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.

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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