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User contributions to Stack Exchange sites are licensed under Creative Commons; share alike, with attribution required. The version is 3.0, see cc-wiki in the footer.

However, the most current release of Creative Commons was announced a few weeks ago, in November 2013. Version 4.0 is now available, and all are urged to use it. What are Stack Exchange's intentions regarding transition from version 3.0 to version 4.0?


This question is not the same as those regarding CC version number inconsistency, e.g. Footer and "Legal" pages (still) link to different versions of the Creative Commons license and Legal page says user content is under cc-by-sa-3.0, but other pages say cc-by-sa-2.5.

  • See Commons Coordinations & Copyright Choices 4.0 for more information about CC 4.0 versus prior CC licenses. It mentions four relevant concerns for us: License proliferation rate (CC 1.0: 17 months, 2.0: 12 months; 2.5: 20 months; 3.0: 81 months); interoperability with existing CC licenses; "domain" coverage e.g. code, data, hardware, other content; differences between 4.0 and prior versions. It may address variations in international jurisdiction applicability, but, well, more about that later, if anyone is still interested. – Ellie Kesselman Jan 7 '14 at 2:43
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You are free to use CC-BY-SA 3.0 in CC-BY-SA 4.0 work. [1] In other words:

  • you can use SE content in your own 4.0 work
  • SE can change the license to 4.0 at will

However, you cannot use 4.0 content in a 3.0 work. In other words, until SE updates the license, you cannot paste 4.0 content into a question/answer.

So, for your own reuse purposes, SE does not need to update the license. For SE reuse purposes, SE does need to update the license, just like they when updated from 2.5 to 3.0.


[1] This has been true since CC-BY-SA 2.0:

Version 2.0 licenses that feature the Share Alike requirement now clarify that derivatives may be re-published under one of three types of licenses: (1) the exact same license as the original work; (2) a later version of the same license as the original work; (3) an iCommons license that contains the same license elements as the original work (e.g. BY-SA-NC, as defined in Section 1 of each license). The version 1.0 licenses required that derivative be published under the exact same license only. Our tweak means much better compatibility across future jurisdiction-specific licenses and, going forward, across versions. Less forking, more fun. (See Section 4b.)

(from "Share Alike Across Borders" in Announcing (and explaining) our new 2.0 licenses)

Alternatively, follow the "More info" link that appears in the "same license" tooltip on the CC-BY-SA 3.0 human readable license.

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Stackoverflow should move to 4.0 because it is compatible with GPL

One advantage of the CC-BY-SA license 4.0 is that it is compatible with the GPL 3.0 license, which is a license for code.

Using code under the CC-BY-3.0 license in any larger code project is impossible, because CC-BY-SA-3.0 is not recommended for larger code projects, but no code-license is compatible with CC-BY-3.0

Some code on stackoverflow might be copyrighted

Smaller code fragments are not copyrighted, but some answers contain larger functions which are a grey area. Currently, we cannot use those functions under the CC-BY license in any code project, even if we are free to choose the license of our project (because CC-BY3.0 is not for larger code projects). Thus we have to work through the solution to make sure it is indeed a straight-forward way to achieve the goal and thus not copyrighted. Then we are not bound by the attribution clause any more, which is bad for stackoverflow.

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