Chartlets is currently restricted to Python <3.13. This was due to Vega Altair not supporting it back in Oct 2024. But in Nov 24, 2024, Python 3.13 support was added. Although we use the latest Altair version 5.5.0 which supports Python 3.13 https://github.com/vega/altair/releases, we did not remove the Python version limitation.