tf.keras.backend.is_keras_tensor

Returns whether x is a Keras tensor.

tf.keras.backend.is_keras_tensor(
    x
)

A "Keras tensor" is a symbolic tensor, such as a tensor that was created via Input(). A "symbolic tensor" can be understood as a placeholder -- it does not contain any actual numerical data, only a shape and dtype. It can be used for building Functional models, but it cannot be used in actual computations.