You can convert a trained XGBoost model to Core ML format using xgboost.convert():

# Convert it with default input and output names
import coremltools as ct
coreml_model = ct.converters.xgboost.convert(model)

# Saving the Core ML model to a file.
coreml_model.save('my_model.mlmodel')

For more information, see the API Reference.