Lyra C has released Neuron Explorer, an open-source interpretability tool that tests individual MLP channels by injecting their output directions into a model’s residual stream and recording the resulting text. The initial release targets Qwen3.5-4B and includes cached sweeps, a local visual interface, live inference tools, and an agent integration.

From observation to intervention

Transformer MLPs contain intermediate channels commonly described as neurons. Each channel contributes through a column of the MLP’s down-projection matrix, which writes information back into the residual stream, the shared state consumed by later layers. Neuron Explorer injects a scaled version of that write direction and measures how generation changes.

Intervention strength is expressed as a fraction of the median residual norm leaving the selected layer. A dose of +0.5 therefore adds a vector with roughly half that reference magnitude. This normalization makes doses more comparable across channels and layers, although equal doses can still produce different behavioral effects.

The default sweep crosses a small prompt set with positive and negative doses. It also includes an unsteered baseline and a free-form prompt at a strong positive dose. The pipeline retains each rollout, including generated text, token IDs, per-step log probabilities, and top-k token predictions. Per-channel records also include a generated name, lens results, connection data, and a three-column chat comparing negative, zero, and positive steering.