Add support for free-threaded python

[rrad5409]

Describe the bug

I've been using rerun in one of my projects for quite a while now, and it's been working perfectly fine. We've hit some pretty intense compute bottlenecks, and we're now switching to using free-threaded python to bypass the GIL. Python itself and pip are working just fine:

$ python -VV
Python 3.14.2 free-threading build (main, Dec  9 2025, 19:03:17) [Clang 21.1.4 ]
$ pip -VV
pip 25.3 from XXX/.venv/lib/python3.14t/site-packages/pip (python 3.14)

But for some reason I cannot pip install rerun-sdk, as it's just not finding the package. Note that this works perfectly fine if I use normal python 3.14, but using 3.14t breaks. It's definitely not a versioning issue, as I'm also using the same versions of everything.

$ pip install rerun-sdk
ERROR: Could not find a version that satisfies the requirement rerun-sdk (from versions: none)
ERROR: No matching distribution found for rerun-sdk

# this is the commit for 0.27.3
$ pip install --pre --no-index -f https://build.rerun.io/commit/3bddb14/wheels rerun-sdk
Looking in links: https://build.rerun.io/commit/3bddb14/wheels
ERROR: Could not find a version that satisfies the requirement rerun-sdk (from versions: none)
ERROR: No matching distribution found for rerun-sdk

To Reproduce

1. Install free-threaded python.
2. Attempt to pip install the SDK, either using the package name, or from the wheels.

Expected behavior

The package gets installed.

Screenshots

N/A

Backtrace

N/A

Desktop (please complete the following information):

• OS: Ubuntu 25.04
• Arch: x64
• Rerun: Rerun 0.27.X, but probably more.

Original Post

https://discord.com/channels/1062300748202921994/1451075642824069251

Additional context

To me it looks like a compatibility issue, where the wheels that are being built aren't compatible with CPython. This might be because of the ABI - your releases are for -abi3 where my python only supports -none, or it could be because you are targeting python 3.10 not 3.14.

Similar Issues

• Error when installing rerun-sdk using python on Jetson Orin with Ubuntu20.04 LTS #9194
• rerun_py/build.rs leads to error in nixpkgs packaging #7411
• Cannot install using pip on Ubuntu 20.04 #1320
• Proper free-threaded ABI support blockers python-cffi/cffi#126
• Add support for the free-threaded build python-cffi/cffi#178
• Add support for free threaded python apache/datafusion-python#1324
• pep 803

[rrad5409]

I had a look at the PyO3 free-threading docs, which mentioned usages of unsafe and 'py lifetimes. I have zero understanding of how rerun works under the hood, so apologies if the following is completely wrong.

For unsafe, all of it was inside the core rerun crates, and I don't think will be affected at all by this:

• buffer casting/indexing
• allocations
• accessing environment variables
• de/serialisation
• FFI calls to C

For 'py lifetimes, they all seem to be immutable buffer reads, which I think are fine. However, in catalog.table_entry.rs, there are a few usages of PyRefMut, and that's all I could find.

[rrad5409]

According to @ntjohnson1 there might be some considerations as to whether the dependencies support free-threading. I used https://py-free-threading.github.io/tracking/ and https://hugovk.github.io/free-threaded-wheels/ to validate the python deps from pyproject.toml and pixi.toml. I ignored ones I know are not python, like clang and ffmpeg, and build tools like setuptools:

Free-Threaded Wheels:

• numpy
• pyarrow
• pillow
• attrs

No free threaded support:

• datafusion

[ntjohnson1]

A few small updates:

• Removed the bug label since this is a feature request rather than a bug
• I updated your list since we only require the packages in pyproject to be supported. Everything else in pixi is for our convenience but what gets released to pypi should be withing the pyproject
• Opened the issue on datafusion because that is our only (but fairly large/central) dependency that doesn't yet support free threading

Beyond just `py lifetimes it also calls our knowing that your code is already thread safe. One approach to this is marking classes as frozen and managing mutability with rust in our wrappers which all live at https://github.com/rerun-io/rerun/tree/main/rerun_py/src. I'd have to dig deeper if there are other nice rust/pyo3 patterns that support this.