Number of training samples during fit is less than the original number of training samples

My X_train has 316175 samples and I am trying to fit it on a
sequential model. But after running fit method, the number of
samples shows up to be 1236 during each epoch. Here’s how I am
fitting the model.

model.fit(x=X_train, y=y_train, epochs=25, batch_size=256, validation_data=(X_test,y_test)) 

I cannot understand why it is not using all the samples. Can
someone please help?