Was it ever Apple who charged for tethering? I always thought it was in the hands of the networks and their various plans. Today it seems like it's not even a feature anymore, just something you can do with your phone (or, at least for me it is: I'm on one of the cheapest cellphone plans in my country and tethering just works)

In the US tethering is fundamentally different (or at least the carriers want you to think that so they can upcharge it)

Yes, it is the networks that demand extra payment for tethering. That is still a thing in the US; you have to pay extra for a plan that includes tethering.

Surprising from a European perspective. I have used tethering since before phones had a HTTP/HTML browser (~ 2001, remember WAP?). The question has always been do you have packet data or not, what is your bandwidth and volume. Nothing else is the operator's business.

Not really. They still separate on-device use from modem use. At least Bouygues Telecom in France does.

See my other comment: https://news.ycombinator.com/item?id=25243710

hors modem, you are right. So France is different. I'm 100% sure that has never existed in Finland (well, the most common packages are unlimited anyway) and 90% sure it's not common in Germany either (they use throttling after you reach the limit)

So technically, how do they differentiate the traffic?

Most of the time, tethering is allowed in the base package. What happens afterwards depends. They can either cut you off or throttle. The only experience I have with this is Orange, and they throttle to the point where you basically have no connection (SSH is unusable).

Not sure though how they differentiate the traffic. There are "access points" set up which I presume are used for either connection. In my case they are the same but I seem to remember on an older phone they used to be different. It was also a different provider. I'm also not sure how they would detect that they're changed.

Screenshot of my setup: https://imgur.com/a/xH88Itp

Tethering and hotspot traffic is still marked with a different APN type ("dun").

Does APN type go out over the network?

I thought that's an Android internal thing to decide which of several APNs to use.

Also the first 2 references that Google returns say dun is obsolete and not in use with today's devices. I believe that belongs to the ATD *99# era

(Havent't worked in the field for 10+ years, could be wrong.)

No it doesn't go out, but the APN itself does go out on the network and can be used to apply different billing to tethered vs mobile browser data usage. https://news.ycombinator.com/item?id=25244052 for more info.

The networks demand it, but Apple provided them the ability to demand it.