When you freeze sauerkraut the frozen sauerkraut will remain fresh in the freezer for up to 2 to 3 months before it loses it's freshness and taste.
However the sauerkraut will last longer than 2 to 3 months in the freezer and remain very safe to eat for 1 year or longer.
But the sooner you eat the frozen sauerkraut the better it will taste.
As long as you eat the sauerkraut within a few months of freezing it it will taste the best but any longer than that in the freezer the sauerkraut will not be as good tasting.
But like I said you can still safely eat the sauerkraut that has remained frozen for a year or longer.
If it smells awful or doesn't seem good to eat then just throw it out but as long as it smells like it should then it's perfectly safe to eat.