All the Mods 10 launched on NeoForge for Minecraft 1.21, and the question everyone asks is whether it is worth moving from ATM9. The answer depends on what you value: familiar content, new mods, performance, or server stability. Here is how they compare.
The Basics
| ATM9 | ATM10 | |
|---|---|---|
| Minecraft version | 1.20.1 | 1.21.x |
| Mod loader | Forge | NeoForge |
| Mod count | ~400 | ~350 |
| Maturity | Fully stable | Active development |
| Java version | Java 17 | Java 21 |
ATM9 has been out long enough that most bugs are fixed, most mod interactions are documented, and the community knows the optimal progression paths. ATM10 is newer, which means more active development but also more patches, more config changes, and more surprises.
Mod Differences
What ATM10 Added
ATM10 benefits from mods that moved to NeoForge and 1.21:
- Newer Create builds with updated features and better performance
- NeoForge-exclusive mods that were never backported to Forge 1.20
- Updated world generation from Minecraft 1.21 changes
- Java 21 optimizations including Generational ZGC support
What ATM10 Lost (Temporarily or Permanently)
Not every mod has made the jump from Forge 1.20 to NeoForge 1.21:
- Some tech mods are still catching up. If your favorite niche mod is not in ATM10, it might not have updated yet.
- Certain compatibility patches between mods need time to be rewritten for NeoForge's changed API
- Recipe integrations and quest line polish are still being refined
Check the ATM10 mod list on CurseForge before committing. If a mod you consider essential is missing, stay on ATM9 until it arrives.
Core Mods in Both
The backbone of both packs is the same: Create, Applied Energistics 2, Mekanism, Thermal Series, Botania, Ars Nouveau, and the usual utility mods. If you play ATM for the core tech and magic progression, both packs deliver.
Performance
This is where the difference is measurable.
Server Performance
| Metric | ATM9 (Forge 1.20.1) | ATM10 (NeoForge 1.21) |
|---|---|---|
| Startup time | 3-5 minutes | 2-4 minutes |
| Idle RAM usage | 6-8 GB | 5-7 GB |
| Active RAM (4 players) | 8-12 GB | 7-10 GB |
| Average TPS (4 players) | 18-20 | 19-20 |
| Chunk generation speed | Moderate | Faster |
NeoForge's modernized loading pipeline and Java 21's improvements give ATM10 an edge in startup time and memory efficiency. The TPS difference is small, but ATM10 tends to hold 20 TPS more consistently because several core mods were optimized during the NeoForge port.
Client Performance
Client FPS depends heavily on your hardware and shader/resource pack choices, but ATM10 generally runs slightly better because:
- NeoForge's rendering pipeline is more efficient than legacy Forge
- Several rendering mods (Sodium ports, Embeddium) work better on the newer version
- Java 21's JIT compiler produces faster code
The difference is maybe 10 to 20% FPS improvement on the same hardware. Not transformative, but noticeable on mid-range machines.
Server Requirements
ATM9
| Players | RAM | CPU | Storage |
|---|---|---|---|
| 1-2 | 8 GB | 3.5 GHz+ single thread | 15 GB |
| 3-6 | 10-12 GB | 4.0 GHz+ single thread | 20 GB |
| 7-12 | 12-16 GB | 4.0 GHz+ fast single thread | 25 GB |
ATM10
| Players | RAM | CPU | Storage |
|---|---|---|---|
| 1-2 | 6 GB | 3.5 GHz+ single thread | 12 GB |
| 3-6 | 8-10 GB | 4.0 GHz+ single thread | 18 GB |
| 7-12 | 10-14 GB | 4.0 GHz+ fast single thread | 22 GB |
ATM10 is more memory-efficient, which means you can either save money on a smaller plan or use the same plan with more headroom. On Space-Node Minecraft hosting, the Premium tier with Ryzen 9 9950X is the strongest option for either pack. The fast single-thread performance directly translates to stable TPS in kitchen-sink modpacks.
Stability
ATM9
Stable. Years of patches, known issues documented, workarounds established. If you start an ATM9 server today, you will have a predictable experience. The pack receives maintenance updates but no major changes.
ATM10
Actively developing. You will get patches every few weeks, some of which may change recipes, add mods, or adjust balance. This is exciting if you like new content, but disruptive if you run a public server where players expect consistency.
For a community server with a wipe schedule (start fresh every few months), ATM10 is fine. For a long-running world that you want to be stable for a year, ATM9 is the safer choice.
JVM Optimization
ATM10 on Java 21 opens up Generational ZGC, which is the best garbage collector for large heaps:
java -Xms10G -Xmx10G -XX:+UseZGC -XX:+ZGenerational -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -jar server.jar
ATM9 on Java 17 is best served by G1GC with Aikar's flags (the traditional recommendation).
This matters because ZGC eliminates the micro-stutters that G1GC sometimes causes during garbage collection. On ATM10, this translates to smoother chunk loading and more consistent TPS. It is one of the less visible but most impactful advantages of running the newer pack.
Progression and Content
Both packs use a quest book to guide progression. The general flow is similar:
- Basic survival and base building
- Early tech (Create, basic power generation)
- Mid-tier automation (AE2, Mekanism processing)
- Advanced magic (Ars Nouveau, Botania)
- End-game (creative items, dimension exploration, ATM star)
ATM10's quest book is still being refined. ATM9's quest book has been polished over multiple updates and provides a smoother guided experience. If you are new to kitchen-sink modpacks, ATM9's quest book is a better teacher.
Which One Should You Choose
Choose ATM9 if:
- You want a fully stable, mature pack
- You are running a long-term server (6+ months without resets)
- A mod you need has not updated to NeoForge 1.21
- You are new to ATM and want the most polished guided experience
- Your server is already running ATM9 and players are mid-progression
Choose ATM10 if:
- You are starting a new world
- You want the latest mod versions and features
- You want better performance (Java 21 + NeoForge improvements)
- You do not mind occasional updates that change things
- You want to take advantage of Minecraft 1.21 world generation
The pragmatic answer for mid-2026: if you have no existing ATM world, start with ATM10. The performance is better, the mods are more current, and the pack will continue receiving content updates. If you are already invested in ATM9, there is no rush to migrate. Your world and your progression are worth more than marginal performance gains.
FAQ
Can I transfer an ATM9 world to ATM10? No. The packs target different Minecraft versions (1.20.1 vs 1.21) with different mod loaders (Forge vs NeoForge). World data, mod IDs, and block registries are incompatible. You need a fresh world for ATM10.
Is ATM10 harder than ATM9? The difficulty is comparable. Some recipes changed, some progression paths shifted, but the overall challenge level is similar. If you found ATM9 easy, ATM10 will feel the same.
Can I add mods to ATM10? Yes, but with caution. Adding mods to a kitchen-sink pack increases the chance of conflicts. Add one mod at a time, test, and back up your world before adding the next. Check the ATM Discord for known compatible additions.
How much RAM do I really need? For a server with 3 to 4 friends: 8 GB for ATM10, 10 GB for ATM9. If in doubt, start with 10 GB on either pack and monitor usage. If you consistently use over 80% of your allocation, upgrade.
Related guides: optimize your ATM server with ZGC vs G1GC comparison and ATM10 server optimization guide. For ATM10 specific setup, see server requirements and JVM arguments. Browse all recommended mods in best Minecraft mods 2026.
Which pack has more content? ATM9 currently has more mods (~400 vs ~350), but this gap is closing as mods update to NeoForge. Content depth (quests, progression, integration) is comparable.