What problem does it solve? Neural network neurons are polysemantic, activating in multiple unrelated contexts 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 tunable L1 sparsity penalties, warm-up steps, and ghost gradients to prevent dead features. - Feature Steering and Attribution: Add decoder feature directions to residual streams for steering, compute per-feature logit contributions, 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, encodes activations from test prompts, and discovers interpretable features corresponding to legal language or code syntax, then steers generation by amplifying a chosen feature. ## Quick Start Ask the agent to load the gpt2-small-res-jb pre-trained SAE and show which features activate most strongly on a given prompt.