I recently passed 40,000 but my Substack is free so it's not a revenue source for me. I haven't really looked at who they are - at some point it would be interesting to export the CSV of the subscribers and count by domains, I guess.

My content revenue comes from ads on my blog via https://www.ethicalads.io/ - rarely more than $1,000 in a given month - and sponsors on GitHub: https://github.com/sponsors/simonw - which is adding up to quite good money now. Those people get my sponsors-only monthly newsletter which looks like this: https://gist.github.com/simonw/13e595a236218afce002e9aeafd75... - it's effectively the edited highlights from my blog because a lot of people are too busy to read everything I put out there!

I try to keep my disclosures updated on the about page of my blog: https://simonwillison.net/about/#disclosures