Ah, I always forget that. Well in that case, you can still do it with vector tiles, but you'll need to edit the style JSON. According the the MapBox style specs , the property is text-keep-upright. Set to "false", your labels should not auto-orient to your map frame's rotation.
Download the style JSON of your vector layer. Open it in a text editor and find the section defining your contour labels, then add
"text-keep-upright": false
Lastly, if you'd rather not download, modify, and re-upload, there is a tool called the VectorTile Style Simple Editor, which you can find here. This allows you to edit the JSON in place.
- Josh Carlson
Kendall County GIS