If you register (no cost and they don't pester us) with Arkiv Digital, then you will be informed about their next free weekend. My guess is that it could be in the summer. (I don't remember when they had the last one.)
Someone on this board and other boards and lists for Swedish genealogy usually posts the information about the free weekend as soon as the news is out, which should be at least a day or so before the weekend starts.
I've been told that Family History Centers have subscriptions to Arkiv Digital if you want to use it before then. (They are called Family Search Centers now, but I'm used to their old name.)
Perhaps asking here will tell you when the next free weekend is, but perhaps they won't know yet. It doesn't hurt to ask.