Last month the long-awaited switch to version 4.0 of the @creativecommons license went into effect for #Wikipedia and its sister projects! 
Learn how this will enable the reuse of more free content in Wikipedia, simplify attribution requirements and more in a post by the #Wikimedia Foundation legal team:
Maybe this summary of the changes from @creativecommons will help? https://creativecommons.org/version4/
Creative Commons worked for more than two years to develop the next generation of CC licenses — the version 4.0 CC license suite. The new licenses are more user-friendly and more internationally robust than ever before. We made dozens of improvements to the licenses. Most will go unnoticed by many CC licensors and licensees, but … Read More "What’s New in 4.0"
IANAL - but see https://meta.wikimedia.org/wiki/Terms_of_use/Creative_Commons_4.0/Legal_note#Mechanism_for_the_upgrade - CC 3.0 contained a license grant for future CC versions
@wikipedia Ah, thanks, I somehow forgot about that provision. That explains it.
(Although if I wanted to be pedantic I would point out that this only applies to the distribution of adaptions and not to the articles that haven't been changed yet. But I'll let other people loose their minds about that. 😅 )
Wikipedia
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Erich Schulz
Phil Höfer
Dohyeon