UE5 not backward compatible with UE4.26 anymore


Initially, it was said that UE5 was backward compatible with UE4.26. I think I even tried it successfully.

Today, after a while, I have tried the same, and it’s not backward compatible with UE4.26 anymore. I think after the Early Access update.

PS: to check it, it’s as easy as creating any UE5 project, put a cube, for example, in the default map, save the map, close the project, and try to open it again with UE4.26 → the map is desappeared, so no compatible.

PLEASE, that was an important feature. Make it possible again, please.

Thank you and best regards!

I don’t think that was ever the case, I think what they meant is projects created in 4.26 can be opened in UE5, however once an asset is saved in UE5 you can’t open it back in an older version.

That’s not right, I think.

As stated on the FAQ section about UE5 (Frequently Asked Questions - Unreal Engine):

UE5 Early Access is backward-compatible with Unreal Engine 4.26 and you will be able to open your 4.26 projects in UE5 Early Access. At the time of releasing Unreal Engine 4.27, projects generated in it won’t be compatible with Early Access; however, it is our intention that 4.27 projects will be compatible with the UE5 full release.

Perhaps you’re right, however I do think that what they really meant is
backward-compatible is the ability to open a project created in 4.26 inside UE5

and you will be able to open your 4.26 projects in UE5 Early Access

I see your point. I was just editing the post to say:
(Or maybe yes, and “UE5 being backward compatible” simply means that “UE4 is forward compatible with UE5”, which, for me, seems like a poor and confusing way to express it).

I think in some video, or somewhere, I read or even listen something like: you can try your projects in UE5! but don’t worry, because if something goes wrong, yo will be able to reopen it in 4.26… but not sure now.

But thanks! As maybe you are right and you have given me the answer.

Maybe someone else can confirm. I agree that’s kind of confusing if it’s the case.

I haven’t tried it yet but if you open a project from 4.26 in UE5 for example as long as you do not save any asset you should be able to open it back in 4.26. Saving an asset with a different version is what makes it incompatible.

It’s like copying a folder from UE4 to UE5 and then copying it back to UE4, as long ast hose files aren’t changed they’re still the same file.

I’m pretty sure it was never possible, the versions didn’t change after EA1. I don’t think they ever change after a version is locked in.

1 Like

The definitive answer comes from an Engine Contributor
in another post.
UE 5.1 in GitHub ue5-main and backwards compatibility with 5.0 -

Unreal only implements forward migrations, so if you use the dev branch, you will not necessarily be able to open the project in a release branch for even the same version.

You should keep a backup of your original Project in a new separate directory.

When the question about UE5 conversion comes up always select “make a copy”. If convert in place you will possibly corrupt many assets.

The backward compatibility of any prior/older version is not supported, except by making a backup copy of the project and this applied right back to version UE 4.14

This is VERY disappointing, the main reason I kept on building in 4.26 was so that I could then move it to UE5 on release! I know it worked with preview but not on full release? I feel duped. I’ve been having trouble with Unity since 2019.3 the new UI and starter assets and no Remote 5 for android testing which made me move to UE and now this grrrr… WHAT IS GOING ON these last couple of years? No compatibility and loss of and sense of continuity.
Can I move my game to 4.27 from 4.26 then use UE5 on release? I’m still quite new to UE so be gentle lol Cheers guys

HI @P.A.Hughes,
I WONT advise moving to 4.27 to get to UE5. I have had many problems converting 4.27 projects.

Projects in 4.26 and earlier versions convert and work well, the source code changed so quickly that there was a period where conversion did not work, but this has been fixed with a new conversion code.

We in Unreal don’t understand Unity? The engines are completely different engines and cant be compared.

Make a backup and use the copy to convert to don’t convert in place, click convert and you will get a project with 5.0 ending in the file name.

Make sure you use a source code version, not the Early Access 2 BINARY version from the Epic Launcher.

Use the post Visual Studio 2022 builds and runs UE5.0 - Development Discussion

Assets saved in an older engine version can be opened in a newer engine version (if you save an asset in 4.26, it will open in 5.0, etc…)
Assets saved in a newer engine version cannot be opened in an older engine version (if you save an asset on 5.0 you can no longer open it in 4.26, etc…)

The 5.0 EA vs 4.27 thing is a bit confusing, but 5.0EA was branched off of the 5.0 development before 4.27 was finished, so it was sort of both an older build than 4.27 and a newer build than it, hence 4.27 <-> 5.0 EA not being compatible in either direction.

However, anything made in 4.26, 4.27, 5.0EA, or 5.0 proper (but not UE5 main after Release-5.0 was created, which is now 5.1) will open in the final release of 5.0.0, hopefully that helps clear things up.

Michael Noland


To make it even clearer:

  • Saved in 4.0 - 4.26 → Loads in any version the same or newer (note #1)
  • Saved in 4.27 → Loads in 4.27 or 5.0.0 or newer (but not 5.0EA)
  • Saved in 5.0EA → Loads in any version of UE5
  • Saved in 5.0.0 → Loads in 5.0.0 or newer (but not 5.0EA)

and in the future, the expectation would continue to be:

  • Saved in 5.1 → Loads in 5.1 or newer, etc… (note #2)

The 4.27 <-> 5.0EA issue is unfortunate and it makes everything harder to understand, but it was communicated in advance before either 4.27 or 5.0EA came out.

  1. The game API does change over time, so, e.g., Blueprints saved all the way back in 4.0 might call functions that were deprecated in 4.10 and no longer exist in 5.0, but they should still load and let you fix up the deprecated/removed references.

  2. At some point in the future we might raise the minimum asset compatibility version but if we do so we’d communicate it in advance and wouldn’t be bringing it all the way up to the previous version (e.g., hypothetically we might say projects older than 4.20 need to be resaved anywhere between 4.20 and 5.2 before moving to 5.3 or something like that, but for now we attempt to provide loading compatibility for content saved all the way back in a private beta of UE4 before 4.0 was released.

Michael Noland


In the latest UE5 Preview 2 BINARY, versions 4.27 projects ALL convert successfully, which is a great improvement over the EA version.