If you've scrolled through the Valheim 1.0 patch notes looking for the bit that affects your server, you'll have noticed the problem. It's a very long list of Nord Greatswords, Thunderblood Knucklechains and a small cookbook of oat recipes, and the handful of lines a server owner actually needs are sitting in among them, one bullet each, with no fanfare. Then two days later the 1.0.12 hotfix landed with a few more that matter just as much.
So I've been through both sets of notes line by line, and checked them against what 1.0 has actually done on the Valheim servers we run. What follows is only the stuff that changes something for a dedicated server. The new weapons can wait. For the launch-day picture (consoles, crossplay, what happens to an old world) we covered that in Valheim 1.0: What Changes for Dedicated Servers, so I won't repeat it here.
Which build you should be on, and why a restart won't get you there
Iron Gate's 1.0 notes never say which build number launch day actually was. The server does, though. On launch day, 9 September, our dedicated servers came up logging Valheim version: 1.0.7 (network version 39). On 11 September Iron Gate posted "Hotfix 1.0.10 & 1.0.12", and the server build that went out with it logs Valheim version: 1.0.12 (network version 40).
That network version change is the part to pay attention to. We haven't sat and watched a failed join to prove it, but a client and server on different network versions is exactly the mismatch Valheim bounces people for, so I'd treat a server still on 1.0.7 as unjoinable for anyone whose Steam client has updated. If a few of your players have been getting kicked back to the menu since the hotfix, that's the first thing I'd check.
Heads up: restarting your server doesn't update it. It's an easy assumption to make, and at least one server we checked had been restarted a full day after the hotfix and was still sitting on 1.0.7. On our current panel, press Update on your server (or add an Update scheduled task so the next one happens on its own). On the older control.low.ms panel it's Steam Update. Our update guide has the full order of operations if you want it.
The Switch 2 exception
There's one group who might deliberately want the older build. The 1.0.12 fixes are Steam only for now, and Iron Gate's hotfix post added this afterwards: "Due to an unforeseen issue, the patch was unable to be uploaded to Switch 2. Unfortunately this means crossplay is not currently supported between Switch 2 and other platforms."
Their workaround is to put the Steam game and the dedicated server on the default_old branch, which is the 1.0.7 launch build. Two catches, both from the same post. You lose every fix in 1.0.12, and "there is no work-around for playing crossplay between the Playstation 5 & XBox and Switch 2 at this moment". As we read it, your Steam players would need to switch branch too, because otherwise you're back to the version mismatch above. So only do this if Switch 2 players are the ones you can't do without. If that's you, open a ticket and we'll sort the branch out with you, and put it back once Iron Gate get the patch onto Switch 2.
The new save system shipped
This is the big one, and it gets a single line in the 1.0 notes:
"New save system: Splits world data across chunks to reduce how much data is serialized and written to improve performance, and is designed to be resilient against mid-write failures"
That's the system from the May public test build, and yes, it made it into 1.0. On disk a world is no longer a .db and a .fwl sat side by side. It's a folder named after the world, full of small .chunk files plus a few _main files, and only the chunks that changed get rewritten on each save. Valheim's own auto-backups are folders now as well.
Existing worlds convert themselves the first time a 1.0 server loads them, and you don't need to do anything. What we saw on converted servers was the old pair renamed to .db.old and .fwl.old, a separate _backup_ copy of the pre-conversion world with a timestamp in its name, and then the new folder. Your old flat auto-backups are left alone. It's a careful migration, honestly, and the converted worlds we looked at came through it intact.
What changes for you is the unit you handle. If you download, upload or restore a world by hand, it's the whole folder now, never a pair of files. And that _backup_ copy is the world as it was just before its first 1.0 load, so picking it by accident rolls you back to that moment. Our save location guide covers the upload side.
Note: on our current panel, the World Name suggestions and the New World tool were built around the old two-file layout and don't handle 1.0 world folders properly yet. Fixes are on the way. Until then I wouldn't lean on either for a 1.0 world, and if you want a fresh world, open a ticket and we'll set it up with you.
The launch arguments for built-in backups (-backups, -backupshort, -backuplong) still work exactly as before. Our logs also show a new guard where saving is blocked if the disk is nearly out of space, which isn't in the notes but is a sensible thing to have.
Ban lists and whitelists were half broken on 1.0.7
1.0 brought in a new player ID format, and the hotfix admits what that did to the lists you keep on the server:
"Fixed a problem with banlist and whitelist that made them only compatible with new IDs (e.g. V_123456789) even though they should work with old IDs too (e.g. Steam_123456789)"
Read that the other way round and it means on 1.0.7, the old-style entries in bannedlist.txt and permittedlist.txt weren't doing their job. If someone you'd banned turned up between launch and the hotfix, or a whitelisted friend couldn't get in, that's why. Updating to 1.0.12 fixes it, and your existing entries don't need rewriting. For mixed Steam and console lists, our crossplay guide goes through the platform-prefixed IDs you'll see in the log.
Don't touch the item stands without a backup
This one's easy to miss because it's buried in brackets. The 1.0.12 fix reads:
"Items on armour stands and item stands no longer lose their durability & upgrade level IF the world has not yet been loaded in the 1.0 update (We are however looking into a better fix for this so do not remove high level items (fish, weapons, armour, etc) from your item stands without using backups if you have been playing 1.0!)"
So the fix only fully covers worlds that hadn't been loaded on 1.0 yet. Any world that was running between launch and the hotfix has been. I'd tell your players plainly: nobody takes their good gear off a stand until you've taken a backup. It's one button in the panel, and it's the difference between an annoying afternoon and a very angry Discord.
A crash fix that matters for uptime
One line, easy to skim past: "Fixed a crash that could trigger when players tried to access a zone that wasn't loaded". The notes don't say whether that was the client or the server falling over, but on a world with players spread across the map it's the sort of thing you'd hit, so it's another reason not to sit on 1.0.7.
Mods, achievements and the Unity upgrade
The 1.0 notes say "Unity engine upgraded" and nothing more. For what it's worth, a pre-1.0 BepInEx log on one of our servers reports Unity 6000.0.61 and a 1.0 server logs 6000.0.75f1. Between that and the new save format, I wouldn't assume a mod written for 0.221 still loads. Iron Gate's 1.0 FAQ was blunt about it: "we cannot guarantee that any mods will be functional when 1.0 releases". Anything that reads or writes world files directly needs a 1.0 update before I'd let it near a world. Our mods after 1.0 guide is the place to start.
On achievements, the FAQ says most devcommands put a flag on your character and world that permanently locks you out of them. 1.0.12 softens that: "Achievements can be now be opted into even if you have used devcommands or mods by the new devcommand". Whether you use it is between you and Odin.
The smaller lines, and what isn't there
A few more worth knowing, including one thing the notes leave out entirely:
- There are no new or changed dedicated server launch arguments in either set of notes. The new devcommands (
findbiome,biomeinfo,altbiomesand friends) are console commands, not startup flags. Thestart_headless_server.batthat ships with 1.0.12 still uses-crossplay. - The player cap hasn't moved. Iron Gate's FAQ calls 1.0 "a game for 1-10 players".
- World generation is "much faster" and terrain changes use less network traffic, according to the notes. There are also "some IPv6-related bugs" fixed, without detail.
- The alternate biomes at the "outer edges of Valheim" only turn up properly in ground nobody has explored yet. Deep North on an existing world explains why your north still looks the same.
That's everything in two patches' worth of notes that I think a server owner needs. If your server's still on 1.0.7, if you need default_old for Switch 2 friends, or you want a fresh 1.0 world set up, open a ticket and we'll sort it with you. And if you're starting a new world for 1.0 from scratch, the Valheim hosting page is the quick way in.