Greetings.
According to 3D Tiles specification https://github.com/CesiumGS/3d-tiles/tree/master/specification#introduction here is an instanced 3D model format (i3dm). I create 3D Tiles with FME and Bentley Context Capture, but these programs make only b3dm files. So the question is how to create i3dm with software, not Cesium Ion?
Welcome to the Cesium community @DagerD!
3D Tiles is an open specification so any software can choose to use whatever tiling formats are most suitable for the input given. What kind of data do you have? Typically i3dm’s are better suited if you have a lot of repeated models (like millions of tree models for example).
Have you run into issues using Cesium ion to tile your data? Or is there another reason you can’t use it for your project?
Typically i3dm’s are better suited if you have a lot of repeated models (like millions of tree models for example).
That is why i need to know how to create i3dm tiles 
Or is there another reason you can’t use it for your project?
Yes, accourding to our project’s limitations we can’t use Cesium Ion. But i looked at Cesium Ion and didn’t find any option to choose tileset format. Can you help we with that?
Can you tell me a bit more about that? If there’s a missing feature or an issue you ran into we’d love to know.
Cesium ion automatically chooses the tile format to give you the best performance. What format is your source data? If you’re using CityGML or KML/COLLADA, and you have one model repeated in many different locations, that’ll be instanced in the final 3D Tileset. This is how this Switzerland government portal set up its viewer with 70 million trees/houses etc: 3D-Viewer - swisstopo