[DONE] Verse VM test—Friday, October 23rd, 8am-12pm ET

General Announcements
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1

On Friday, October 23rd, we’re testing a new virtual machine (VM) for the Verse programming language on all Public and Private UEFN sessions. The test will run from 8am–12pm ET.

2026-10-23T12:00:00Z→2026-10-23T16:00:00Z

What should I expect?
During the test, users loading into a UEFN session (live) private and public sessions will be on the New VM.

What’s New compared to the last test?
In 42.40, Creators are able to toggle between the New and Old VM in a UEFN development and Live Edit session by:

  1. Selecting the three dot menu next to the Launch Session button

2026-10-19 13_36_44-NVIDIA GeForce Overlay DT
2026-10-19 13_36_44-NVIDIA GeForce Overlay DT524×143 8.11 KB

  1. Enable the Use Verse VM option

2026-10-19 13_37_59-
2026-10-19 13_37_59-620×459 97.4 KB

Hit something you think is related to the VM test?
Submit a report in this thread and include the following information:

  • Did this happen before the test window? If so, when?

  • Which island code are you seeing it on?

  • Steps to reproduce

  • How often does it happen: 10/10 times, or 1/10?

We’ll collect these and prioritize fixes internally before the next test.

2

The testing window is being extended to 3:00pm EST.

2 Likes
3

I was having issue when calculating private version for my map 6883-6554-3354 it was making me leave the the game to lobby then showed me connection error

4

The testing window has concluded, servers will be rolling over to the old VM after you join a new session.

5

Thanks for the info! We have this tracked for investigation!

6

We had a major game breaking bug that we received the first report for at 5:37AM PST (8:37 EST) which corrupted dozens our user persistent data that we couldn’t explain. We did a hotfix to our game last night and I thought it was related to that, but nothing we could see in code could explain it.

FWIW this is our map: https://fortnite.gg/island/9621-3035-2804

We had to unpublish our game, make a hotfix and have since published the change and things are mostly back to normal. That said, there are several other bugs that are now present that were not like that before (e.g. NPCs walking backwards).

The critical bug seems to have been due to a difference in how the Verse language was compiled and interpreted, and we had to make a change to code to accommodate. Is it possible the new VMs treat Verse code differently? We couldn’t explain why the bug occurred, so seeing this makes me think it might be related.

7

Hey. While testing the new Verse VM in edit sessions, we’ve encountered an issue with cancellation and defer.

The old Verse VM has a bug involving the following pattern:

Foo()<suspends> : void =
    defer. Print("Defer")
    race:
        # Expressions

If Foo is cancelled while the race is running, "Defer" is not printed. We’ve been using the following workaround:

Foo()<suspends> : void =
    branch:
        defer. Print("Defer")
        Sleep(Inf)
    race:
        # Expressions

With this workaround, "Defer" is printed whether Foo completes normally or is cancelled.

However, the workaround no longer works in the new Verse VM. This caused some issues in our island 4388-4237-1339. Although we have no evidence that public sessions have been affected, the issue is consistently reproducible in edit sessions.

8

Following up on my post above, the issue we saw in a nutshell…

?int := false doesn’t resolve to the same key in a map as ?int := option{0 > 10}

Whereas before it did.