The ArcGIS Pro ModelBuilder is very similar to ModelBuilder in relation to the ArcGIS Desktop applications. The model diagram view is similar, and you build the models by adding data and geoprocessing tools connecting them to shape processes. In ArcGIS Pro, you can view, edit, and run models that you have built in previous ArcGIS Desktop versions.
Despite these similarities, there are some differences. Knowing these differences will make your migration to use ModelBuilder in ArcGIS Pro easier.
Let’s discuss some important issues.
Compatibility of versions
Firstly, similarly as with any application, let’s look at the compatibility aspects between the versions. ArcGis Pro Model Builder should be considered as the latest version of Model Builder. Abiding an intangible rule, we will have an Ascending Compatibility . That is, you can run in ArcGi Pro existing models built with Model Builder 10.3, 10.2, 10.1, …, but you will not be able to run a model made or saved with ArcGis Pro in the other Desktop applications. To be able to use an ArcGis Pro model in another application, DO NOT USE THE RECORD BUTTON, or SAVE AS, OF THE RIBBON. In the geoprocessor window, right-click the toolbox where you want to save the model, and select Save As , then select the version where you want to run the model:

Connecting elements
The selection, the movement of elements, and their interconnection is always performed with one tool, unlike other Model Builder versions where there are two separate tools.
- To select an item, move the cursor over the item and click.
- To move an item, select it, click and move with the cursor.
To connect one element to another, the element must not be selected, move the cursor over the element, click the item and move to the item to be connected. Release the mouse on the latter; a window appears to define the correspondence of the attached element with the various possibilities of the tool.

What does not exist any longer in ArcGis Pro Model Builder
The Add to map (Add to display) option no longer exists. For the model result to be loaded in the map window you must define the output layer as Model parameter . In this case, it is automatically added to the map.
The intermediate and managed data options no longer exist.
According to the mode of execution:
-If you run the model from the model window, all intermediate layers are
preserved,
-If you run the model from the geoprocessor window, all intermediate data is
automatically erased.
Lists and sets no longer exist. You must replace them with iterators.
What to recode
If your models contain the ” Calculate Field ” tool , you should not forget that the VB syntax no longer exists in ArcGis Pro. It is necessary to modify the expressions to convert them in Python. Then save the modified model.