Hi there!
Let's get the bad news out of the way: this update is
only partially compatible with older save-games (saves will load, but it'll be buggy). It's possible to rollback to 1.2.5 to finish your game if you need to. I'll explain how-to in this very article.
As usual, the full change-log is at the bottom of this post.
Now, let's get to the good stuff!
[h2]Dynamic Raid System[/h2]
It's not really a secret that the event system was starting to show some cracks, especially when it comes to enemy raids. Until now, ATC was relying on an extensive list of semi hard-coded raiding groups, which would unlock as the player discovers technologies or reaches population thresholds. Each time I added a mob to the game, I also needed to add a new "raid" file for that mob to show up, and it would interfere with other events (more raid files = other event less likely to spawn). In short, it was really getting increasingly messy as I added more content.

Well, it's all over! Raids are now dynamically generated using your base's firepower as a metric to determine their intensity. If you have a bunch of machine-gun wielding soldiers in exo-armor, you'll get much stronger opponents than when you're just a bunch of unarmed civilians.
The enemy distribution is also more varied, but will keep making sense (no zombies allying bandits or silly things like that). There's also more variety in the way raiders behave and enter your base. Some might move as an organized group, others will enter the base in mass from a whole side of your map, and so on.
Additionally, The raids' strength and ratio compared to other events is now configurable in the event settings.

A fair warning, this is a very big change in how ATC is handling difficulty and game balance. Standard difficulty is less forgiving. Traps and turrets will be necessary in the late game. Don't be afraid to tune down raid frequency and difficulty if you feel like it's too much, no one is going to judge you for it. 😉
[h2]Reworked Event Distribution[/h2]
Alongside the raid-related changes, I also reviewed how events are distributed and sent at the player. One of the problems before this update was that some mid/late game quest-lines would rarely trigger due to the sheer amount of raids/events the game could pick. Now, the game will try (whenever possible) to select events in a more varied way, avoiding repetitions.
[h2]New Mobs[/h2]
New critters join the roster. Two giant red ant types (worker and soldier), faster and hit a bit harder than black ants, however they have less armor and health. Red and black ants hate each other, and the concept will continue to be expanded upon in the future 1.3 content update.

I also added two giant beetle type mobs. They are slow and decently armored. They can drop eggs if you have the animal care technology, and can be pastured for defense or for food. They can't be used as pet.
Finally, a new cave spider replaces the normal ones underground. It's very slightly stronger than its counterpart.
You may also notice more mob infighting (red and black ants hate each other for instance).
[h2]World Map AI Hunting Parties[/h2]
Other main factions (like the Federation, Brotherhood, ...) can now send hunting parties against hordes they consider hostile if they have the firepower to defeat them. This should help keeping the world map zombie population under control, and it gives you an incentive to keep them around.
I intend to add more AI vs AI interactions like this in the future.
[h2]Savegame & Mod Compatibility[/h2]
I want to apologize to the new players, as there's a large influx of you guys due to the current discount. I promise, it's not in my habits to break saves, this is just very poor timing. But here we are, and I'd rather release this now before you guys gets too far into the game.
While you can still technically load older save-games, the game will be buggy if you do so. AI controlled factions will no longer behave as they should; main factions won't expand; beast-based raids will use the Raider-AI instead of the Fauna-AI; many of the bug fixes and changes won't apply or will only partially apply until you start a new game.
If you want to finish your pre-1.2.8 game, you can roll back to 1.2.5. To do so:
1) Right click on After the Collapse in your library, select "Properties"
2) Click on the "Betas" tab, and in the drop down menu, select the 1.2.5 version
3) Close and wait for Steam to roll back the update.
Mods altering or adding factions will need to be altered to be compatible with 1.2.8.
[h2]Future Plans[/h2]
Outside of maintenance patches (bug fixes), this will be the last patch in the 1.2x "Rebirth" series. Next major update will be 1.3. It should introduce rare procedurally generated weapon variants (unique to each playthrough), new ant-related biomes, events, late game crisis, alongside new in-game activities and constructions.
I will also be working on a large DLC, more info coming soon.
Cheers!
[h2]Full Changelog[/h2]
Artificial Intelligence- Other AI factions seek and destroy hostile hordes within their sphere of influence if they have the manpower for it.
- During some of the raids, enemies may move as a group with a leader instead of just zerging the base.
Game Balance- Dynamic event system (what handles raids, recruits, and other random events) was fully rewritten.
- Event difficulty settings are a lot more impactful and better balanced.
- New formula to evaluate the relative strength between 2 agents, or groups for expeditions.
- Relative raid difficulty can be set to start low and gradually increase over time.
- Added a flag to the gigantic boss-type mobs to make them immune to falling traps.
- Reduced black ant soldiers' "armor" rating a bit as it was too tanky for an entry level enemy.
New Content- Enemy raid compositions are procedurally generated, you'll see way more combinations of mobs.
- Added "Cave Spider", equivalent to a normal giant spider with its own graphics, a bit of armor, and living mostly underground.
- Two giant beetle mobs added to the enemy roster. Beetles can also be pastured and butchered for food.
- Added a few different animal "factions" which should lead to occasional mob infighting.
- Various biome related changes to increase mob diversity.
- The "Truce" diplomatic option with raiders is more useful (will prevent raids, and make world-map bandits ignore your assets)
- Two new ant-type mobs added to the enemy roster (fast/weak and slow glass cannon).
Game Engine- Event delivery balanced by multiple additional factors.
- Complete overhaul of the raid system, most raids are procedurally generated, removed now useless files.
- Reworked faction files to incorporate the new improvements. This will cause some diplomacy-related bugs in existing save-games, mods altering/adding main factions need a minor update.
- Minor performance improvements (load times, mostly)
Graphics- Some more new/replaced melee weapon hit animations.
- Replaced some of the world map vehicle sprites (AI factions).
User Interface- Added POI combat info directly to main POI menu, replacing the stars.
- Reworked one of the overlay filters to see survivors/enemies' name, health, and current activity all at once.
- Reworked "Event Difficulty" panel in the scenario selector's difficulty settings.
Bug Fixes- Inconsistencies when killing a trading vehicle from another faction. Now they'll properly declare war on you for doing so if they can.
- Issue where a faction flagged as "always hostile" would end up neutral to another faction if it's added later into the game.
- Misc issues in the Halloween scenario (missing events).
- Logic issue in friend/foe detection that was causing issues between animals and (not-owned) doors.
- Typo "Regenative Tissues" -> "Regenerative Tissues".
- Multiple issues with event balancing after loading a game.
- Save files in the save/load screen weren't always sorted properly.
- Missing french translation for some of the mobs
- Some structures, when being disassembled, would not play an animation.
- Area of Effect traps wouldn't always behave as intended.
- Oversized world map vehicle for some AI factions.
- Infected enemies getting "infected again" by the Pandemonium virus (zombies becoming tribal bug).
- Possible crash when using a zone as a template to copy a bunch of constructions in one go (obscure, power user bug)
- Fire on top of non burnable walls could still spread (fire going through walls bug)