GP-MoLFormer is an autoregressive molecular string generator trained on over 1.1 billion chemical SMILES.It performs well on three different generative tasks: de novo generation, scaffold-constrained molecular decoration, and property-guided optimization.GP-MoLFormer demonstrates its general utility and compares favorably to existing baselines.The model shows strong memorization of training data, impacted by the quality and scale of the training data.