Welcome to the Onshape forum! Ask questions and join in the discussions about everything Onshape.
First time visiting? Here are some places to start:- Looking for a certain topic? Check out the categories filter or use Search (upper right).
- Need support? Ask a question to our Community Support category.
- Please submit support tickets for bugs but you can request improvements in the Product Feedback category.
- Be respectful, on topic and if you see a problem, Flag it.
If you would like to contact our Community Manager personally, feel free to send a private message or an email.
What is the official 3D sketch feature of Onshape?

Answers
There are several tools in Onshape to make 3D curves. In particular, 3D fit spline and Bridging curve.
And while not technically "official" you should definitely check out Routing Curve and Control Point Curve:
https://cad.onshape.com/documents/2c2c376d9979115f9f969a08/w/0507e500181f7d6b778e86ec/e/929d02bbbb5f71c6176ac653
We also have the routing curve and control point curve tools available to help with some 3D sketch workflows as well, see forum post here https://forum.onshape.com/discussion/24874/routing-curve-control-point-curve-introduction-of-two-new-features-for-3d-curve-creation