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I read this a few years ago.

Time Exclusive: OpenAI Used Kenyan Workers on Less Than $2 Per Hour to Make ChatGPT Less Toxic

https://time.com/6247678/openai-chatgpt-kenya-workers/

Beyond that, I think the reason you haven't heard more about it is that it happens in developing countries, so western media doesn't care much, and also because big AI companies work hard to distance themselves from it. They'll never be the ones directly employing these AI sweatshop works, it's all contracted out.

Good article from 2023, not much data though if that's what you're looking for:

https://nymag.com/intelligencer/article/ai-artificial-intell...

unwalled: https://archive.ph/Z6t35

Generally seems similar today just on a bigger Scale. And much more focus on coding

Here in the US DataAnnotation seems to be the most marketed company offering these jobs

This is not going to be as deep/specific as you want but a starting point from one of the companies that handles this sort of work is here: https://humandata.mercor.com/mercors-approach/black-box-vs-o...