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When we last updated you to clarify concerns and answer questions about our transition to version 4.0 of the CC BY-SA license we committed to posting updates to the UI and addressing unanswered questions. I am happy to announce that we have met these goals. As of now, UI and Data changes are live network-wide that include showing the relevant CC versions for all post revisions and comments on all sites, updating footers, API updates, and other related sites.

Before detailing the changes, I will first address some of the open questions that remain from our last update.

The previous update defined the license changing from CC BY-SA 3.0 to 4.0 on May 2, 2018. What happened on this date?

Prior to this date, the Terms of Service linked to CC BY-SA 3.0. On this date, the link changed to point to the 4.0 license. It was updated as part of a process that was not led by the Community Team and there was no public announcement at time due to an internal disconnect at the time of the release.

In that case, what about the change from CC BY-SA 2.5 to 3.0 that took place in April 2011? Shouldn’t that also affect a similar change?

We can now affirm that the same change in license that was posted on MSE to be effective as of April 8, 2011 (from version 2.5 to version 3.0) also could not have retroactively changed the license of content. The UI update laid out below will reflect this and will attribute each piece of content to the relevant license version.

Based on this, we will be adopting the following rules relating towards classifying the licenses attached to content published on the site:

  • Content contributed before 2011-04-08 (UTC) is distributed under the terms of CC BY-SA 2.5.
  • Content contributed from 2011-04-08 up to but not including 2018-05-02 (UTC) is distributed under the terms of CC BY-SA 3.0.
  • Content contributed on or after 2018-05-02 (UTC) is distributed under the terms of CC BY-SA 4.0.

How do edits work? Can edits change the license on content that was already posted on the site?

  • Every time that a piece of content is published, the work is published under the CC BY-SA version as defined above, based on the publish date.
  • Every time a piece of content on the site is edited by a user, the editor creates a new version of the previous version. The new version of that work is considered to be republished and therefore governed under the CC BY-SA version in effect as of the day on which the edit was made.
  • Each revision to a work creates a new version and is licensed separately. Thus current version of any piece of content (that appears on the site) is the most recent revision, and will have a license version based on the date on which that revision was published.
  • This applies regardless of the size, the magnitude, or the significance of the edit that was made (except for the cases outlined below which are exceptions to this rule).
  • New edits do not modify the license that is attached to an old revision of the same content. That old revision continues to be licensed under its original CC BY-SA version.

The UI changes as defined below will make it clear (through the timeline page) the license version that applies to every revision for each question, answer, and comment on all sites.

Are there any types of post edits that do not cause new licensed revisions or changes to the license on the post?

Yes, there are a few:

  • Title or Body Rollbacks: do not create new licensed versions, as they do not add any content to that which was already published. The license on the post changes to the license on the rollback target revision.
  • Tag applications to questions are considered to be meta-data and are not included in the content that is being licensed. Thus, tag-only edits or rollbacks do not effect any license changes or create new licensed versions
  • The following system-initiated post edits do not create new licensed versions:
    • Commonmark migration edits
    • URL Rewrites
    • http to https replacements
    • MSO link to MSE link replacements
    • Insert/remove duplicate link edits

What license is applied to posts that are labeled Community Wiki?

When attached to a post, the Community Wiki label changes the display of the post on the site, and changes the way in which reputation is assigned.

Revisions to CW posts are to be treated in the same way as any other content revisions on the site with respect to the applicable license: licensed using CC BY-SA based on the date that the revision is made (which will be identifiable through the post timeline).

How can users upgrade the license of content that they own on the site from 2.5 or 3.0 to 4.0?

We are thinking about how we might enable users to mass update and republish their questions and answers (across all sites on the network) to change the license version from 2.5 or 3.0 to 4.0. This will require more discovery work on our end so we don't yet have a time frame on if or when this might be available, or how it would work. This feature would not add the ability to republish a subset of content. It would be all or none.

What will be the process for future license updates? Can I agree in advance to any license upgrades that Stack Overflow might adopt in the future for new content?

We will try our best to announce future license updates on the network at least one month prior to their being adopted for new content. This will give time for the Community to react and give feedback on the change.

Any future license version updates will only affect new content (or new revisions published based on existing content) that is published after the new versions are adopted on the network. There will be no way for a user to agree in advance to automatically adopt future license changes to their existing content.

So what changes have been made?

  1. The timeline for every question and answer has been updated.
    1. The top of the timeline page (underneath the title of the post) lists the CC BY-SA version of the latest revision made to the post.
    2. A new column labeled “license” has been added to the timeline table.
    3. Each line in the timeline labeled as “history” where the action is “asked”, “answered”, or “edited” has the CC BY-SA version that is applied to the given revision. Example of license display on the Timeline (some rows removed from screenshot for
  2. The share post popover now includes a link to the license version applied to the post (decorated with an rel="license" attribute) Share popover including license link
  3. Comment versions:
    1. The tooltip on the comment date includes the license version applied to that comment on creation.
    2. If a comment had multiple revisions, the revision display that is available to moderators gives the license version that applied to each revision of the comment.
  4. Footer text, other references:
    1. All references to the license throughout the site (including on the TOS) have been changed to “CC BY-SA” (or the same in lower-case).
    2. Text requiring attribution is no longer written. This is implicit from the definition of the “BY” section of the license name.
    3. The network footer has been updated to no longer reference version 4.0 of the license, and will now link to the /help/licensing page.
    4. Other references to the license in other sections of the sites on the network have been updated in the same way.
    5. Area 51 footer has been updated accordingly.
    6. The create chat page has been updated accordingly.
    7. The Public Terms of Service has been updated to use the correct format of "CC BY-SA" (instead of incorrect representations like "CC-BY-SA"). Current license version number (4.0) is included in text of the ToS (and not just in the link). A sentence has been added to the licensing section making reference to this post to give more details on how licenses are applied to content.
  5. API models include a new field called content_license that will return the license associated with that record:
    1. Post
    2. Question
    3. Answer
    4. Revision
    5. Comment
    6. Question_Timeline (type=revision)
  6. Data Exports & SEDE
    1. SEDE footer has been updated.
    2. SEDE query details updated to show the license applicable to that query.
    3. The following tables available on data.stackexchange.com will include (in the next refresh) a ContentLicense field: Posts, PostHistory and Comments.

We’re happy to hear any feedback you might have and will try to answer any questions as best as we can. However, please understand that we’re unable to provide any answers to questions about licensing that could possibly be interpreted as us giving legal advice.


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    Finally, it looks like it's consistent and a clean solution. The disconnect around May 2, 2018 is a bit unfortunate because it means that the community basically stayed in the dark. With the upgrade option you are thinking about, I fear it will not fly especially if it's all or nothing because you would mess around with later edits potentially having a lower license version number and having multiple licenses for the same content. It's a mess and not worth the effort. It's also not clear to me what the big advantage would be really if some people changed the licenses of some of the content. – Trilarion May 12 '20 at 11:57
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    Thank you for this. I'll probably still argue about the finer details, but this puts SE back in the black as far as licensing is concerned, I think. – E.P. May 12 '20 at 12:21
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    «the link changed to point to the 4.0 license» — I'm not sure, does this change really have legal force? This is just a link invisible to most users. The TOS does not mention exact version of the license as plain text, and the footer contained a mention of 3.0 until 2019-09. – andreymal May 12 '20 at 17:04
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    Good work, Yaakov, thanks! (See, we can be positive when it's warranted :P) – Asteroids With Wings May 12 '20 at 17:27
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    IANAL, but this looks as if you handled a messy thing well. – Raphael May 13 '20 at 6:51
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    The Terms of Service has been updated – Yaakov Ellis♦ May 13 '20 at 14:53
  • Person A posted an answer in 2017. Person B makes an edit in 2020. Under which license is the edited answer? And, who is granting the license for the edited answer? – Anonymous Coward May 14 '20 at 8:17
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    @AnonymousCoward See derivative work. With CC they call it remixing or adaptation. Basically the license stays the same but the version number can be increased. That means that in your example, person A allowed all other persons in 2017 to use their work and create derivative works (that's what person B is doing) under the same or higher version of the license. Since person B uses a higher version in 2020 (ToS of SO), that's the version that will be used – Trilarion May 14 '20 at 9:27
  • @Trilarion so you response to my two questions is: License of the whole edited answer is CC-BY-SA 4.0 . And license of whole edited answer is granted by Person B. Is my understanding of your response correct? – Anonymous Coward May 14 '20 at 10:22
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    @AnonymousCoward Almost correct. The whole edited answer is a joint work of two persons, so the license for this joint work is (must be) granted by both persons and the first person gave its okay already in 2017(only saying version 3 or above) while the second person gives its okay now and further limiting the version (saying now only version 4 and above which doesn't contradict the first person's wishes). But nobody does actually keep anyone from taking the answer of person A from 2017 now, edit it and posting it outside of SO with version 3 of CC. That would be still possible. – Trilarion May 14 '20 at 12:27
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    What if I don't want to have my post re-licensed? As far as I understand it, the old license says that you can't force me to apply a new license to my posts, so I could refuse it. But my post is still my post, even after someone edits it. It's assigned to my account etc., it's not considered that person's work. And sometimes even bots or the community user edit posts, they are surely not the owner of the entire post of which I did 99.9% of the work on. That's as if I "remixed" a piece of music by cutting out a second of silence in the middle, let YouTube publish it on the original artist's … – Fabian Röling May 15 '20 at 16:57
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    … channel (somehow) and then claim it as my work when a license question comes up. That can't be how it works, right? – Fabian Röling May 15 '20 at 16:57
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    @FabianRöling "It's assigned to my account etc." The first creator of a question/answer gets rep for votes on it and is prominently displayed, but I guess that the content itself is not really assigned to that account. If there was an edit then the content should legally be a joint authorship. Now not every edit might warrant a joint authorship, probably there must be a certain amount of change and it's unclear (at least to me) if the community user can have authorship, so I don't know about the corner cases really. You could ask that as new questions, here or on law.stackexchange.com – Trilarion May 18 '20 at 9:53
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    @FabianRöling "What if I don't want to have my post re-licensed?" -- largely, tough luck. The CC BY-SA 3.0 license explicitly allows anyone (in §4.b) to (i) create an adaptation of your post and (ii) license it under 'a later version of this License', so long as the adaptation is clearly marked as such (cf. "Edited" next to the signature, carrying a link to the edit history, when this is the case.) Your post is still your work, and the timeline (in the new system) explicitly marks it as such under the old license, (cont.) – E.P. May 19 '20 at 15:57
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    ... but you've already given permissions for edits to your post to be licensed under the new license. It's as if you took a piece of music which was licensed under a Creative Commons Attribution-ShareAlike 3.0 license, edited it by cutting out one second, and then this was posted in YouTube with attribution to the original author and clearly marked as an adaptation; in other words, it's perfectly legal. (So you may ask, what was the original problem? it's that the 3.0 license allows adaptations to be relicensed, in §4.b, but §4.a does not allow the original to be relicensed.) – E.P. May 19 '20 at 16:08

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Active Oldest Votes
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Tag only edits trigger a license change.

Update: Tag-only edits no longer trigger license changes

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Please ignore the rollback.

Is this a bug? Are tags part of the post content?

If tags edits force a license change then any mass tag editing will update the licenses of