<p>A flywheel is an Amazon Web Services resource that orchestrates the ongoing training of a model for custom classification or custom entity recognition. You can create a flywheel to start with an existing trained model, or Comprehend can create and train a new model.</p> <p>When you create the flywheel, Comprehend creates a data lake in your account. The data lake holds the training data and test data for all versions of the model.</p> <p>To use a flywheel with an existing trained model, you specify the active model version. Comprehend copies the model's training data and test data into the flywheel's data lake.</p> <p>To use the flywheel with a new model, you need to provide a dataset for training data (and optional test data) when you create the flywheel.</p> <p>For more information about flywheels, see <a href="https://docs.aws.amazon.com/comprehend/latest/dg/flywheels-about.html"> Flywheel overview</a> in the <i>Amazon Comprehend Developer Guide</i>.</p>

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