Linux

Incorrect, redhat are simply saying that to get any source you have to have a centos stream subscription, which would be correct as if you have centos stream binaries you need a subscription anyway, so basically you only get the centos stream source on request if you actually happened to be a centos stream customer.

Now, what happens to centos stream users who used to be subscribing, well they should still be able to get the source for a reasonable fee (to cover distribution costs) for the binary code they have to hand. That means that if they are on an old centos and they want the source for project X version 2.3, and project X v2.3 is under a copyleft license, legally RedHat have a requirement to provide it upon request, but they have no legal requirements to provide source for a version that is from a later version of centos if the customer doesn't actually have the binaries.

So if they can somehow keep future binary versions of centos code out of the hands of non-paying users they don't have to give source to versions they don't have. I don't think they can do that easily.

This is only for copyleft code. This only applies to code they applied (note I didn't say contributed) to copyleft code. Thus if they modified GNU Grep, their modifications are under the GPL, thus the code must be provided to anyone who asks for it if they have the binary. But if it is code unique to centos or applied to a project that isn't under a copyleft licence, or is a project under a copyleft licence that allows non-copyleft modules or linking etc, they don't have to give any of that.

The GPL is pretty simple, I used to read V2 as a kid in the 90's and saw it like a Bible lol. V3 is more thorough and not as nice a read but it's still very clear. However, not all software in a Linux distribution is protected by a copyleft licence like the GPL, this is the line that separates Free Software from Open Source. Welcome to the big problem of Open Source. You all want source code? Well Free Software gives you the rights for it and uses copyright law to protect those rights. But Open Source came about because that idea was incompatible with business who wanted the opposite. So you should expect Redhat to honour their legal obligations under the GPL but you won't get a source version of centos as not everything in centos is GPL, some will be MIT, or Apache or BSD, and they are not copyleft licences and they give you no right to the source code at all.

Seems to me that a lot of people need to brush up on their Free Software, Richard Stallman, FSF, GNU, Open Source history. Free Software is Open Source as defined by the OSI (you don't know who they are? Brush up like I said) but much that is Open Source is not Free Software and even more is not copyleft.

If you think that copyleft ideology applies to anything considered as "Open Source", well you don't have a clue what anything is actually about and you need to do some reading and listening of some Richard Stallman speeches because this confusion is precisely what he and the FSF have been combatting for years only to get barely anywhere because of how marketable "Open Source" is.

So again remember, not all of centos is copyleft. What is copylefted is protected but you won't get a buildable source version of Centos unless you are a subscriber as many of its parts are not legally available to you, you can get all the GPL copyleft code and centos specific modifications, but a working OS you won't get.