Presumably Stack Exchange isn't the only large website hosting user-contributed content which is using CC-by-SA licensing. It might be worth checking how other companies have handled this update.

Related: opensource.stackexchange.com/questions/7430/… . tl;dr cc-by-sa has a clause "You may Distribute or Publicly Perform an Adaptation only under the terms of:" "(ii) a later version of this License with the same License Elements as this License;"

@Sumurai8 IMO, the statements in the answer you link are flawed and not applicable to this situation. What "later version" appears to mean in CC BY-SA 3.0 is a later version of CC BY-SA 3.0. I see nothing that indicates that 4.0 is a "later" version of "this license" in that text. In fact, IMO, it's quite clear they are contemporaneous and 4.0 doesn't have the same "License Elements". If it was intended that 4.0 was "later", then that would be clearly indicated, at least by the Creative Commons, and there wouldn't be much of a distinction as to what a (continued)

"Creative Commons Compatible License" was between 3.0 and 4.0. In addition, you also are not taking into account the distinction between "Adaptation" and "Collection". What SE distributes is a "Collection", which is explicitly barred from being an "Adaptation". Thus the section which you are indicating is not applicable. As I mention in this answer, it is arguably applicable to individual posts which have been edited after the change in SE's TOS, but it definitely doesn't apply to posts which have not been edited after that change.

@AleksandrDubinsky While I agree that nothing is really decided prior to going through a court case (i.e. seeing a judge), in almost all (non-small claims) cases, you should put effort into seeing a lawyer prior to seeing a judge. If you're seeing a judge for a legal issue prior to seeing a lawyer, that's usually not a good situation.

Attesting that it's not allowed when you're not a lawyer and have no standing to say pretty much anything in this answer is what leads to the frustrations like Aleksandr shows. Rather than attempting to state things in big bold letters, it makes more sense to rephrase this answer to ask if we consulted lawyers, whether this is allowed, and whether we've considered all the implications. Your answer comes off as arguing for the sake of arguing rather than trying to bring up a legitimate concern that users might have and deserves an answer because your "questions" are buried.

wiki.creativecommons.org/wiki/4.0_upgrade_guidelines according to this, you need to ask.

@animuson Perhaps I've stated what amounts to my opinion, with reasoning, too strongly. I will look at rewording this answer. I have to be AFK for a bit, so it may be a while prior to a revision. The strength of wording probably comes from negative experiences in my own life where other parties have tried to unilaterally change existing agreements (not licensing). My experience is that people commonly don't care about what agreements exist; they just want it to be the way they want it. Allowing those negative experiences to spill a bit into this is answer is unfortunate. Sorry about that.

@DanielA.White As they say in that Wiki, permission only need be obtained, not necessarily asked for. Depending on how SE's TOU were defined, it is possible (and indeed, quite likely) they already have implicit permission to update licensing of content to newer versions simply by virtue of the fact that users agreed to the TOU by posting the content in the first place.

@PMende fair enough true

@PMende While I haven't checked older TOS versions, as far as I could see, the current version of the TOS doesn't say anything about re-licensing prior contributions, or grant a right for SE to change the terms under which prior contributions are licensed. I agree that it's possible for SE to change the TOS to say that by using SE or making new contributions, your old contributions are re-licensed under whatever license. However, being effective requires action of some type on the part of the user (this is briefly mentioned in the end-notes).

The Internet Archive's Wayback Machine has plenty of copies of older terms of service. Here's one from May 1, 2019. Under Subscriber Content, that says such "is perpetually and irrevocably licensed to Stack Overflow on a worldwide, royalty-free, non-exclusive basis pursuant to Creative Commons licensing terms (CC-BY-SA), and you grant Stack Overflow the perpetual and irrevocable right and license to" (do Stack Exchange-y stuff with it).

No specific license version number seems to have been specified in the text, but a link goes to CC-BY-SA-4.0. Curiously, even back in May 2018, the link was to CC-BY-SA-4.0. The corresponding link was to 3.0 in February 2017.

@animuson so have the company's lawyers confirmed whether this is OK?

Related: Is it too late to change the SE content license?

they only have to send mails around to say "hey we have updated this" and then you have 30 days to opt-out of that. If you do nothing, then it is ok.

@OrangeDog I mean, they obviously have?! Do you really think somebody at Stack Exchange decided this change without buy-in from the company lawyers? Uhm, lol. (I’m agnostic as to whether the change is actually legally airtight; but clearly the company lawyers think it’s defensible.)

@KonradRudolph stupider things have been done before, and it certainly looks to me that this isn't allowed. Regardless, if this specific issue has been looked at then all they have to do is say so and we can stop debating it.

Hey, @animuson. Moderator of Open Source here. Still not a lawyer, but plenty of experience with the nuances of open licensing, including CC stuff. FWIW, I believe Makyen is correct - I would need to recheck to be sure, but that's my recollection.

Relevant Open Source question: Do Stack Exchange’s ToS mean that the user-generated content is double-licensed to them?

The (old) ToS do not explicitly state a version number, meaning (I had this confirmed recently for the GPL) “any version” (in the relationship poster→SO/SE). This change affects merely the relationship SO/SE→reader, i.e. the outgoing terms from the network, which stopped issuing a 3.0 licence (but not terminating the 3.0 one for everything that had already been downloaded before the change) and now started issuing 4.0 licences. [That being said, the CC licences are notoriously not sublicenceable, but if the original author grants them all… this isn’t a problem.]

@mirabilos Every version of the TOS which I've read (and I've looked at versions on archive.org for a lot of different dates) links to the legal version of a specific CC BY-SA license. That link defines which version was included in the TOS and what people were agreeing to at that time. If there was no such link, then I'd agree that it would have meant whatever versions of CC BY-SA existed at the time, or the most current. If the link was to a general description of CC BY-SA, with a list of the licenses, it would have been clearer the content was being licensed under any of them. (continued)

(continued) However, even if there had been no link to a specific legal license, the CC BY-SA 4.0 license was published on 2013-11-25. SE would only be able to move old licenses to a newly created version of CC BY-SA if there was explicit wording to that effect in the TOS version at the time the old content was submitted by the user, but that wording doesn't exist in any version of the TOS I've read. Alternately, the existing CC BY-SA licenses would have had to say that a later license can be used for the original content, but that's not the case (at least for 3.0, I have not looked at <3.0).

@Makyen the ToS links to one, but that link is explanatory, the wording explicitly doesn’t specify a version. Doing that they can also release under future versions.

@mirabilos I disagree. The TOS is an HTML document, which includes the URLs. The URLs and the contents of the linked pages inform the meaning of the agreement's wording. As I've said, I'd agree with you, in a limited manner, if the link didn't exist or pointed to a general description of CC BY-SA. But, as far as I have seen, the link has always existed and always linked to one specific version of CC BY-SA at a time. There's likely significant ancillary documents showing SE interpreting it as meaning the linked version. Your interpretation also doesn't cover the issue of 4.0 not (continued)

(continued) existing when earlier content was submitted. I'd also point out that (at least in the places I'm aware of in the US) when there's ambiguity in a contract, the contract is interpreted in favor of the party that didn't draft the contract, as it's assumed the drafter could have made the contract clear, if they meant a specific interpretation. My expectation is that it's unlikely your interpretation would be upheld. However, I'm fine with agreeing to disagree. Without researching case law, I don't think either of us is going to be able to definitively support their interpretation.