> From April 24 onward, interaction data—specifically inputs, outputs, code snippets, and associated context—from Copilot Free, Pro, and Pro+ users will be used to train and improve our AI models unless they opt out. [...]

> This program does not use:

> Content from your issues, discussions, or private repositories at rest. We use the phrase “at rest” deliberately because Copilot does process code from private repositories when you are actively using Copilot. This interaction data is required to run the service and could be used for model training unless you opt out.

So yes, pieces of your private code can end up in training data if you're using Copilot with it and don't opt out.

The Reddit comment said "your private repo context will be used to train their AI models by default" which is an inaccurate summary.