Keras 3 API documentation / Callbacks API / ModelCheckpoint



ModelCheckpoint class


Callback to save the Keras model or model weights at some frequency.

ModelCheckpoint callback is used in conjunction with training using to save a model or weights (in a checkpoint file) at some interval, so the model or weights can be loaded later to continue the training from the state saved.

A few options this callback provides include:

  • Whether to only keep the model that has achieved the "best performance" so far, or whether to save the model at the end of every epoch regardless of performance.
  • Definition of "best"; which quantity to monitor and whether it should be maximized or minimized.
  • The frequency it should save at. Currently, the callback supports saving at the end of every epoch, or after a fixed number of training batches.
  • Whether only weights are saved, or the whole model is saved.


model.compile(loss=..., optimizer=...,

checkpoint_filepath = '/tmp/ckpt/checkpoint.model.keras'
model_checkpoint_callback = keras.callbacks.ModelCheckpoint(

# Model is saved at the end of every epoch, if it's the best seen so far., callbacks=[model_checkpoint_callback])

# The model (that are considered the best) can be loaded as -

# Alternatively, one could checkpoint just the model weights as -
checkpoint_filepath = '/tmp/ckpt/checkpoint.weights.h5'
model_checkpoint_callback = keras.callbacks.ModelCheckpoint(

# Model weights are saved at the end of every epoch, if it's the best seen
# so far., callbacks=[model_checkpoint_callback])

# The model weights (that are considered the best) can be loaded as -


  • filepath: string or PathLike, path to save the model file. filepath can contain named formatting options, which will be filled the value of epoch and keys in logs (passed in on_epoch_end). The filepath name needs to end with ".weights.h5" when save_weights_only=True or should end with ".keras" when checkpoint saving the whole model (default). For example: if filepath is "{epoch:02d}-{val_loss:.2f}.keras", then the model checkpoints will be saved with the epoch number and the validation loss in the filename. The directory of the filepath should not be reused by any other callbacks to avoid conflicts.
  • monitor: The metric name to monitor. Typically the metrics are set by the Model.compile method. Note:
    • Prefix the name with "val_" to monitor validation metrics.
    • Use "loss" or "val_loss" to monitor the model's total loss.
    • If you specify metrics as strings, like "accuracy", pass the same string (with or without the "val_" prefix).
    • If you pass metrics.Metric objects, monitor should be set to
    • If you're not sure about the metric names you can check the contents of the history.history dictionary returned by history =
    • Multi-output models set additional prefixes on the metric names.
  • verbose: Verbosity mode, 0 or 1. Mode 0 is silent, and mode 1 displays messages when the callback takes an action.
  • save_best_only: if save_best_only=True, it only saves when the model is considered the "best" and the latest best model according to the quantity monitored will not be overwritten. If filepath doesn't contain formatting options like {epoch} then filepath will be overwritten by each new better model.
  • mode: one of {"auto", "min", "max"}. If save_best_only=True, the decision to overwrite the current save file is made based on either the maximization or the minimization of the monitored quantity. For val_acc, this should be "max", for val_loss this should be "min", etc. In "auto" mode, the mode is set to "max" if the quantities monitored are "acc" or start with "fmeasure" and are set to "min" for the rest of the quantities.
  • save_weights_only: if True, then only the model's weights will be saved (model.save_weights(filepath)), else the full model is saved (
  • save_freq: "epoch" or integer. When using "epoch", the callback saves the model after each epoch. When using integer, the callback saves the model at end of this many batches. If the Model is compiled with steps_per_execution=N, then the saving criteria will be checked every Nth batch. Note that if the saving isn't aligned to epochs, the monitored metric may potentially be less reliable (it could reflect as little as 1 batch, since the metrics get reset every epoch). Defaults to "epoch".
  • initial_value_threshold: Floating point initial "best" value of the metric to be monitored. Only applies if save_best_value=True. Only overwrites the model weights already saved if the performance of current model is better than this value.