[Isaac Sim 5.1][Windows][pip] STEP import fails because HOOPS subprocess cannot find kit\python

[tejas.murkute]

Important: Isaac Sim support

Isaac Sim Version

6.0.1
6.0.0
5.1.0
5.0.0
4.5.0
4.2.0
4.1.0
4.0.0
4.5.0
2023.1.1
2023.1.0-hotfix.1
Other (please specify):

Operating System

Ubuntu 24.04
Ubuntu 22.04
Ubuntu 20.04
Windows 11
Windows 10
Other (please specify):

GPU Information

• Model: NVIDIA GeForce RTX 5070 Laptop GPU
• Driver Version: 592.15

Topic Description

Failing installation:

• Isaac Sim installed using pip in an isolated Python 3.11 environment
• Python: 3.11.15
• isaacsim: 5.1.0.0
• isaacsim-core: 5.1.0.0
• isaacsim-extscache-kit: 5.1.0.0

Working comparison:

• Official Isaac Sim 5.1 standalone Windows ZIP installation

Converter extension versions in the standalone installation:

• omni.kit.converter.cad: 205.0.0
• omni.kit.converter.hoops: 509.1.0
• omni.kit.converter.hoops_core: 509.1.0

The pip installation uses the same HOOPS converter version, 509.1.0.

Detailed description

Importing a STEP assembly using File > Import fails in the pip-installed
Isaac Sim 5.1 GUI.

The GUI only reports that the import failed. The main Isaac Sim console
and the terminal used to launch Isaac Sim do not show the underlying
error.

The CAD Converter launches a separate Kit subprocess. Its log shows that
the subprocess expects a bundled Python directory at:

/Lib/site-packages/isaacsim/kit/python

That directory is not present in the pip installation. The subprocess
therefore fails to initialize the Python scripting plugin before CAD
conversion begins.

I then installed the official standalone Isaac Sim 5.1 Windows ZIP and
repeated the import with the same STEP file and import settings.

In the standalone installation, the converter subprocess successfully
initialized Python and converted the STEP file to USD.

Steps to reproduce

1. Install the full Isaac Sim 5.1 pip distribution on Windows in a
   Python 3.11 environment.
2. Launch the Isaac Sim GUI.
3. Confirm that the CAD Converter and Asset Importer extensions are
   enabled.
4. Select File > Import.
5. Select a STEP file.
6. Select a local USD destination.
7. Leave the converter settings at their defaults.
8. Click Import.

Expected result

The STEP file should be converted to USD.

Actual result with the pip installation

The import fails before conversion.

The separate converter-process log contains:

Couldn’t set PYTHONHOME env var, path:
“/Lib/site-packages/isaacsim/kit/python”
isn’t an existing directory
(from config at:
“/plugins/carb.scripting-python.plugin/pythonHome”).

Failed to startup plugin carb.scripting-python.plugin
(interfaces: [carb::scripting::IScripting v1.0])
(impl: carb.scripting-python.plugin)

Standalone comparison

The same STEP file was imported using the official Isaac Sim 5.1
standalone Windows ZIP.

The standalone converter log reports:

Python interpreter was successfully initialized.

Starting File Conversion

File conversion is successful

The conversion completed in approximately 4.7 seconds and produced a
valid USD file.

The standalone installation contains its bundled kit/python directory,
whereas the pip installation does not.

Questions

1. Is the CAD/STEP Converter officially supported in the Windows pip
   distribution of Isaac Sim 5.1?
2. Is the absence of isaacsim/kit/python expected in the pip packages?
3. Is there a supported way for the converter subprocess to use the
   active Python environment rather than expecting bundled Python?
4. If STEP conversion requires the standalone installation, could this
   limitation be documented in the pip installation or CAD Converter
   documentation?

Related reports

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Relevant log excerpts

Pip installation — failed converter subprocess

2026-07-29T09:01:07Z [5ms] [Error] [carb.scripting-python.plugin]
Couldn't set PYTHONHOME env var, path:
"<python-environment>/Lib/site-packages/isaacsim/kit/python"
isn't an existing directory
(from config at: "/plugins/carb.scripting-python.plugin/pythonHome").

2026-07-29T09:01:07Z [6ms] [Warning] [carb]
Failed to startup plugin carb.scripting-python.plugin
(interfaces: [carb::scripting::IScripting v1.0])
(impl: carb.scripting-python.plugin)

2026-07-29T10:37:33Z [30ms] [Info] [carb.scripting-python.plugin]
Python interpreter was successfully initialized.

2026-07-29T10:37:33Z [42ms] [Info] [omni.ext.plugin]
[ext: omni.kit.converter.cad-205.0.0] registered

2026-07-29T10:37:33Z [42ms] [Info] [omni.ext.plugin]
[ext: omni.kit.converter.hoops_core-509.1.0] registered

2026-07-29T10:37:33Z [642ms] [Info] [main]
Starting File Conversion

2026-07-29T10:37:37Z [4,697ms] [Info] [main]
File conversion is successful

[lhuang]

Hi @tejas.murkute,

Thank you for the detailed investigation and for comparing the pip installation with the standalone package. Your diagnosis is correct: the HOOPS converter starts a separate Kit process that expects the bundled kit/python runtime. That runtime layout is present in the standalone installation but is not provided by the Isaac Sim 5.1 pip packages.

CAD/STEP conversion through this extension is therefore not supported from the Isaac Sim 5.1 pip environment. There is currently no supported configuration for redirecting the converter subprocess to the active virtual-environment Python. Copying or symlinking the standalone kit/python directory into the pip installation is also not recommended, because the Kit runtime and its packaged dependencies must remain version-aligned.

The supported workaround is to perform the STEP-to-USD conversion using the standalone Isaac Sim application, then use the generated USD in your pip-based workflow.

We agree that this limitation should be clearer in the pip installation and CAD Converter documentation, and we will pass that feedback to the documentation team. Please also note that Isaac Sim 5.1 is now an unsupported release, so we recommend using the current supported release where possible.

Thanks again for providing a clear reproducer and the converter-process logs.

[lhuang]

Closing since there is no update for 2 weeks. Feel free to re-open or open a new issue if you still need any support.