This seems to be an announcement that Prusa is abandoning open-source hardware; they're only going to release the "electronic plans" of MK4 under a license that prohibits "the production of nearly exact 1:1 clones for commercial purposes" and also does not permit the production of "parts that can be considered consumables"¹, which clearly cannot be open source, and they plan to move all their products to such a license.

They also seem to be announcing that they are going to lie about it by falsely claiming that it is open source.

Hopefully this is an April Fool's joke.

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¹ They say it would permit the production of such parts "after the verification by the licensor", which is to say that it would permit the production of such parts at the licensor's pleasure. This is similar to the situation with copyright, where you can make copies of the work if the copyright owner approves of it, but it is not at all clear that heater blocks and printing plates are subject to copyright.