topic Re: Fusion no longer starts instances once the program is opened in Fusion Support Forum

Fusion no longer starts instances once the program is opened

cad2015XYT3X — Sun, 31 Aug 2025 16:53:13 GMT

I use Fusion on several PCs, which normally isn’t a problem. For example, when I open a .step file, Fusion starts and the file loads just fine. If I then open another .step file from Explorer on my old PC, Fusion correctly opens a new tab/window inside the application and displays the file. That’s how Fusion is supposed to work now, since running multiple instances is no longer possible as it used to be. So far, no problem.

Now to the actual issue: On my new work PC, where I did a completely fresh installation of both Windows and Fusion, this no longer works. I can still start Fusion by opening a .step file, but as soon as I try to open another .step file—where Fusion should open it in a new tab/window—it doesn’t happen.

This is definitely a Fusion issue. On my old PC, where Fusion was always updated on top of the existing installation, it still works as expected. But on the new PC with a clean Windows and Fusion installation, it doesn’t. It’s not hardware-related either—even if I reset the PC back to a previous state where it worked, a clean reinstall breaks it again. So Autodesk must have changed something that prevents this behavior after a fresh installation.

Does anyone know a solution? Probably this will be fixed in a future update anyway, but right now the only workaround is to open .step files directly from within Fusion—which is not really the point. So I’m hoping for suggestions, or do I just have to wait until Autodesk fixes it?

Re: Fusion no longer starts instances once the program is opened

dsouzasujay — Mon, 01 Sep 2025 03:42:17 GMT

Hi @cad2015XYT3X ,

Can you please provide a video of the process?

Re: Fusion no longer starts instances once the program is opened

cad2015XYT3X — Mon, 01 Sep 2025 15:57:46 GMT

(view in My Videos)

Here are two videos I recorded with the Snipping Tool to better illustrate the problem.
Video 1 shows Fusion on an older PC where it was only updated,
and Video 2 shows Fusion on a freshly set up Windows installation.

Betreff: Fusion no longer starts instances once the program is opened

cad2015XYT3X — Tue, 13 Jan 2026 15:16:13 GMT

Resolved.

I noticed today that Fusion finally fixed the issue after what feels like half a year. I can now use Fusion properly again.

Betreff: Fusion no longer starts instances once the program is opened

TrippyLighting — Thu, 15 Jan 2026 15:39:21 GMT

Running more than one instance of Fusion concurrently is not a recommended practice, or has it ever been.

As such I doubt there was an intentional "fix".

Betreff: Fusion no longer starts instances once the program is opened

cad2015XYT3X — Thu, 15 Jan 2026 17:53:52 GMT

Sorry, but I have to disagree.

Previously, you could open multiple windows in Fusion, which definitely had its advantages. At some point, this was changed, and tabs were introduced instead. Since then, new projects are started in the already open Fusion window, just like in Internet Explorer.

Why wouldn't that be the intended behavior? Are you really only supposed to have one project open at a time? That doesn't make sense to me, no offense intended.

Incidentally, on older computers where Fusion has been installed for years, this works perfectly fine everywhere. Presumably, the old structure is still there. The problems only occur on new computers or with a fresh Windows installation.

Basically, every CAD/CAM program does this: either it opens a new window (e.g., Hypermill and Fusion used to do this), or it opens a new tab in the existing window. This is standard practice.

The only real problem with Fusion is that if it crashes, all open tabs are lost. That's its only drawback.

Betreff: Fusion no longer starts instances once the program is opened

TrippyLighting — Thu, 15 Jan 2026 18:27:19 GMT

@cad2015XYT3X wrote:

Sorry, but I have to disagree.

With what?

I did not say that it cannot be useful. That is irrelevant! I use it myself occasionally.

I said that it is not a recommended workflow for technical reasons.

That is based on feedback I've received directly from members of the Fusion Dev team!