I searched and I may have misremembered, the free version seems to have been around since the start except that the free version was initially invite and desktop only. Eventually everyone could use it but still only on desktop. The free version was even more limited back then it seems with a limit on how many hours you could listen to each month.

I could personally never use it. Because it was so incredibly limited. Not being allowed to skip tracks makes it unusable and I’m genuinely surprised anyone used it apart from trying the service.

I have a faint memory of it being announced that Spotify first got a free tier but I may be completely wrong, I was very young back then. I’m also from Sweden so we had Spotify very early compared to most countries and it got popular very quickly here.