impactful - each will give additional passive stats (need 6 dupes in total for max). In the current version, you can't replace the dupes with anything, but this might change in the future.
Also now that you can't use dupes to ascend, from levels 1 to 100, you will use normal cores and from 100 to 110 you will use Fusion Cores (same number as before). We don't know if Fusion Cores will also be needed to ascend N/R/SR characters from 100 to 110 or if it applies to just SSR and ASSR.
As for farmable N, R, SR, and SSR characters - you can use their dupes in the constellation system without any issues (no need to pull them).
Furthermore, Counter Pass won't give dupes anymore, but 60 Fusion Cores instead.
Here are the bonuses you get from 1 to 6 based on the example of Hilde above:
DMG Dealt +4%
DMG RDC+4%
Deployment resource refund +4%
DMG Dealt +2%
DMG RDC+2%
Deployment resource refund +2%
Future PVE contents will be designed without this system in mind, meaning that you will be able to clear the contents without dupes.
This system will be introduced on the 8th of February in Global/KR/JPN servers.
Game modes changes
General
Dimension Trimming will be combined with Shadow Hall and Relic Stages - all modes will be available from one screen and they will also make further changes to make those 3 the endgame places to farm equipment. Also, the Skip feature will be added to all 3,
You will be able to farm materials to craft Maze gear,
Free Contracts will be removed (no more Chess mode),
Challenge tickets will be removed and you will be able to skip the stages,
More farmable SR and SSR will be added to side stories.

Dive
it's possible that no longer you will need multiple squads,
it will be the prime roguelike mode,
no more seasons and instead daily you will obtain Eternium based on the maximum depth you've reached,
Artifacts will be made much stronger.

Danger Close:
Orochi and other bosses will be added,
Only 1 boss per season,
Season length changed to 3 weeks with a 2-week battle duration,
Battle Points leaderboard and rewards reworked.

Gauntlet
1 season will be split into two parts - each lasting 10 weeks,
Players who reached Diamond 5 at least will get the seasonal skin,
Replacer King will be the reward skin in the first season of the revamp,
Collaboration units will be excluded from ban/up system,
They are looking into Terror decks dominating the meta and thinking about how to change that. Their current plan is to add a starting barrier to ships but it's not confirmed yet.
Raids
New Raid bosses will be added,
Practice run for Guild Coop to be added,
The guild coop will be reworked during March-April.
Other changes
Rearm system changes - you won't need Unit Data anymore to upgrade character skills once you Rearm them,
All Task Planet Points you ever spend on Unit Data will be refunded,
Max level of the company will be increased from 100 to 200,
Mentor System will be removed and the rewards redistributed to other content,
They will rework the Cash Shop and remove bad value packages,
The first-time purchase bonus increased from 1.5x to 2.0x,
The price of the monthly package will be reduced from 17000 KRW to 9900 KRW, and at the same time the Admin Coins you get from it will increase from 3256 to 3300,
Friendly Merc system will be added in March,
seems you will be able to borrow characters from Friends.
Prestige skins

They will introduce special limited skins for those who spend a certain amount of Admin Coins during a period of time (20 weeks). Awakened Shin Jia skin will be the first skin there and it also comes with a unique login animation.
Currently, we don't have any information on how much AC you will need to spend to get the skin.
New Awakened characters

Awakened Ray (Defender)
Ray will focus on protecting allies from hitstuns, and will be released with Counter Pass on the 8th of February (in KR). Codename Nehemoth.

Awakened Rosaria (Sniper)
Awakened Rosaria will finally receive her awakening and its codename is Asmodeus. She will be released on the 8th of February (in KR) as a banner character.
You can watch her PV here.

Awakened Lyudmila (???)
Awakened Lyudmila will be released in March (in KR).
New Rearms

Rearmed Gaeun
To be released in February in the KR server. Volume UP! Gaeun will be focusing on buffing allied HRT Berry units.

Rearmed Kaci Bins
To be released in March and with her, we will also get a new ship - visible on the right.
Rearm Edith Twins
No image for her yet, but she will be getting her Rearm in April and it's confirmed she won't be a Tower anymore.
New Characters

Jin Bora
Just her image was revealed - she will be released in March.

Noel (Fenrir Squad)
Just her silhouette was shown. She will be released in March as a Counter pass unit.
New Skins

Laura, Nequitia, and Harab wedding skins. All three will be released on 8th March.
New Origin rewards

List of rewards that JPN, Global, and KR servers will get during February as part of the New Origin version:
2x Awakened Tickets (Selector)
1x Awakened Ticket (Random)
90 Fusion Cores
1x Adversary gears 4pc set
2x SSR Employee selector
3x Random SSR Employee
1x Operator Selector
1x Random Operator
2x SSR Ship Selector
1500x Quartz
100x Set Binary
4x T7 Britra Relic gear selector
4x T7 Inhibitor Relic gear selector
50x Free Banner Pulls.
Hololive collab

Hololive collab will be rerun for Global in February! For KR and JPN it will also become available for the first time.