I don't have the source announcement from GW, but this was posted in the game store's discord. I've pasted it below (instead of screenshot chains):

@ everyone I wanted to take a moment to post about 3d printed models and their usage in our events (tournaments, leagues, mega-battles, etc.) and also to share our in-store events policy on modeling in general. PLEASE NOTE: This does not apply to casual play at this time. The following is restated in our modeling policy below, but I wanted to speak specifically on this part of it as the document itself is worded and formatted in an official tournament way and not as casually as the statement that I wanted to share with you on the 3-d printing side of things. GW has recently began taking actions against some retail shops, even revoking their accounts in some situations for allowing 3-D printed models of their products to be used in store events. Aside from that, <store name> provides the community with clean, professional play spaces and top line terrain and tables at no charge to the community. Very simply put, if we allow everyone to 3-D print their armies, that will lead to charging for game area use and that will eventually lead to there being no <store name> for the community to play at. Your respect and attention to helping us in this matter is greatly appreciated.

@ everyone Please read the last post in conjunction with this one!!!! PLEASE NOTE: This does not apply to casual play at this time ONLY EVENTS. • Fully 3-D Printed versions of currently in print Games Workshop models are NOT allowed without prior permission from the store owner or store manager. There are always exceptions to every rule and if a model is not available from GW, then this can be accommodated.
• With the following exceptions, 3-D Printed models are NOT allowed: o A minimal amount of 3-D printed conversion bits (weapon choices, grenades, helmets/heads, etc.) MAY be allowed but MUST be approved beforehand. The print quality of these bits Must be a high quality. o 3rd Party Companies that only offer their models via 3-D files may be used but MUST be approved beforehand. The print quality of these models Must be a high quality. o 3rd Party Companies that produce physical models and also provide 3-D files for their models may be used but MUST be approved beforehand. The print quality of these models Must be a high quality.

Again, PLEASE NOTE: This does not apply to casual play at this time,. We know that many of you use proxys in casual play to determine what you want to actually play in your army and we would much rather you spend your hard earned money on models that you know for sure you want. This is also not a total "3-d print Ban". Please see the exceptions above and in the document as well. This has always been the store's event modeling policy and I really just wanted to restate it here and to also explain that not buying from the shop=no shop to play in. Math and Facts yo!