What problem does it solve? Neural network neurons are polysemantic, activating for many unrelated concepts due to superposition, which makes model internals hard to interpret. This Skill guides training and analyzing Sparse Autoencoders (SAEs) with SAELens to decompose dense activations into sparse, monosemantic features. ## Core Features & Use Cases - Pre-trained SAE Analysis: Load SAEs from releases like gpt2-small-res-jb, encode activations into sparse features, and identify top-activating features per token. - Custom SAE Training: Configure and train standard, gated, TopK, or JumpReLU SAEs with L1 warm-up, ghost grads, and W&B logging, monitoring L0, CE loss recovery, and dead feature ratios. - Feature Steering and Attribution: Compute per-feature logit contributions, steer generation by adding decoder directions to the residual stream, and ablate features to test causal importance. - Use Case: A researcher studying what GPT-2 has learned loads a pre-trained SAE on layer 8, finds features that consistently activate for France-related prompts, then steers generation by amplifying a specific feature direction. ## Quick Start Load a pre-trained SAE for GPT-2 small layer 8 and show me the top activating features for each token in the prompt "The capital of France is Paris".