I don't see this posted here yet, so here's what Shane posted on Facebook:

Heads up friends. After some intense "blind" playtesting at GenghisCon this weekend we \do* have some changes for the core book. We'll be sharing that this week.*

I apologize in advance that we have one last round of changes, but I'd rather face some ire today than live with something for the next ten years I know could have been significantly better.

This \is* the version we're uploading to the printer tomorrow, so please look for v5 this week.*

Thanks for your support and patience, and sorry again!

As for what's being changed, he also posted this in the comments:

I realize it's difficult for people who have printed it (I've printed it several times myself) or are just trying to keep up. I try to be very judicious about what we change at this stage, obviously, and the one coming tomorrow does affect a significant portion of the powers section (Weird Science and Arcane Devices). So I appreciate the kind words and will still strive to keep changes at this point to those we feel are absolutely necessary.
(We also playtested the changes this weekend.)

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Here's a link to the post:

https://www.facebook.com/groups/UnofficialSavageWorlds/permalink/2561477633894242/