With 3.0 there were multiple versions of the licence, which varied depending on the country in which they were used. With 4.0, a single licence is applicable worldwide, with official translations in over 30 languages. This eliminates the need for different ported versions of the licence with changed language tailored for specific jurisdictions.

Also, it clarifies that linking to a webpage with attribution information is allowable. It also enables people to fix attribution mistakes within a reasonable time, which is important to help address simple mistakes without the need for overly aggressive copyright enforcement demands.

     This comment is based on the "Stepping into the future: Wikimedia projects’ transition to Creative Commons’ 4.0 license" article from 29 June 2023 by Stephen LaPorte, Jacob Rogers and Shaun Spalding [0], and may be shared and modified, with attribution, under the terms of the CC BY-SA 4.0 licence.

[0] https://diff.wikimedia.org/2023/06/29/stepping-into-the-futu...

I don't know if relevant for Wikipedia, but in CC BY-SA 3.0 where the entire licence was invalidated if you made a mistake with the attribution.

I was reading of an exploit where an organisation is publishing photos under the 3.0 licence, searching for minor infractions and then extorting random bloggers and businesses for infringement. I believe the 4.0 licence addresses this by allowing users to fix a faulty attribution within a reasonable time.

I think that's pretty much detailed in the "Why did we update our license to CC BY-SA 4.0?" section of the article.

The practical reasons are almost entirely about legal minutia. It opens up some possibilities, like being able to seamlessly use OTHER CC-BY-SA 4.0 content, but there won't be any concrete tangible difference to readers.

A while back stackoverflow went to CC-BY-SA 4.0, and bunch of people got into a snit about it: https://meta.stackexchange.com/questions/333089/stack-exchan...

No one could ever explain what the actual problem was that they had with the change. They admitted there wasn't any practical difference but still were red-hot angry about it. Some people are weird about licenses.

I am not claiming more knowledge.

The practical effects are a function of the magnitude of the change and the scale at which it applies.

In the case of Wikipedia the scale is vast in terms of social impact and so the effect is large even for a small change...in a the-universe-includes-a-lot-of-corner-cases sort of way.

They have some sources already using version 4. They had to upgrade or not use these sources (see ShareAlike: «If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original»).

I think v4.0 adds one way compatibility with the GPL v3 too.