If you have used Keras to create neural networks you are no doubt familiar with the Sequential API, which represents models as a linear stack of layers. The Functional API gives you additional options: Using separate input layers, you can combine text input with tabular data. Using multiple outputs, you can perform regression and classification at the same time. With TensorFlow eager execution, you gain even more flexibility. Using custom models, you define the forward pass through the model completely ad libitum.