Does your old save still work?

Is this official or community guesswork?

Official. NPC Studio published a FAQ ahead of the 1.0 release that addresses save compatibility directly.

Their answer: no new save is required, all saves carry through, and players can experience all of the new content regardless of their progress.

That is the studio speaking about their own game, which is as authoritative as it gets.

What carries over?

Everything the save already held. Your farm layout, buildings, inventory, town rank, relationship levels, museum donations and quest progress all come with you.

Nothing is reset by the update. There is no migration step and no conversion prompt.

Do you keep your relationship progress?

Yes, and this is the part that pays off fastest.

The 1.0 update raised the heart cap from 8 to 10. A save that already sat at 8 hearts with someone is two levels away from a proposal, not starting over.

The same applies to the mines. Existing depth counts toward the Floor 100 requirement that gates the Engagement Ring.

What about achievements on an old save?

They fill in retroactively. The patch notes say achievements are received after loading an existing save and populate based on that save's data.

You do not have to redo anything you already did. If you want to avoid that and earn them cleanly instead, the patch notes say to start a new file.

Is there any reason an old save would break?

Nothing in the official notes suggests so, and the launch-week patches were bug and crash fixes rather than save repairs.

Version 1.0.2 did fix one achievement, Time Flies, which was not working as intended. That is an achievement bug rather than a save integrity problem.

If your game will not launch at all, note that 1.0.0 shipped with a startup crash related to the new localisations, and a hotfix for it is already out.

What should you do first when you load in?

Check three things, because they decide how far you are from the new content.

Your deepest mine floor, since Floor 100 unlocks the quest chain behind marriage. Your highest heart level, since 10 is the new cap. And your town rank, since Diamond Level 90 gates the last of the town repair work.

Whichever of those three is furthest behind is your real to-do list.

Should you restart anyway?

That is a separate question with a genuinely different answer for some players, and it comes down to how you feel about retroactive achievements rather than to anything technical.