All the Mods 9 vs 10: which to run on a server

For a new group server in 2026, pick All the Mods 10 unless you have a specific reason not to. It runs on NeoForge for Minecraft 1.21.1 with Java 21, it is the pack the All the Mods team is actively developing, and it has the newer vanilla content. All the Mods 9 runs on Forge for Minecraft 1.20.1 with Java 17, and it is the right choice in three cases: your group already has an ATM9 world worth keeping, a mod you care about only exists in the 1.20.1 version, or your players want a pack whose quest line and balance have had years to settle. The hardware cost is similar - both want an 8 GB heap as a floor and more for a busy group - with ATM10 a little heavier because it carries more mods. And there is no upgrade path between them: an ATM9 world does not become an ATM10 world, so the choice you make on day one is the one you live with.

The practical side of running either pack - server files, start scripts, chunk loading, pre-generation, updating without losing the world - is in the All the Mods server guide. This post is about choosing between the two, and about the parts of an ATM9 setup that differ from ATM10.

The two packs side by side#

Both are "kitchen sink" packs: a very large collection of tech, magic, exploration and storage mods, tied together by a quest book and an end-game item, the ATM Star, that needs a bit of nearly everything. The skeleton is the same. The base underneath is not.

Mod counts move with every release and are only a rough guide; the pack's CurseForge page shows the current list for each version. The loader version is pinned by each pack release too. Use the version the server files install and never upgrade Forge or NeoForge on its own.

Both packs have side variants worth knowing about when you choose:

• To the Sky - a skyblock version of each pack (ATM9 To the Sky, ATM10 To the Sky). World generation is close to free, so these run noticeably lighter. See skyblock server setup for the general approach.
• Lighter cuts - ATM9 has a "No Frills" variant and ATM10 has a "Lite" variant, both trimming the mod list. If your hardware is tight or your group finds the full pack overwhelming, look at these before cutting mods yourself.

Everything below is about the main packs, but the same reasoning applies to the variants.

What actually changes in play#

Most of the mods your group has heard of are in both: Create, Applied Energistics 2, Mekanism, Botania, Ars Nouveau, Twilight Forest, the Allthemodium ores and dimensions, and the usual storage and utility mods. A player who knew ATM9 will recognise most of ATM10 within an hour. The differences that matter are smaller and more specific.

Vanilla content

ATM10 sits on 1.21.1, so it has everything Mojang added between 1.20.1 and 1.21: trial chambers and the trial spawner, the breeze and the bogged, the mace, the crafter block, armadillos and wolf armour. ATM9 on 1.20.1 has cherry groves, archaeology, the sniffer and camels, but none of the 1.21 content. For a group that plays modded mostly for the mods this is a minor point. For a group that wants the newest vanilla structures to explore, it settles the question.

Mod versions and availability

Not every mod made the jump to NeoForge 1.21.1, and some mods changed substantially when they did. A few practical consequences:

• A favourite niche mod may be 1.20.1 only. If one player's whole reason for joining is a specific mod, check that it is in the ATM10 list before you commit. Adding a 1.20.1 Forge mod to a 1.21.1 NeoForge pack is not possible.
• Recipes and progression were reworked. ATM10's quest book and ATM Star recipe are not a copy of ATM9's. Players who finished ATM9 should expect a familiar shape with different details.
• Mod behaviour on the newer version can differ. Machines that were lag-free in one version can be heavier in the other, and the reverse. There is no general rule, which is why profiling on your own server (covered below) beats any forum claim.

Maturity

ATM9 has had a long run. Most of its crash bugs and balance problems were found and fixed by the thousands of servers that ran it, and its quest line is complete. ATM10 has been the main pack for a while now and is stable for normal play, but it still receives mod updates and changes more often - which is both the benefit (fixes and new content) and the cost (more frequent updates to manage on a server).

RAM and CPU cost#

The two packs cost about the same to host. ATM10 is somewhat heavier at startup and in memory because it loads more mods, and Java 21 does not change that much in either direction. The real driver of cost on both is the world, not the pack: how much has been generated, how many chunks are force-loaded, and what is running in them.

These figures hold for both packs. The ATM10 server files set -Xmx8G in user_jvm_args.txt; check what the ATM9 server files you download set, and raise it if it is lower than the table. The gap between heap and container is deliberate. Java uses memory outside the heap - metaspace for the classes of several hundred mods, thread stacks, buffers - and on packs this size that is one to two gigabytes. A heap set to the full plan gets the process killed from outside during chunk generation, with no crash report. How much RAM a Minecraft server needs has the arithmetic.

-Xms4G-Xmx10G

CPU is where both packs hurt. Minecraft runs each dimension's tick on one thread, and kitchen-sink packs put a lot of work in that tick: machines, pipes, block entities, mob farms. Clock speed matters more than core count, though a second and third core help with chunk generation, garbage collection and networking. As a rough guide, plan two fast cores for a small group and three or more for a busy server. CPU vs RAM for game servers explains how to tell which one you are short of before paying for more.

Startup time differs more than steady-state cost. ATM10 loads more mods and more recipes, so a cold start takes longer - several minutes on the first start, two or three afterwards on good hardware, with ATM9 usually a little quicker. That matters for scheduled restarts: a nightly restart on either pack means a few minutes of downtime, not a few seconds.

Disk is similar for both: the server files unpack to over a gigabyte, more after the loader installs its libraries, and a mature world with several explored dimensions runs to several gigabytes before backups. Plan generously.

Stability and updates#

Stability on a big modded server comes mostly from two things you control - leaving headroom on memory and not letting the world grow unbounded - and one you do not: how many bugs the pack version still has.

On that last point ATM9 has the edge. It has been played for a long time, its last releases changed little, and a server that is set up properly tends to stay up. The trade-off is that you get few new fixes; if you hit a bug in a mod's 1.20.1 version, it may never be patched.

ATM10 moves faster. Updates bring mod fixes and sometimes new mods, and they occasionally bring new problems. On a server that means:

• Do not update on release day. Wait a few days, read the issues players report, then update.
• Back up before every update and keep that backup until the new version has run cleanly for a week.
• Update server and players together. A client launcher that auto-updates before the server is the most common cause of "mod rejections" on join.

The update procedure itself - replace mods/, config/, defaultconfigs/ and kubejs/ from the new server files, keep world/ and your own settings - is the same for both packs and is laid out in the All the Mods server guide. When an update goes wrong, what to do when a mod update breaks is the recovery plan.

Which one to pick for your group#

Most groups can decide from one of these situations.

A new group, no existing world. ATM10. It is the current pack, it has the newer vanilla content, and your server will keep getting fixes for the life of the world.

You already have an ATM9 world. Stay on ATM9 for that world. The world cannot move to ATM10 (see the next section), and a long-running server's value is the builds in it. Start an ATM10 server alongside it if people want the new pack, but do not shut down a world your group is still playing.

Players who finished ATM9 and want something new. ATM10. The quests and the Star recipe are different enough to be a fresh run.

Small hardware budget. Either pack's lighter variant, or a To the Sky version. Cutting a full kitchen-sink pack down to fit a small plan rarely works well; the variants were built for exactly that.

A specific mod that only exists on 1.20.1. ATM9. Check before you decide, not after the world is a month old.

Players with weaker PCs. The client side matters too. Both packs want around 8 GB allocated to the game on a player's machine and a reasonably quick CPU. ATM10's extra mods make it a little heavier to load. If several players are on older laptops, a lighter variant is kinder to them than either main pack.

Whatever you pick, decide it as a group before the first start and write the exact pack version in your Discord. "ATM10" is not a version; "ATM10 5.2" is.

Why an ATM9 world cannot be upgraded to ATM10#

This is the question that comes up most, and the answer is simple: you cannot convert an ATM9 world into an ATM10 world in any way that keeps the modded content. Vanilla Minecraft upgrades worlds from 1.20.1 to 1.21.1 itself, but a modded world is mostly modded data, and that is where it breaks:

• Different loader. ATM9 runs Forge, ATM10 runs NeoForge. On 1.21.1 these are separate ecosystems; mods were rebuilt, and many changed how they store their data.
• Changed item storage. Minecraft 1.20.5 replaced item NBT with data components. Vanilla migrates its own items; mods have to handle their own, and in a pack of several hundred mods many do not migrate 1.20.1 data at all.
• Removed and renamed content. Blocks, items and entities that were renamed, merged or dropped between versions simply disappear when the world loads. Machines lose their contents, storage networks lose their items.
• New world generation. Chunks generated by ATM9 would sit next to ATM10 terrain with hard seams, and modded structures and ores would be wrong in every chunk already generated.

The All the Mods team does not support moving a world between major pack versions, and the honest summary is that the result, if it loads at all, is a world with broken bases. The same goes in reverse, and the same goes for any other pair of major modded versions - see Minecraft version upgrades for what vanilla and plugin servers can and cannot carry forward.

What you can carry over:

• Player memories and screenshots. Not a joke - the most common outcome is a final "last day" event on the old world, then a fresh start.
• Server settings. server.properties, whitelist.json, ops.json and banned-players.json use the same formats and can be copied across.
• Builds, with effort. A schematic tool can save a build's vanilla blocks and paste them into the new world. Modded blocks in the schematic will not survive unless the same mod with the same block exists in ATM10, and even then their contents usually do not.

ATM9 server setup basics#

Setting up ATM9 follows the same pattern as ATM10, with Forge in place of NeoForge and Java 17 in place of 21. The short version:

1. On the ATM9 CurseForge page, open the files list, pick the release your players will use, and download its server files from the additional files.
2. Unpack it into an empty server folder. You get mods/, config/, defaultconfigs/, kubejs/, a startserver.sh and startserver.bat, and user_jvm_args.txt.
3. Make sure the server runs Java 17. Forge for 1.20.1 targets it; running it on a different Java version is a common source of startup failures. JVM flags and Java versions shows how to check which one is in use.
4. Set the heap in user_jvm_args.txt to suit the table above.
5. Run the start script. On first run it installs Forge and its libraries, then starts the server. Accept the EULA in eula.txt and start again.
6. Wait through the first start; it generates configs and the world and takes several minutes.

$ unzip ServerFiles-<version>.zip -d /srv/atm9$ cd /srv/atm9$ java -version$ chmod +x startserver.sh$ ./startserver.sh

Two server.properties lines matter on ATM9 exactly as on ATM10:

allow-flight=truemax-tick-time=180000

allow-flight=true stops vanilla kicking players for flying with jetpacks and flight items. max-tick-time raises the watchdog from its default of 60 seconds so a heavy chunk generation does not kill the server. Use /forge tps on ATM9 (on ATM10 it is /neoforge tps) to see tick time per dimension. server.properties explained has the rest of the file, and NeoForge server setup covers how the ATM10 side installs if you are running both.

On RE:NODE the Minecraft line installs Paper by default, so either ATM pack is your own upload: there is no one-click modpack installer and nothing in the panel reads a CurseForge pack. The file manager unpacks the server files zip in place, the console shows the long first start unfiltered with memory and CPU graphs against your plan's limits, and the Startup tab is where the launch variables go. Backup slots on every plan are stored off the machine and restore with a button - which is what you want before every pack update.

Running both on one budget#

Some groups want to keep the ATM9 world alive while starting ATM10. Two kitchen-sink servers running side by side need two full sets of memory; there is no sharing between them. Options that do not double the bill:

• Archive the ATM9 world. Back it up, stop the server, and only start it for events.
• Run ATM9 on a smaller plan with fewer players. A world that only gets visited occasionally needs less CPU, though it still needs its 8 GB heap to load at all.
• Turn off force-loaded chunks on the old world. If nobody is playing it, nothing needs to tick while they are away. In FTB Chunks, force-loading can be limited per player in the server config.

The second server also needs its own port. Players connect to each by address and port, or by a hostname with an SRV record - see SRV records for Minecraft for giving each server a clean name.

FAQ#

Is ATM10 harder to run than ATM9?

Slightly. It loads more mods, so it starts more slowly and uses a bit more memory, but the difference is small next to what a mature world with many force-loaded bases costs on either pack. Plan the same plan size for both and let the world, not the pack, decide when you need more.

Can I use Java 21 for ATM9?

Forge for 1.20.1 targets Java 17, and that is what to use unless the pack's release notes say otherwise. Some setups run on newer Java, but when a 1.20.1 pack fails at startup with a class or module error, the wrong Java version is the first thing to rule out.

Can players on ATM9 join an ATM10 server?

No. The client and server must run the same pack at the same version. A player on ATM9 connecting to an ATM10 server is refused with a list of mismatched mods, and so is a player on a different ATM10 release.

Will ATM9 keep getting updates?

It has had a long run and its updates have slowed; ATM10 is where development is. Check the files page on CurseForge for the latest release date before planning a long server around ATM9, and expect fixes for 1.20.1-only bugs to be rare.

Should I wait for All the Mods 11 instead?

Only if your group would not start a world for months anyway. A new major pack takes a long time to settle, and early versions change often. A group that wants to play now is better served by ATM10 today than by an unfinished successor.