Currently there's a big controversy over SE changing the licensing from CC 3.0 to CC 4.0. Regardless of whether this change was legally solid or not, could someone provide a specific example of how this licensing ambiguity affects our ability to copy, share and reuse content published on SE in the past?

Let's say I find an interesting piece of code on Stack Overflow from 2017 and add it to my open source project with attribution, citing CC BY SA. Could the author of this piece of code claim a copyright violation somehow, given the licensing ambiguity? The way I see it - the code is licensed under either 3.0 or 4.0 and the difference between the licenses is so small in practice that knowing the exact version shouldn't matter. Whoever wrote the code couldn't suddenly claim that the licensing change completely revoked their original CC attribution, making it impossible for others to reuse their content.

Note that I'm not interested in whether or not the licensing change was legal/moral/appropriate/cool. I'm merely asking about how it affects my rights to reuse content posted on SE.

Relevant posts on other sites:

  1. How do you write an attribution if there's ambiguity over which version of Creative Commons applies?
  2. In which context would the difference in licensing rules between CC BY-SA 3.0 and CC BY-SA 4.0 actually matter?
  3. Is there an official guideline from Creative Commons on how a CC-BY-SA 3.0 website could "upgrade" to CC-BY-SA 4.0?

The aspect in which the uncertainty about the license change affects me most in terms of practical considerations is that the usage of the content outside of Stack Overflow is suddenly subject to complicated considerations.

If I don't know if the content is really CC-BY-SA-3.0 or 4.0, I cannot mix with other CC-BY-SA-3.0 content (because the content could be 4.0) and still claim it's 3.0 (because CC-BY-SA is not backwards compatible). I don't even know what license I should write below this content. ("Hey, this is some content that is either under CC-BY-SA-3.0 or 4.0."). Before I was in safe legal territory, now suddenly I'm not even sure what the license is at all. And people who then want to use my mixed content then will even be more unsure about the license. That's really bad and will surely impede innovation.

For me this is a huge practical hindrance. For Stack Overflow Inc. it may not matter that much because they can use the content for their purpose anyway (independent of 3.0 or 4.0) but for all other thinkable uses of the content it is essential to determine the license beyond doubt (because CC-BY-SA-3.0 is not 4.0). Apart from the differences in the license itself, the most practical problem is indeed the uncertainty about it. And the company has done zero to help bringing certainty. I know it because I have asked them for clarification multiple times and never got any answer. That's why I'm a bit unsatisfied with them.

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    In almost all cases, you can know the license. If it was posted before September 5, 2019 and hasn't been edited since then, it is under CC-BY-SA 3.0 (Creative Commons licenses can't be revoked) and may be under CC-BY-SA 4.0. If it was posted on or after September 5, 2019, it is under CC-BY-SA 4.0 and is not under CC-BY-SA 3.0. If it was posted before the changeover and edited after, it's almost certainly available under CC-BY-SA 4.0, since editing probably counts as creating an "adaptation" for the purposes of the license, which permits upgrading from 3.0 to 4.0. – Mark Nov 8 '19 at 20:24
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    @Mark Is there a way to see the license for each question or answer? – endolith Nov 8 '19 at 21:16
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    @Mark, that's interesting; does that mean that anyone who wants to use a currently 3.0-only post under the 4.0 licence merely needs to edit the post (minorly reword some stuff, for example), and it will automatically become 4.0? – Nate S. Nov 8 '19 at 21:52
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    @Mark Another slight wrinkle: any post made before April 8, 2011 is actually licensed under CC BY-SA 2.5, not 3.0. – Sonic the Curiouser Hedgehog Nov 9 '19 at 0:31
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    Later content may be cc 3 as well, when the poster is willing to dual license – allo Feb 6 '20 at 15:49
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    @endolith: There is now, as of May 2020 - see the post Creative Commons Licensing UI and Data Updates. – V2Blast Aug 2 '20 at 21:48

There are two other changes that are relevant:

  • If you violate the terms of the license, with version 3.0 your rights to use the content are immediately revoked, whereas with 4.0, you're given a 30-day grace period to correct any violation.

  • While you can use 3.0 content in a 4.0 work, you generally can't use 4.0 content in an exclusively 3.0 work. For example, code snippets published after the license change on Stack Overflow can't be posted to Wikipedia, an exclusively 3.0 work. (As far as I can best tell.)

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    can't be posted to Wikipedia. [en.wikipedia.org/wiki/Template:Cc-by-sa-4.0](License template). This template is used on approximately 11,000 pages. Someone should probably tell them 😓 – Pace Nov 7 '19 at 23:19
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    @Pace "This template should only be used on file pages. The text of Wikipedia is a 3.0 work, while other things are licensed under Wikimedia Foundation's terms of use under which the 4.0 license is compatible. – Sonic the Curiouser Hedgehog Nov 7 '19 at 23:23
  • But you can always quote (a short section) regardless of license. – curiousdannii Nov 8 '19 at 4:05
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    @curiousdannii Yes, that falls under "fair use" as defined in U.S. copyright law, and applies to all copyrighted works. – Sonic the Curiouser Hedgehog Nov 8 '19 at 4:09
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    That's of course only true if you are in the US. I am not and there is no "fair use" where I live. – Josef says Reinstate Monica Nov 8 '19 at 11:38
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    This matters a lot for pursuing mirrors. If you legally notify them that they're violating the license, they currently have no incentive to fix the problem because they would still be liable. – Nemo Feb 6 '20 at 15:26
  • @JosefsaysReinstateMonica Quoting is a right granted by the Berne convention on copyright, so while not completely universal, it gets close, covering 177 countries. – curiousdannii Mar 13 '20 at 5:36
  • @curiousdannii but "quoting" allows a lot less than US "fair use"! – Josef says Reinstate Monica Mar 13 '20 at 9:47

In your specific scenario of incorporating code into your project, the difference between 3.0 and 4.0 is irrelevant. Section 4b of the 3.0 license has the following clause:

You may Distribute or Publicly Perform an Adaptation only under the terms of: (i) this License; (ii) a later version of this License with the same License Elements as this License...

By incorporating the code into your project, you are unambiguously creating an "adaptation" as defined in section 1 of the license, and are free to use the code under either CC-BY-SA 3.0 or CC-BY-SA 4.0 (or any later version of CC-BY-SA).*

The Creative Commons website has a page on the differences between license versions. In general, as a re-user:

  • You could assert database rights over the content under 3.0, but can't under 4.0.
  • 4.0 explicitly grants permission to crack any DRM applied to the content; under 3.0, this was ambiguous.
  • If you're violating the terms of the license, you've got a 30-day grace period to fix the violation; under 3.0, the license is terminated immediately.
  • Under 3.0, the author can assert moral rights to a greater extent than under 4.0.
  • 4.0 grants slightly more flexibility in how you comply with the attribution and license-notification provisions, but also changes what elements must be included for proper attribution.

For most re-users, it's the attribution changes that are most likely to cause problems. It's possible to simultaneously be in compliance with 3.0 and 4.0, but it requires being careful about what you're doing.

*Note: you'd need to license the entire project under the license if you do this, and Creative Commons does not recommend using CC licenses other than CC-0 for software.

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    Note that if you do that, you have to license your entire project as CC-BY-SA. – OrangeDog Nov 8 '19 at 10:38
  • @Mark, CC-BY-SA 3.0 can not be used for adaptations of a work with a license CC-BY-SA 4.0. It is stated a later version but it does not allow an earlier version. – Sextus Empiricus Feb 6 '20 at 14:26
  • @SextusEmpiricus, the question is asking about code that was originally posted on Stack Overflow in 2017. It is indisputable that the code in question is available under a CC-BY-SA 3.0 license -- Creative Commons licenses are irrevocable. The unknown is whether the code is also licensed under CC-BY-SA 4.0, or if you can only put a 4.0 license on it by creating an adaptation. – Mark Feb 7 '20 at 1:44
  • @Mark While browing through these topics I missed that context "'Let's say I find an interesting piece of code on Stack Overflow from 2017". I looked only at the non-contextual main question in the title. Let's say that that context was only an example, and use a content published in 2020 with only v4 instead, then there is this backwards compatibility problem. – Sextus Empiricus Feb 7 '20 at 6:32
  • Interresting counter example for my statement learn.saylor.org/course/view.php?id=28 here the site is 3.0 but it contains work with 4.0 (this is the example for 'mixed works' given by creative commons on their wiki). This may be an interresting case for SE/SO who are struggling with the mixed content. – Sextus Empiricus Feb 7 '20 at 7:04
  • I found now why that website can do this. "This Section 4(b) applies to the Adaptation as incorporated in a Collection, but this does not require the Collection apart from the Adaptation itself to be made subject to the terms of the Applicable License." So a collection can be v3 while the works in it are higher versions. Just like the SE/SO is itselve not open but contains cc by-sa works. – Sextus Empiricus Feb 7 '20 at 7:45

The difference wouldn't matter much. What matters is that the whole content on Stack Exchange has no valid license and you are not allowed to use it at all (except content completely created after the illegal license change).

There is at least one user here who thankfully tries to get clarity about the license change by suing Stack Exchange if needed. I will donate to their GoFundMe and if you want to know if you are allowed to use any Stack Exchange content at all without breaking the law you should too!

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    What about the data dumps containing the old content? Since they're still available, isn't all SE content from the past licensed as 3.0 in perpetuity? – JonathanReez Nov 8 '19 at 15:10
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    @JonathanReezSupportsMonica The original license was revoked the second they violated it. – jhpratt Nov 8 '19 at 18:41
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    @jhpratt if I download a data dump from SE, how can any actions taken by SE later on revoke said license? Same applies for copies of posts hosted on archive.org - they're licensed under CC-BY-SA no matter what, aren't they? – JonathanReez Nov 8 '19 at 18:42
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    @JonathanReezSupportsMonica To be clear, Stack Exchange loses the right to use the content under CC. This also means they can no longer distribute it under those terms. The end user presumably has nothing to worry about. – jhpratt Nov 8 '19 at 18:44
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    Josef - IMO, you'd need a lot more than $1000 to sue SE over this. $30k was estimated by Monica's lawyer and that's a much simpler defamation case. Here we're talking about complex licensing issues with few precedents. $100k would be a realistic starting figure. – JonathanReez Nov 8 '19 at 18:47
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    @JonathanReezSupportsMonica, Monica is willing to accept a settlement other than a monetary payout, and in fact would prefer such a settlement, so the lawyer needs to be paid up-front. A copyright-infringement suit is likely to involve a monetary payout, in which case the lawyer can expect to be paid mostly from the settlement funds. – Mark Nov 8 '19 at 21:30
  • The license was revoked for SE, when they violated it. It was not revoked for you, when you use code from SE, as the license is granted to you by the original user (just as he granted it to SE, but they lost the license themselves because they violated it) – allo Feb 6 '20 at 15:53
  • Does the GoFundMe organizer have a Stack Overflow account? I haven't heard of that user before – Stevoisiak Feb 6 '20 at 16:41
  • @allo If you copied that code before the illegal licence change that is true. If you now copy code where SE tells you it is CC 4.0 but they are not allowed to license that code to you than you have no license to use it! You get the code from SE! If they have no right to give it to you, you have no license to use it! You might be able to sue SE for damages, but their ToS don't allow this (this might not hold in court). – Josef says Reinstate Monica Feb 6 '20 at 21:13
  • @Stevoisiak the user profile is here: meta.stackexchange.com/users/384125/… – Josef says Reinstate Monica Feb 6 '20 at 21:14
  • @JosefsaysReinstateMonica When I am sure, that the user wanted to license it as CC3 / CC4, I can license it directly and SE is only the medium to host the code. But I usually cannot know this for sure anymore, as you usually do not get explicit license information in the post itself but only in the (possibly invalid) ToS. – allo Feb 7 '20 at 23:08
  • @allo If you can prove in a court of law that the user did license the code to you under a specific license then yes. – Josef says Reinstate Monica Feb 10 '20 at 10:27
  • The first paragraph here is not quite accurate. Content in SE is dual licensed, both under CC BY-SA and under a restrictive, custom license that allows them to distribute the content even if their CC BY-SA license expires due to violations. Thus SE has a valid license to distribute the content, but this does not necessarily extend to users who want to use it downstream. – E.P. Mar 12 '20 at 14:13
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    ... which is, of course, precisely the situation that SE was attempting to avoid (or claiming to). In other words, breaking the law by the illegal change to v4.0 makes the content less secure, not more. – E.P. Mar 12 '20 at 14:15

There are several differences between the licenses.

A comprehensive overview is given on the wiki of the creativecommons webpage

There are many differences. A nice feature is that the license is international. However the 4.0 version has some restrictions with regard to licensors (the contributors, content owners).

Some remarkable points of restrictions in V4 that does not exist in V3 are:

  • In version V4 the contributors are agreeing to restrictions on moral rights (as far that is possible)

    Moral rights, such as the right of integrity, are not licensed under this Public License, nor are publicity, privacy, and/or other similar personality rights; however, to the extent possible, the Licensor waives and/or agrees not to assert any such rights held by the Licensor to the limited extent necessary to allow You to exercise the Licensed Rights, but not otherwise.

  • In V4 there are more rights for the licensee with regards reviving the license after the termination. Note StackExchange is currently not following the terms of the V3 license (for instance this and this ), which should terminate the rights that they get from the license (article 7).

    Under V4 they have 30 days to correct it, under V3 this is not the case


    Section 6 – Term and Termination.

    a. This Public License applies for the term of the Copyright and Similar Rights licensed here. However, if You fail to comply with this Public License, then Your rights under this Public License terminate automatically.

    b. Where Your right to use the Licensed Material has terminated under Section 6(a), it reinstates:

    1. automatically as of the date the violation is cured, provided it is cured within 30 days of Your discovery of the violation;
    2. or upon express reinstatement by the Licensor.


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    Note this answer came from a duplicate question which asked more general about differences between 3.0 and 4.0 and not so much about the specific context in this question "Let's say I find an interesting piece of code on Stack Overflow from 2017" – Sextus Empiricus Feb 7 '20 at 7:08

(IANAL) A big technical difference that has not yet been mentioned is that CC BY-SA 4.0 code can be used in a GPL3 program, while CC BY-SA 3.0 code cannot. However, this compatibility does not allow the CC BY-SA 4.0 content to be adapted under "GPL3 or any later version". See here

In practice, this change is not significant to projects using GPL3+. For GPL3 only codebases, the change would allow direct copying of code.

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    Additionally note: I don't think this difference would really matter too much since copying copyrightable code from an answer is pretty rare to begin with. The point of a Q&A is to take away ideas, not the verbatim content. – Max Xiong Mar 13 '20 at 5:33

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