# Stack Exchange and Stack Overflow are moving to CC BY-SA 4.0

Effective today, all Subscriber Content on Stack Overflow and the Stack Exchange network will be available under the terms of version 4.0 of the Creative Commons Attribution-ShareAlike (CC BY-SA) license.

This change follows our last Terms Of Service (ToS) update where we inadvertently introduced a point of confusion: the new ToS links to version 4.0 of the CC BY-SA license in support of defining the use of a Creative Commons license, where the previous terms linked to version 3.0 of the license. That’s not a problem itself, but the footer section of our websites continued to specify version 3.0 of the CC BY-SA license; this was an oversight.

It was our intention to update the footer information in a manner that was commensurate with the updated terms. We'd like to thank those from our communities that thoughtfully pointed out the issue and we have subsequently improved our review process.

Today's change will bring things into alignment by updating the information in the footer and we will continue forward under version 4.0 of the CC BY-SA license. This change encompasses all Subscriber Content as described in our ToS including data dumps as well as any content previously made available by Stack Exchange under the terms of version 3.0 of the CC BY-SA license.

If you have any questions about how licenses may or may not impact your business or personal projects, it's better to speak with your own attorney — we can't provide advice specific enough to be of much use in most cases.

4.0 has many advantages, and we encourage you to read the announcement letting the world know it was ready as a starting point if you're curious about the improvements.

We're happy to hear any thoughts about this, particularly from those in our international communities. If you've got questions pertaining to the change, we'll do our best to answer them, as long as we can answer without giving specific advice.

• For those curious, see what's new in 4.0 here. – TylerH Sep 5 at 15:04
• Just a curious question, why is the whole footer lowercase except your company name? I'd like to see CC BY-SA properly capitalized as it's some kind of abbreviation? – iBug Sep 5 at 15:17
• The Stack Overflow ToS can be interpreted to read that SO receives a CC-BY-SA license from users and additional rights. This relicensing is not possible under the CC license and can only happen if SO has additional rights. Is this confirmation that SO does not consider itself bound by the CC license? Or alternatively, does SO assume to have received a license under all CC-BY-SA versions so that it can choose which version it passes on to the public? I'd just be interested to hear an argument why you've been allowed to do what you've already done. – amon Sep 6 at 8:01
• I don't know if version 4 is really better than version 3 and I wonder if there really was a need for change, but what I really miss is this running ideas concerning the user generated content through the community before. I mean, what if users didn't like CC-BY-SA-4.0 It's more like announcements. Not sure if it ever was different, but somehow it feels like it. Anyway, doesn't really matter. – Trilarion Sep 6 at 17:38
• Tim, has this retroactive change been run by the legal department? I'm no lawyer, but I highly doubt you have the ability to change the license of content that doesn't belong to you. When I have posted answers, I gave you a nonexclusive license under CC BY-SA 3.0. I am the only one who can change that. – jhpratt Sep 6 at 23:43
• @jhpratt, I strongly recommend you read the terms of service: the rights you grant to Stack Exchange are considerably broader than a simple CC-BY-SA. – Mark Sep 9 at 19:50
• @Mark I have read the "subscriber content" section, which is the relevant part here. It's pretty clear that Stack Exchange has the right to use it pursuant pursuant to Creative Commons licensing terms (CC-BY-SA). This post makes clear that that was CC-BY-SA 3.0. Apart from reiterating the commercial side of things, I see nothing else that specifies that Stack may relicense content whose copyright I retain. Perhaps you could point me to something I'm missing? If you're looking at the opening section, that's Stack's content, not user-submitted. – jhpratt Sep 9 at 21:35
• "subscriber content" wasn't defined, and the ToS page makes it sound like "everything", so I'm confused: is code in questions and answers still covered by an MIT license? (or MIT-plus-exception, as described in the meta.stackexchange.com/q/271080/167713 post, which I'd not previously been aware of!) – Darren Cook Sep 10 at 7:00
• @DarrenCook Code in questions and answers never was covered by an MIT licence. The MIT licencing plan that you linked to was postponed indefinitely, as you can see for yourself if you click through. – Emil Jeřábek Sep 10 at 8:44
• Considering the legal blunder that was made and this requiring an incredibly complex solution now (part of the content which has now been added during the past two weeks is CC 4 now), could you guys straight away look at meta.stackexchange.com/questions/327528/… legally as well as it covers the same issue? – David Mulder Sep 13 at 14:42
• @TimPost As SO is international, please could you explain what "all Subscriber Content on Stack Overflow and the Stack Exchange network" means in English rather than what could be regarded as "management speak"? Does it mean that contributions after 2019-09-05 13:63:20Z are affected, or does it mean that all contributions are intended to be affected? I'm sure no malice is intended, but perhaps some licensing implications were not fully appreciated. – Andrew Morton Sep 13 at 22:29
• It's been almost two weeks. Will there be any followup to this at all? Zero staff engagement since these concerns about our content were raised, unless there's been another post that I've missed. Footer still says 4.0. – Lightness Races in Orbit 2 days ago
• The silence on the part of SE is troubling. Several people have raised the fact that this change does not comply with the Creative Commons guidelines for upgrading to 4.0 from previous versions of the licenses, yet there has been no response. To me, the biggest concern is that SE is misrepresenting the license under which content that I have previously provided is available. The second biggest concern is that this demonstrates a lack of a grasp on legal matters and licensing agreements with contributors. Both are serious concerns. – Thomas Owens 19 hours ago

I like CC BY-SA 4.0. IMO, it's better than 3.0. I'd prefer to use it. I've chosen to use 4.0, instead of 3.0, on projects of my own. However, my preference doesn't affect the current situation with respect to existing content on Stack Exchange.

# Stack Exchange doesn't have the right to unilaterally change the license of previously submitted content.

Beyond what might exist in the CC BY-SA 3.0 license, I've seen nothing that indicates Stack Exchange has the right to change the license for previously submitted content. No version of the TOS which I've read grants the additional right to Stack Exchange to re-license prior existing content, or, in the future, to re-license content submitted under the current TOS.

If you believe such a right was granted outside of the CC BY-SA licenses, I would appreciate knowing what wording in which document you feel grants that right.

## Migrating from CC BY-SA 3.0 to CC BY-SA 4.0

The primary issue is migrating from CC BY-SA 3.0 to CC BY-SA 4.0. Unfortunately, Stack Exchange unilaterally shifting the existing license on older subscriber content from 3.0 to 4.0 isn't permitted, or at least that's the opinion of the Creative Commons, who wrote the licenses.

Creative Commons has a 4.0 upgrade guidelines document, which says in part (emphasis mine):

### Upgrading from prior versions to 4.0

Existing content:

• Who owns the rights?
• ...
• If the contributors, then need permission to relicense. Without permission (via terms of use or otherwise), then that content remains under prior version.

• Who owns the rights to the original?
• ...
• If the contributor, then can license new contributions to an adaptation under 4.0 but original contributions remain under prior version unless express permission to upgrade is obtained.

You can change what happens with respect to old contributions moving forward by mutual agreement with the user that submitted the content (i.e. each question, answer, comment, tag excerpt/wiki, and edit). In other words, you can get permission from each author to re-license the content they submitted, but you can not do so unilaterally.1 You could change the TOS such that new use of the site relicenses old contributions by that user, but that's something you should discuss with your lawyers.

However, as a practical matter, you will never be able to get permission from every contributor to switch to the new license for all previously submitted content (e.g. users who never return to the site), which means you must deal with mixed licenses in some manner.

This announcement says that you "inadvertently introduced a point of confusion". This can be read many different ways. One is "the person who was updating the TOS mistakenly typed a 4 instead of a 3 when linking to the CC BY-SA license." The wording you've used makes it sound like the change was a mistake that you just decided to go with. It doesn't sound like you put planning into making such a change.

The fact that the change from linking/saying CC BY-SA 3.0 to CC BY-SA 4.0 did not happen close to seamlessly in all places on the site (or at least most) argues that this was not a planned change. In particular, that CC BY-SA 4.0 has been linked in the TOS for more than a year and you are only getting to making an announcement and other on-site changes now, really makes it look like the change was, at least initially, just a mistake.

If this was not planned and/or you have not yet run this by your lawyers, I strongly recommend that you inform your lawyers of the current situation and ask for their advice.

My belief is that by making this change you've created a quite complex situation, which is difficult to resolve. My understanding is that the resolution recommended by the Creative Commons requires changes to how you display subscriber content (i.e. indicating the applicable license individually for each question, answer, comment, tag excerpt/wiki, and edit).

You might be able to get away with just making it clear as to the date that the license changed, but doing that will require every user who copies content from Stack Exchange to individually determine which license is being used for each portion they copy.

I am not a lawyer. This is not legal advice. This is just my interpretation from reading the license, the current TOS, my memory of the old TOS, etc. I strongly recommend that you seek the advice of your lawyers.

1. You can change your TOS unilaterally, but that doesn't change what agreements are in place from the past. Changing those existing agreements (i.e. the existing licenses) requires action on the part of the other party (i.e. your users).
• Comments are not for extended discussion; this conversation about legal issues has been moved to chat. – Monica Cellio Sep 8 at 3:44
• @MonicaCellio This whole thread is a discussion about legal issues among non-lawyers; I don't understand why this conversation has been singled out. Also, I see nothing wrong with non-lawyers discussing law. Do you also think that only licensed mathematicians can split the bill at a restaurant? – Federico Poloni Sep 8 at 21:06
• @FedericoPoloni there were 26 comments in this specific comment section. Also, this isn't "singling out" - there's actually nothing bad about it. The comments are still preserved, and they're still easily accessible, but in an arena more designed for extended discussions. The comment system just isn't built for it – Olivia Sep 8 at 21:16
• @FedericoPoloni volume, no sign that the discussion was winding down, and flags. Chat works much better for the kind of back-and-forth that people were having; there's at least rudimentary threading in chat, unlike comments, and even though meta is fundamentally about discussions, there are still practical limits. There might be other threads that should be moved too, but flags drew me to this one. – Monica Cellio Sep 8 at 21:19
• I have written to the real lawyers (legal stackoverflow com, at least I hope there will be real lawyers) about this issue some days ago. As soon as I get an answer, I will post it here. I also included my explicit disagreement with the attempted re-licensing, just in case that makes a difference. – Trilarion Sep 9 at 13:58
• @Trilarion Any updates? – called2voyage Sep 10 at 19:28
• @called2voyage Silence so far. If I don't hear anything by Friday I'll send a second inquiry. All I can do. Feel free to also send them a message of your own. Whoever gets a reply first can post it. – Trilarion Sep 11 at 7:53
• @Trilarion the next escalation is to instruct a lawyer to contact them on your behalf, but then it probably starts costing money, unless the EFF want to fund it or something. – OrangeDog Sep 11 at 13:46
• I'd like to point out that they also changed Area 51 to CC BY-SA 4.0 from 2.5. – Peilonrayz Sep 11 at 21:25
• I would presume they would be using the language given in this Answer: opensource.stackexchange.com/questions/7430/…. It claims that section 4(b)(ii) says you can use a subsequent version of the CC license and still be compliant with 3.0. – trlkly yesterday
• @Makyen The answer on opensource.se that I've written does not disagree with the Creative Commons guidance you quote. The linked Q&A discusses the case of an adaptation, but I've also added a paragraph that CC does not support relicensing of existing works: “In this sense, the CC licenses have a compatibility mechanism but no way to do a license migration”. Your view of SE as a collection is interesting, but it leads to the same results as looking at each piece of Subscriber Content individually. – amon yesterday

I have some serious concerns with this, especially after the last round of licensing fiascos around the MIT license.

I want to be clear: I like the Creative Commons licenses for text. I think that CC-BY-SA is appropriate for content contributed to Stack Exchange. I think that CC-BY-SA 4.0 is a fantastic license and I use it myself.

However, you have not obtained my permission to change the license of the content that I have contributed. The Terms of Service did not require me to grant that permission as part of using the service (and even if you added it, you would need to handle the case where someone decides to stop using the service but does not grant permission for existing content) and I have not received a request for permission to update the license of my content.

My biggest concern here, like it was in the last rounds of licensing discussions, is a fundamental misunderstanding of the rules and laws around licensing. This does not give me confidence.

• MIT License fiasco? Can you link me? – George Stocker Sep 6 at 14:36
• @GeorgeStocker Googling the term 'Stack Overflow MIT license' gave me this as the top result: meta.stackexchange.com/questions/271080/… – TylerH Sep 6 at 14:44
• @TylerH Yeah, that's it. The linked post that is lower than -300 is kind of what I was thinking of. – Thomas Owens Sep 6 at 14:46
• So much this. I had a real deja vu moment when I saw this post. Everything I can find says they can't just change the license on existing works, yet that appears to be what they are trying to do. – NathanOliver Sep 6 at 14:50
• @TylerH Even that at least said all new code contributions. That little three-letter word "new" makes an awful lot of difference here. – a CVn Sep 7 at 10:48
• Haven't you licensed under the terms of CC-BY-SA 3.0? From what I read out the 3.0 text version, using 4.0 is first of all fine then (might have been different for 1.0 which you do not relate to). So let me ask more specifically: How can you say, you didn't grant licensing the content under CC-BY-SA 4.0? Didn't the grant of the 3.0 version explicitly allow to license under the later version? Can you help me find the part in the text of the 3.0 license that prohibits using it under CC-BY-SA 4.0? – hakre 19 hours ago
• @ThomasOwens: If you licensed the work under 3.0 I would say restrictions from 4.b. apply which means that permission for a future version (with the same elements, e.g. CC-BY-SA) are already given by the author. As far as I have understood the overall CC license framework this is intended. However as you say, for you personally it is that it requires permission, I can see that as well. So could you say what is different for you between those licensing terms when applied on SO you want to be asked for first? – hakre 8 hours ago
• @hakre I don't know what 4.b you are referring to, but what applies is under the "Existing content" subheader below the "Upgrading from prior versions to 4.0" header, specifically the section on what to do if contributors own the rights. I never, under any terms of use or service, assigned the rights of my work to anyone else. Per the guidelines, all existing content remains under the license that was granted (CC-BY-SA 3.0) and needs to be indicated as such (which is not happening now). In order for the existing content to be relicensed, my permission must be obtained (and it hasn't). – Thomas Owens 8 hours ago
• @ThomasOwens: Sorry this was unclear, 4.b. is the restriction about the license that can be used in the CC-BY-SA 3.0 license text: creativecommons.org/licenses/by-sa/3.0/legalcode - It's the 4. Restrictions and there b: "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; [...] " (highlighting II. here which is about that 3.0 allows to distribute under 4.0, at least how I read it). – hakre 5 hours ago
• @hakre Stack Exchange is a not an Adaptation. That does not apply. A question on Stack Exchange is a collection that includes the content of the question, the content of all of the answers, and the content of all of the comments on either. Each part (question, answer, comment) is also an independent work that is licensed to Stack Exchange individually by its creator. – Thomas Owens 5 hours ago
• @ThomasOwens; It's a distribution (which is even named first of all) and that is under such license. No need to ride on the word "Adaption" too much. Let's just talk about re-use by distributing (copying it, e.g. into the database, into the website when the website is getting displayed, for simpleness, just assume there would be no changes at all to the work (even changes on SO a super common. Q&A form a combined work, often by mutliple authors (e.g. one author write a question, another author writes the answer), but let's just use Distribution here. 4.b has it covered, doesn't it? – hakre 5 hours ago
• @hakre No, it does not because 4.b only apples to adaptations and SE content is not an adaption. If SE made an adaptation of something I licensed to them, then they could release that adaptation under a license that meets the criteria defined in 4.b (which would be CC-BY-SA 4.0). However, since it's not an adaptation, they need my permission to share my work under a modified license. 4.a and 4.c apply where 4.a applies to my specific contribution and 4.c applies to the collection that contains my contribution along with other contributions and neither of those permit changing the license terms – Thomas Owens 5 hours ago
• @ThomasOwens: I think 4.b reflects the compatibility Would make sense in a wiki like editing experience. It's even the upgrade document that says a lot here about compatibility, two excerpts: "As a practical matter, compliance with a later version of a license is typically compliant with the earlier license." and "The definition of NonCommercial is unchanged from prior versions, and the scope of ShareAlike has only expanded, so looking only at the later license should not be problematic vis-a-vis those license elements.". – hakre 3 hours ago
• @ThomasOwens: Would you see a concrete violation in the terms for the proposed change? Is there anything different for the requirements with the original work? Which terms in 4.0 would violate which terms in 3.0? – hakre 3 hours ago

As animuson wanted this phrased as a question:

Are you sure you're legally allowed to relicense all content without asking the copyright holders (i.e. all contributors) individually for permission? If so, by what justification? As detailed in other answers it looks like CC-BY-SA 3.0 doesn't allow it.

The previous relicensing plan explicitly did not apply retroactively.

I just saw that in April 2011 you unilaterally changed all content from 2.5 to 3.0 without any legal explanation. I imagine back then almost nobody noticed. It seems this was after a similar accidental change to the terms.

• Hopefully the lawsuits SE will now get won't make it go bankrupt, it's still useful. – Shadow The Dragon Wizard Sep 10 at 11:52
• @ShadowTheDragonWizard (un)fortunately "PLEASE BE AWARE THAT BY USING THE PUBLIC NETWORK, EXCEPT FOR CERTAIN TYPES OF DISPUTES DESCRIBED IN THE SECTION TITLED “MANDATORY ARBITRATION” BELOW, YOU AGREE THAT ALL DISPUTES BETWEEN YOU AND US WILL BE RESOLVED BY BINDING, INDIVIDUAL ARBITRATION AND YOU WAIVE YOUR RIGHT TO PARTICIPATE IN A CLASS ACTION LAWSUIT OR CLASS-WIDE ARBITRATION." – OrangeDog Sep 10 at 11:54
• meh... surely people will find ways around it. – Shadow The Dragon Wizard Sep 10 at 11:57
• @aCVn oh yeah. I think I did that :) – OrangeDog Sep 10 at 12:41
• @aCVn That's wonderful for those of us that never did because they never provided the secure means that was promised. – jhpratt Sep 10 at 15:20
• Of course, any former contributors who stopped using Stack Overflow before May 2018 will not have agreed to the new ToS with the binding arbitration clause in any form, nor can they have consented to this license change (unless they somehow did so in advance, e.g. announcing on their user profile that SE is free to relicense their contributions under any CC-By-SA version). There seem to be quite a few such users, even ignoring those who have deleted their accounts. – Ilmari Karonen Sep 11 at 13:25
• @OrangeDog: EU citizen here, I can just waive that whole "mandatory arbitration". And to counteract all those caps, I HEREBY WAIVE MANDATORY ARBITRATION. – MSalters 6 hours ago

Another subtle way in which the move to 4.0 is problematic is the following: CC-BY-SA 4.0 requires that any change made to the source material must be explicitly marked. And two changes that SE makes automatically to all published content are:

These changes must now be explicitly marked as modifications.

• Insofar as these count as modifications that need to be marked under CC-By-SA 4.0, there are plenty of others that SE also automatically makes to all posts. Besides the big and obvious one (submitted content is in Markdown, SE converts it to HTML for presentation), there's also code syntax highlighting on SO, MathJax rendering on Math.SE, automatic conversion of YouTube links to embedded iframes on Movies.SE (which is not even currently shown in the edit preview!), etc. All of these may also change at any moment, even if the post is not edited by its author or anyone else. – Ilmari Karonen Sep 6 at 8:37
• @IlmariKaronen Personally I consider them to be two different categories. What you mention is simply "rendering" the Markdown code in a convenient way; it is an operation that alters form but not content. Changing the target of a hyperlink the content creator has provided is something different. – Federico Poloni Sep 6 at 8:53
• Certainly some of the changes I listed can be regarded as mere technical modifications needed to convert the content from Markdown to HTML; but then, so can the addition of nofollow attributes, given that the Markdown link syntax provides no way to specify whether a particular link should have the attribute or not. And the YouTube link-to-embed conversion most definitely does change the URLs, even beyond the fact that it turns them from clickable links into iframes. (It basically just extracts the video ID and the start time from the URL, and discards all the rest.) – Ilmari Karonen Sep 6 at 9:18
• @FedericoPoloni If the HTML is just a presentation of the content then adding nofollow does not change the content, it's just something added to the presentation with no visible difference. – Giacomo Alzetta Sep 6 at 9:20
• Anyway, I have no particularly strong opinion on whether the changes you mention are desirable (if anything, I rather wish SE wasn't so eager to slap nofollow on all the links) or something that needs to be marked as modifications under CC-By-SA 4.0. I merely wanted to point out that you seem to have cherry-picked two specific controversial parts of the SE Markdown-to-HTML conversion process and ignored all the rest. – Ilmari Karonen Sep 6 at 9:23
• OK, let's forget about nofollow for a second; how is rewriting affiliate links part of the presentation? There is no visible change in the landing page on Amazon up to now (only to someone's wallet), but nothing guarantees that it will always be the same. It's Amazon's proprietary API, they are changing some HTML get parameters. – Federico Poloni Sep 6 at 9:55
• It also says "For trivial modifications, such as correcting spelling errors, it may be reasonable to omit the notice." I would consider your examples as more trivial than that, even if they were made to the actual content and not the presentation. – OrangeDog Sep 6 at 16:57
• If this is true, is stackoverflow.com/help/referencing now out of date? Is an extra bullet point required? If the content is from the stack exchange network, indicate whether you have modified the original in any way. – dbc Sep 6 at 17:42
• @dbc No, those guidelines apply to quotations and similar things. Referencing != reproducing. – Federico Poloni Sep 6 at 19:54
• @FedericoPoloni - I'm specifically thinking of a situation where I copy some code from another question or answer and make some modification. I've been following those rules in such situations: 1) Give a link; 2) Copy only the necessary code; 3) Name + link of the original author. Do I now need to do 4) Explicitly indicate whether & how I modified the code? – dbc Sep 6 at 20:09
• @dbc No, if I understand correctly you just need to write that you modified the code, not how. – Federico Poloni Sep 6 at 21:21
• OK that's not hard then. But it sounds as though stackoverflow.com/help/referencing now needs an update. I'll add an answer pointing that out. – dbc Sep 6 at 21:27
• @FedericoPoloni A quotation is a reproduction. The example given by CC is a quoted excerpt. – OrangeDog Sep 7 at 9:24

While we are here ....

This is related enough to be mentioned here.
When images are copied to Imgur they are not only notionally assigned CC-by-whatever-the-current-flavour-is rights BUT also are subject to Imgur's TOS for unpaid Imgur posts. These are draconian. I raised this issue some years ago and was assured at the time that the Imgur conditions applied to paid Imgur contributions would be applied. However, in 'no time flat' the language used made it clear that committing an image to Imgur storage was (allegedly) waiving your rights to it.

But wait - it's worse ... . So if you LINK to an image because embedding it would result in SE CC-by-xxx ing it, and Imgur making off with it, and if somebody then converts the link to an Imgur stored image, as people'helpfully' do on an ongoing basis, then notionally the helpful editor has assigned CC-by-xxx to your image and given Imgur the right to have their irrevocable way with it without you knowing, let along having been asked what you think.

No?

Rene helpfully located my question and its "answer" from 7 years ago here

There Imgur is cited as saying
"Although we don't sell the images or grant usage for them at all, it is in the terms that we have the right to do so." That is what I was querying then.
Does this apply now?

'Back then', Jaydies, on behalf of SE said "We have a contract with Imgur LLC that explicitly states:

Imgur will make no claim of copyright to any images stored by SE on the Image Server (other than Imgur's own copyrighted images and other works, if any)."

But, the question is not whether they own copyright but whether they have or claim to have been granted the right to have their way with images in an unlimited manner. That they believed that they had the right then appears to have been the case, quite regardless of copyright.

"While we don't .... we have the right ..." is precisely what the current question is attempting to deal with.

Also relevant:

imgur, copyrighted images from the web, and imgur accounts

• I would expect that a third party, such as your mentioned helpful editor, cannot give Imgur, nor any other entity, a valid license to the image as it is not theirs to license in the first place. That of course raises the new question about whether they have the right to upload it to Imgur at all, or if that should technically constitute copyright infringement. (By whom; the editor, or Imgur, or both?) – a CVn Sep 8 at 20:08
• @aCVn I agree with your points. These have been raised directly or by implication in past discussions afaik. This does not stop people giving Imgur an invalid licence (and it happens), both to images owned by SE posters and to images they have cited. ||We also seem to have reverted to the state where "Imgur OWNS your images" once they are posted to Imgur, even though they had CCbyxxx status while transiting SE. [People posting images to Imgur using a free account are effectively assigning open slather rights to them in perpetuity. ] ... – Russell McMahon Sep 9 at 7:03
• @aCVn ... AFAIK the SE status of Imgur hosted images is the same. I was assured that this would be changed when I noted it some while ago but we seem to be back where we were.]. – Russell McMahon Sep 9 at 7:04
• I assume SE pays imgur for their service so I doubt the "unpaid" claim is at play here. Imgur will make no claim of copyright to any images stored by SE on the Image Server (other than Imgur's own copyrighted images and other works, if any) source – rene Sep 9 at 16:29
• @rene I'll leave this here incomplete and start another comment: I discussed this with [person at other end of a link]. The written terms were as for the unpaid service. | I was assued by an (as I recall) SE person that this would be changed. Indications have been for some while that the wording is now and/or still as it was. | A wade through the Imgur terms that were applied made it clear that they for practical purposes owned the copyright. – Russell McMahon Sep 9 at 19:14
• @Rene That is (as you will no doubt be aware) my original query from 7! years ago. | Looking at the edit history (which I just did) shows that some of the explicit Imgur comments have been edited out of my post and it is uncertain what the situation is BUT it looks as though it applies as I say above. Back then Imgur said: "Although we don't sell the images or grant usage for them at all, it is in the terms that we have the right to do so. If you delete your image, we no longer have the right, so it is perpetual for the duration of its time on our website.". BUT they also note that on ... – Russell McMahon Sep 9 at 19:20
• @rene ... free accounts images are HIDDEN (not deleted) so the last N only are visible. To delete them you'd have to keep track of the ones visible and may or may not be able to locate the hidden ones. || If we are having this discussion re V3 to V4 licence change and whether it is potentially onerous or whether the V3 licence prevents a change to V4 without user permission - the WHY do we think it's clear that the SE site CC (3 or 4 or ?) licence prevents Imgur's terms applying? – Russell McMahon Sep 9 at 19:25
• Again: IMGUR themselves said "Although we don't sell the images or grant usage for them at all, it is in the terms that we have the right to do so." – Russell McMahon Sep 9 at 19:25
• What is the source for the claimed statement from Imgur in your question that you keep repeating? Who asked them, what exactly they asked them, and where is it recorded? There is an actual answer posted by an actual Imgur employee that says something completely different. – Emil Jeřábek Sep 10 at 8:24
• @EmilJeřábek 1. Did you read my post from 7 years ago [here]()? 2. Please provide a link to and identify what you mean when you say "There is an actual answerposted by an actual imgur employee ..." 3. Have you noted that you retaining copyright to your material does not stop imgur doing whatsoever they wish with it IF you licence them to do so? ... – Russell McMahon Sep 10 at 14:07
• @Emil ... 4. Note in current Imgur terms : " ... With regard to any file or content you upload to the public portions of our site, you grant Imgur a non-exclusive, royalty-free, perpetual, irrevocable worldwide license (with sublicense and assignment rights) to use, to display online and in any present or future media, to create derivative works of, to allow downloads of, and/or distribute any such file or content. ..." From Here. || Unless a clear 'map' of the process & related documentation is available users cannot be sure that what appears to be being done isn't. – Russell McMahon Sep 10 at 14:08
• What you just quoted are terms of Imgur’s public free hosting service. They are irrelevant to the usage of SE’s paid private Imgur account, whose terms of service are given solely by the contract between SE and Imgur. Your 7 year old question is answered by authoritative answers of both an SE emplyee (Jaidles) and an Imgur employee (rrrah), who make it clear that as per the contract, no rights to the hosted images are transfered to Imgur. As far as I can see, you are just spreading baseless FUD. – Emil Jeřábek Sep 10 at 16:14
• You have not provided any reference whatsoever for your claim in meta.stackexchange.com/q/137714 that “Although we don't sell the images or grant usage for them at all, it is in the terms that we have the right to do so” (that you keep repeating here), nor you have answered any questions that I raised about it. This is FUD plain and simple. The two answers that I mentioned are also in meta.stackexchange.com/q/137714 . I assumed that you read that, since you keep telling everyone else to do so. – Emil Jeřábek Sep 11 at 6:35
• @EmilJeřábek I'd hoped we might be able to settle down to a somewhat more reasoned discourse. || Thanks for the source of the 'rrrah' comment - I'd missed that name. She quotes a lawyer reiterating what Michael Pryor said - and then quotes an excellent example of my XXX / YYY dichotomy. | She says "We have a contract with Imgur LLC that explicitly states: Imgur will make no claim of copyright to any images stored by SE on the Image Server (other than Imgur's own copyrighted images and other works, if any)." || This in NO WAY says that Imgur does not claim the right to use your images ... – Russell McMahon Sep 11 at 11:02
• ... in any way they wish - it just says that you retain copyright. That matches my above XXX / YYY case. [Copyright retention is not necessarily not loss of all rights] || I will be very happy if someone authoritative in one place provides links to the agreements that exist. 'Simply' stating that "we have agreed xxx" which implies "yyy" and asking people to take it on trust (with or without the statement that I do NOT at present have a link to) does not make the claims true. As above, I am not saying that purposeful falsehood is intended. – Russell McMahon Sep 11 at 11:07

I wonder if this means that compatibility of the content with Wikipedia content is broken now. I think Wikipedia still uses CC-BY-SA-3.0 and typically these licenses are not backward compatible.

Could I use newly generated content from here still in Wikipedia?

If this isn't the case, I don't like it.

• So it is, link: en.wikipedia.org/wiki/… – dbc Sep 6 at 17:48
• "According to the WMF legal team, CC BY-SA 4.0 is not backwards compatible with CC BY-SA 3.0. Therefore, mixing text licenses under 3.0 and 4.0 would be problematic" - WP:COPYPASTE – OrangeDog Sep 7 at 11:38
• In general you couldn't use content from here in Wikipedia anyway, due to WP:SOURCE. – OrangeDog Sep 9 at 14:04
• @OrangeDog Do you mean that SO is not authoritative? At least for the more useful questions and answers the content is made by professionals in the field. – Trilarion Sep 10 at 8:25
• @Trilarion there are very very few answers that would be suitable encyclopaedia content, are not tertiary sources themselves, do not reference Wikipedia and are written by verifiable authorities. – OrangeDog Sep 10 at 8:29
• @OrangeDog Jon Skeet has hundreds or thousands of answers with a score higher than 100 alone. Would he count as a verifiable authority? I don't know. I would probably count him as verifiable but not everything he posted here as notable. – Trilarion Sep 10 at 9:49
• @Trilarion read the Wikipedia policy. You can cite his books no problem. You can legally copy his (CC-BY-SA 3.0) answers into Wikipedia, but you'd need citations for that content beyond the content itself. – OrangeDog Sep 10 at 9:54
• @OrangeDog: There are plenty of secondary sources (linking directly to language specifications, which are primary by definition). Some of those answers are even written by the very same people who co-wrote the primary source. IMO, the chief problem with using SO content Wikipedia would be a disagreement what stands above primary sources. On SO, that would be math and logic, on WP it's generally the page owner's opinion. – MSalters 6 hours ago

I think it would be better to provide a choice (like YouTube, DeviantArt and some other websites do): CC BY-SA 4.0 as default value for new content, and 3.0 for old content. And of course MIT :)

• In theory, this could be a good solution, especially if the selected license is shown somewhat prominently along with the answer text. In practice, it seems to create uncertainties of its own. What if I change my mind after posting the answer? (In either direction: less restrictive to more restrictive, or the other way around.) What if I change my mind back again later? What if someone else makes an edit and they want their (perhaps substantial) edit to be under a different license? What if an unrelated third party changes the license? (You'd hope that doesn't happen, but in theory it could.) – a CVn Sep 7 at 10:53
• @aCVn you cannot revoke any of the licenses, so changing your mind is irrelevant – OrangeDog Sep 7 at 11:41
• @aCVn just see solutions in any existing open-source project, for example Linux that has many edits :) Changing a license can simply be disabled after publication. – andreymal Sep 7 at 14:17
• I like this idea for most sites, but there's a problem. For a post with a block of code that meets the bar for copyright protection, you would probably need two licenses. The CC licenses are inappropriate for code, and code licenses (like MIT) are inappropriate for text and images or combined work of text, images, and code. – Thomas Owens Sep 7 at 15:08
• @andreymal The Linux kernel is for all intents and purposes stuck at GPL 2 only precisely because that's the license that was set early on (and as I recall, even that was a relicense from Linus' original, more restrictive license). That's a big reason why a lot of free software that's under the GPL specify "GPL/LGPL/AGPL/... version X, or at your option any later version", for some value of X. – a CVn Sep 8 at 10:45
• @OrangeDog Two words: dual licensing. Though you're right, rescinding an already offered license is a different kettle of fish. It raises the question though what happens if someone only comes across the content after the license change. Generally, I stand by my main point: good idea in theory, very complex in practice. – a CVn Sep 8 at 10:46
• @aCVn "What if I change my mind after posting the answer?" -> Toooo late except if the old terms are not violated by anything in by the new. . | "What if I change my mind back again later?" -> As above. "What if someone else makes an edit and they want their (perhaps substantial) edit to be under a different license?" -> As above only. All "GPL" type licences expressly state that alterations editions ... must follow the original terms AND perpetuate them. "What if an unrelated third party changes the license?"-> Unpermitted and it can't legally in any way EXCEPT as above. – Russell McMahon Sep 9 at 8:55
• So, we will allow clueless newbies that can't write anything in proper English asking why their nooby javascript code prints "undefined" to choose how they want to license their question including all the code that they just copied from somewhere else in the internet, even if they don't know nor care anything about licensing? – Victor Stafusa Sep 9 at 17:05
• @aCVn, Linus Torvalds hates GPLv3, so it's disingenuous to claim Linux is stuck at GPLv2 only because that's what was chosen early on. – Wildcard Sep 9 at 19:31

Can you please at this time also remove the trademark violating demand that attribution be given in specific bespoke ways from the footer link and help centre, as I believe was your plan when the new TOS was adopted. (TL chat link).

I see that the link at the bottom of Area 51 now goes to version 4.0 of the license, instead of version 2.5 as it did previously.

However, the footer continues to specify the name of the license as "CC-Wiki", which is an old, deprecated alias name of the CC BY-SA license that was discontinued back when the 3.0 licenses rolled out:

Can that please be changed to say "CC BY-SA 4.0" instead of "CC-Wiki"?

• Or put it back to what it was before until the legal problems with this change have been resolved. – Lightness Races in Orbit Sep 9 at 22:00

You agree that all Subscriber Content that You contribute to the Network is perpetually and irrevocably licensed to Stack Exchange under the Creative Commons Attribution Share Alike license. You grant Stack Exchange the perpetual and irrevocable right and license to use, copy, cache, publish, display, distribute, modify, create derivative works and store such Subscriber Content and, except as otherwise set forth herein, to allow others to do so in any medium now known or hereinafter developed (“Content License”) in order to provide the Services, even if such Subscriber Content has been contributed and subsequently removed by You.

So all subscribers are granting content to Stack Overflow under two licenses :

• Creative Commons Attribution Share Alike
• The previous quoted paragraph starting with "You grant Stack Exchange..."

The current text is different:

You agree that any and all content, including without limitation any and all text, graphics, logos, tools, photographs, images, illustrations, software or source code, audio and video, animations, and product feedback (collectively, “Content”) that you provide to the public Network (collectively, “Subscriber Content”), 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 access, use, process, copy, distribute, export, display and to commercially exploit such Subscriber Content, even if such Subscriber Content has been contributed and subsequently removed by you as reasonably necessary to, for example (without limitation):

But it is still the same two licenses.

As a non-lawyer I get the impression that the second license pretty much lets Stack Overflow do anything they want with subscriber content including but not limited to publish it under CC-BY-SA-4.0 without agreement from original poster.

Though it can be argued that neither of those paragraphs include the term "relicense". We are granting only the right to "use, copy, cache, publish, display, distribute, modify, create derivative works, store and, [...], to allow others to do so [...]". So that and only that, nowhere are we granting the right to do any of those things under different conditions, which is what a change of license means.

Which interpretation is right about this 2nd license allowing the unilateral change to CC-BY-SA-4.0 can only really be discerned by a lawyer judge. But in both cases I consider the 2nd license to be excessive and granting way too many privileges to Stack Overflow while stripping contributors from the protections that CC-BY-SA aims to achieve.

# Which is why I propose:

• Granting of 2nd license of the ToS should be removed from now onwards. Stack Overflow should not have a privileged license which other users don't have. As a user of SO I contribute content as a means to share knowledge equally with everyone. SO is a medium and I don't mind if they profit from providing such medium, we also profit from using it. But I most certainly dislike contributing while being stripped of CC-BY-SA protections by having to agree to this 2nd license. One of those CC-BY-SA protections being that license terms can't be changed by the licensee (this protection is stated in Section 4 of CC-BY-SA 3.0) .
• ToS should explicitly state that content is provided under CC-BY-SA versionX or later. So as to not encounter ourselves in the potential future situation of being stuck with a then old CC-BY-SA version with known problems.
• If you disagreed with the much more permissive licence SE has, you're free to post elsewhere. Its just something that I suspect gives them leeway and what they need to do, well stuff like this – Journeyman Geek Sep 8 at 13:42
• There is an important distinction. Even with the additional license (which should be nuked from orbit, I agree), I grant Stack Exchange the right to do whatever they do with my posts. Nowhere is it written that this right is transferable. If SE republishes my content under CC-BY-SA-4.0, they are not only displaying, exploiting, etc. my work, which is their right, but they are also granting everyone else the right to do the same under that license. And they can't do this: they don't own these posts, they just have obtained special permissions on them by their rightful owner. – Federico Poloni Sep 8 at 15:14
• @FedericoPoloni That is a very good point. Indeed nowhere does it say "relicense". I'm going to incorporate that in my answer. – Jose Antonio Dura Olmos Sep 8 at 21:40
• – unor Sep 9 at 8:28

What's the practical difference between 3.0 and 4.0?

What protections does it lend me as a content creator, and do I lose anything from the change?

• One important change is that it supplies a 30-day grace period for people who use the work without following the license to correct the violation. – Sonic the Anonymous Hedgehog Sep 8 at 17:08
• Another difference is that you can use CC 3.0 content to write a CC 4.0 answer (assuming they're both CC-BY-SA specifically) but not the other way around. So if we stayed on 3.0, eventually it would become harder to write SE answers because we'd be able to reuse less content. However, that has nothing to do with relicensing old questions and answers, which is what all the fuss seems to be about. – Kevin Sep 9 at 15:53
• The first undeleted comment under the question currently links to a 'whats new in 4.0' page, btw. – TylerH Sep 9 at 15:58
• The biggest change in terms of "rights lost" is that under 4.0, you agree to waive database and moral rights to the greatest extent possible. In terms of protections, an end user explicitly gains the right to break any DRM applied, while an author gains the right to include a URI as part of the attribution, and to request removal of attribution at any time for any reason. Most of the rest of the changes are minor adjustments to make the CC licenses easier to comply with in various situations. – Mark Sep 9 at 20:10

If this is being done to bring the licensing footer, TOS, and everything else into agreement, well... that's a not awful reason, though it is problematic.

There is some suggestion that this is being done to have everything under a better and more consistent license and changing the license on past contributions... that gets problematic. If Stack Overflow corporate is claiming that they have the rights to relicense contributions under a different creative commons license, do they have permissions to relicense under a 5.0 version in the future (that may be objectionable) or under CC0 now?

This strongly echos the GPL and that there are people who agree with GPL2 but not GPL3.

If Stack Overflow claims the rights to relicense from CC 3.0 to CC 4.0, do they also have the rights to relicense to CC0? Or CC-BY-NC?

If there is permission to relicense to a specific set of licenses, where is this spelled out?

If there is permission to relicense to any license, where is this spelled out?

Saying "we're doing this, its good for you, trust us..." well, a lot of trust has been burnt in the past and this isn't likely helping.

• "This strongly echos the GPL and that there are people who agree with GPL2 but not GPL3." That particular one is rarely a big problem in practice, though. You generally have two cases with the GPL specifically; licensing under (for example) "GPL v2" (specifying an exact version) or, say, "GPL v2 or, at your option, any later version". In the first case, the version is fixed; in the second case, it allows the licensee to choose, but said licensee has to comply with the full terms of the license version they choose. – a CVn Sep 8 at 20:14

The post title is a bit confusing, can it be stated; All our network ... in example. (or just the network ...)

I ask as I'am contributor on serverfault.com (same could apply for superuser.com's users), and I seen the new as it's featured. I guess our sites will be on 4.0 version too as inside the post it's told "Stack Exchange Network...", but I had to read it to feel included in the change

I ask as some project are stated for StackOverflow only, and sometime for StackExchange's only, like in your title, but those projects are never done for any sub sites.

A major move like that I hardly imagine that it's not for all the networks.

• The title of the post says "Stack Exchange and Stack Overflow". Stack Exchange means the whole network, not just the individual site of Stack Overflow. – Rand al'Thor Sep 7 at 15:19
• @Randal'Thor I think at first it could mean MSE and SO, but yes after reading I seen it’s wrote for all. usually they add network in the title, like seen there; meta.stackexchange.com/questions/300829/… – yagmoth555 Sep 7 at 17:23
• @Randal'Thor Actually, Stack Overflow is the company and the stackoverflow.com website, Stack Exchange is the network of websites. (from what I understand). stackoverflow.blog/2015/09/15/… – Ismael Miguel Sep 8 at 2:43
• @IsmaelMiguel Yes. – Rand al'Thor Sep 8 at 7:29
• @IsmaelMiguel The company is still Stack Exchange Inc (check the footer of this page!), but Stack Overflow is a trading name. – curiousdannii Sep 10 at 15:27

(Since there's a potential point of confusion - I'm a community moderator here and my viewpoints are in no way official except when quoting an official source, neither do they represent the views of the moderation team or anyone other than myself. I know as much, or as little as any of you.)

Since this came up during a conversation on chat, and there's no official answer pointing this out...

We've actually had a license switch before. Amusingly, it was similarly messy with two or three different licence names. There was a lot less fuss then and Stack Exchange apparently survived this.

To quote Shog on chat:

Because, that's really what the CC license is about here: protecting y'all from us. Or from whoever buys us. If you look at the history that motivated licenses like this, that was generally the thing that happened: company solicits user contributions, then makes 'em private, then sues former users for trying to reuse their own content.

The main goal here is so Stack Overflow (the company) or their successors cannot take their ball and go home. They can't do a hyphen site, hide everything we've done so far behind a paywall then go full evil and try to sue users for posting their own content as was on SE.

So, let's talk about some practical considerations. I've been under the impression so far that we license our content to SE - under the understanding that it would be released under the CC BY-SA license and other additional conditions - as per this other answer.

First, it would be practically impossible to contact every single user who has ever contributed anywhere on the network to get an agreement.

Stack Overflow reserves the right, at its discretion, to modify these Public Network Terms at any time by posting revised Public Network Terms on the public Network and by providing notice via e-mail, where possible, or on the public Network.

And well, they provided notice on the public network that they were changing the version of the CC license in use. In theory, and in practice, I don't think anyone would fault anyone else for reproducing content as per the CC licence in use at the time when something was republished.

There's no major change in how we post things and how SE uses them - only how a third party is allowed to use them. This is pretty important. I doubt anyone would fault the use of the CC-Wiki or 2.5 before April 8, 2011, and 3.0 up until this change.

And practically, by insisting that SE gets explicit permission from every single contributor, well that's throwing a brick wall in front of updating the license version without any real way to get around it. There's literally no room to budge if you take that view.

And fundamentally, outside "they're changing a thing without asking us" I'm unclear as to what's the downside here. It's a newer license covering what you see on the page now if you need to use content you didn't generate.

It's also worth considering how and where these licenses are used - scrapers probably could be a group of people targeted, but otherwise knowledge on SE tends to be used pretty widely with no real barriers.

• We are not throwing a brick wall in front of updating the license. Stack Exchange threw it themselves by being sloppy when writing the contract: no "3.0 or later" clause, a lot of confusion and unclear terms about which version of the license applies. In this thread we are just pointing at the words that SE wrote in the terms and conditions. – Federico Poloni Sep 9 at 6:21
• I didn't say we or they. Merely the practical implication of that specific viewpoint. – Journeyman Geek Sep 9 at 6:22
• Also, note that the clause you mention in your second quotation ("reserves the right ... to modify these Public Network Terms") is not retroactive: a change in the TOS would apply only to newly created content, and is not sufficient to make this relicensing legally sound. – Federico Poloni Sep 9 at 6:24
• And that's covered by the rest of my answer. That the licence covers content as per the website at the time, that there's precedent and that its not going to retroactively affect content already licenced under previous versions on external sites. – Journeyman Geek Sep 9 at 6:29
• Side note about "They can't […] hide everything we've done so far behind a paywall." -- Everyone has the right to do this. Only Creative Commons licenses with the "NC" (non commercial) element would prohibit it. – unor Sep 9 at 8:35
• License confusion like this makes it more complicated for anyone else to legally rehost the content in the event SO becomes paywalled or purchased. I wouldn't put it past an evil buyer to sue over distinguishing 3.0 from 4.0 content, even if only to make the rehoster pay their laywer. If preserving rehostability is the point of the license, this is hurting, not helping. – Jeffrey Bosboom Sep 9 at 8:43
• @JeffreyBosboom "I doubt anyone would fault the use of the CC-Wiki or 2.5 before April 8, 2011, and 3.0 up until this change." I've tried to address that. – Journeyman Geek Sep 9 at 8:45
• "There's literally no room to budge if you take that view." What else are contracts for if not to nail down specific parameters so they can't "budge"? If a legal document leaves "no room to budge", well, in the general case that's working as intended, and can be very valuable indeed. If SE wants to change provisions that were already negotiated, well, SE will just need to renegotiate, won't they? That's how contract law works. That's the whole point! – Nathan Tuggy Sep 10 at 3:06
• "And fundamentally, outside "they're changing a thing without asking us" I'm unclear as to what's the downside here." Creative Commons is designed and intended for the express purpose of making sure (almost) anyone can absolutely rely on being able to legally reuse the material without worrying about someone unilaterally pulling the rug out from under them. If SE thinks they can pull the rug out, even so much as just changing license versions, they are dead wrong and have forgotten the point of the license they chose themselves. – Nathan Tuggy Sep 10 at 3:08
• @NathanTuggy Seeing as the "fix" (if necessary) will just be a terms of service update saying that, by not deleting your content you agree to the relicense (as well as relicensing to subsequent versions), that rationale seems overly hostile. No one seems to object to the license itself--they just are worried that a site they use and support will get itself in legal trouble. It's not about the site itself being bad pulling some sort of trick, just the Creative Commons licenses actually making sharing more complicated rather than less as intended. – trlkly yesterday
• @trlkly: There's no way anyone could make "if you don't delete your content you agree to relicense it" fly. Maybe "if you continue to use this site you relicense your content", but there are a lot of users that don't continue to use the site. SE has to either actually get them to agree, or mark their content with a different license. – Nathan Tuggy yesterday

I'm gonna make this a top level answer, because it's been brought up in multiple previous answers.

I believe they are using the CC license itself to grant them the ability to unilaterally move all content from 3.0 to 4.0. I found this Answer when I looked up "how to migrate from CC 3.0 to 4.0". It quotes section 4(b) as saying the following:

You may Distribute or Publicly Perform an Adaptation only under the terms of:
(iv) a Creative Commons Compatible License.

I am not a lawyer. However, subsections (ii), (iii), and (iv) all seem to indicate that the license for the content can be upgraded, and still be compatible with the original license.

• Section 4(b) applies only to "Adaptations" (see 4(b)'s 1st 12 words). Please see the definitions of "Adaptation" and "Collection" in CC BY-SA 3.0. I don't see any way that what SE provides is not a "Collection". If it is a "Collection", then it is explicitly barred from being an "Adaptation" (this is stated in both the definition of "Adaptation" and "Collection"). Thus, section 4(b) does not apply to what SE provides. Note that an individual post which has been edited does become an "Adaptation", but SE provides a "Collection" of those. – Makyen yesterday
• @Makyen I can easily argue it's an Adaptation. As you say, any edit makes it an Adaptation, rather than a Collection. Only if the content is shown verbatim can it be considered a Collection. And every single post made here is edited before it is shown. As such, it arguably fits the definition of an Adaptation, and not the definition of a Collection. Just because it is clearly a "collection" doesn't mean it fits the definition of a "Collection." They made that definition rather restrictive. – trlkly yesterday
• I'm not a lawyer, but as I understand it, what this section effectively allows you to do is only to license your contributions to the Adaptation under a later CC license version. An Adaptation is legally a derivative work, and can only be distributed with the permission of the copyright holders of both the original work and the derivative. Such permission (a.k.a. a license) can, and usually does, come with restrictions, and if the licenses of the original work and the derivative have different restrictions, you must comply with both of them for the permission to be valid. […] – Ilmari Karonen yesterday
• […] For example, if I release a work under CC-By, the license includes an explicit permission for you to make Adaptations of it and distribute them under any terms you want, as long as you (and everyone else redistributing the Adaptation or making further Adaptations of it) also abide by the terms of the original CC-By license (i.e. correctly attribute the original work to me). […] – Ilmari Karonen yesterday
• @Makyen: A copy still is a work based on the work (in that very beginning of what an adaption is), the further ongoing of that pargraph goes into more details what an adaption further on would construe (incl. recast if copy is too generic for you what an adaption (with no change) still an adaption is even you don't want to see it so. What this is about is that the user of a work who is not the author gains rights as licensed per the original author. This includes creating his/her own verbatim copies. A collection comes with it's own rights (for the collection itselfs) which explain it's ment.. – hakre 20 hours ago
• @hakre: That would prove far too much, as then it would be trivial for anyone to relicense any CC work away to any other license they wanted. That's clearly not the case. – Nathan Tuggy 16 hours ago
• @Nathan: Not so sure I get what you write. There are specific restrictions to choice of license, they are named in the (3.0) license. One of the restrictions is to use a newer version of the license (and only with the same elements, e.g. CC-BY-SA here) for the CC-BY-SA 3.0 licensed work. I thought only the scenario to use 4.0 for 3.0 licensed works is on discussion. – hakre 8 hours ago

There is something in the ToS that I don't understand.

You agree that any and all content, including without limitation any and all text, graphics, logos, tools, photographs, images, illustrations, software or source code, audio and video, animations, and product feedback (collectively, “Content”) that you provide to the public Network (collectively, “Subscriber Content”), 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 access, use, process, copy, distribute, export, display and to commercially exploit such Subscriber Content, even if such Subscriber Content has been contributed and subsequently removed by you as reasonably necessary to...

Does this mean that the content we, users add here belong to Stack Overflow and not to us?

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• This should probably be a separate question, rather than an answer to this one, but my understanding is that yes, our questions and answers belong to the Stack Exchange community, not ourselves. – F1Krazy yesterday
• No - as per... a few answers, it belongs to you, but SE has the right (licence) to use it forever (perpetually) and without a way to go "Nope, I don't want my content there any more". – Journeyman Geek yesterday