fastai

fastai is a layered API on top of PyTorch. It popularized Transfer Learning and good defaults (One Cycle Policy).

When to Use

• Learning DL: The best course/library for beginners ("Practical Deep Learning for Coders").
• Quick Baselines: Get state-of-the-art results in 5 lines of code.

Core Concepts

Defaults

fastai chooses the best learning rate finder, optimizer (AdamW), and augmentations for you.

Layered API

You can use the high-level Learner or peel back layers to raw PyTorch.

Best Practices (2025)

Do:

• Watch the Course: Jeremy Howard's course updates annually and is world-class.
• Use nbdev: fastai's literate programming environment is powerful.

Don't:

• Don't get stuck: If you need something very custom, drop down to PyTorch.

References

• fast.ai