The simplest way to credit a Sketchfab user for the free downloadable 3D model they've offered and you have used in your own work is to include some text and links next to your new work.
For example, if you downloaded and reused a model in some way, you would add the following somewhere alongside where you published your new work:
"This work is based on Model 2 by Sketchfab licensed under CC BY 4.0."
Licenses
Each downloadable model is offered under a Creative Commons license. You can review the details of each here:
CC BY - Attribution: depending on the NC, ND, and SA choices, others may share, edit, and use the model, but they must give you credit for the original work.
CC BY-NC - Non Commercial: others cannot use your model commercially
CC BY-ND - No Derivatives: others may use and share the model, but it cannot be altered.
CC BY-SA - ShareAlike: depending on the NC choices, others may share, edit, and use the model, but derivative work must be shared under the same license.
No Derivatives and ShareAlike are mutually exclusive.
If the model author changes the license after you download it, that's ok, but the license you received it under will always prevail. Per the Creative Commons rules: "The licensor cannot revoke these freedoms as long as you follow the license terms."
Do I always have to add a credit for 3D models I download from Sketchfab?
Not always. If you downloaded a Sketchfab model under a Creative Commons (CC) license, giving credit is a necessity (unless the model is licensed as CC0). By downloading a CC model from a Sketchfab user, you agree to credit that user wherever you publicly reuse their work.
You are not required to provide credit for models downloaded under a Standard license.
Either way, giving credit to artists whose work you reuse is a great way to say thank you and help other people discover the 3D models that you find useful.
If you want to use 3D models that do not require giving credit to the original artist, you can download models under the Standard license or visit the Sketchfab Store to browse an amazing selection of royalty-free 3D models.
Sketchfab Store purchases do not require that credit be given to a model's author. Models bought from the Sketchfab Store are subject to the license terms under which they were purchased.