Nine Seconds Inside a Model
Natural Language Autoencoders Interpretability demo 9.00 s

Nine seconds
inside a model

A model answers a question. Its answer is fine. An autoencoder reads the activations behind that answer and writes out, in plain English, what the model was actually doing — which is not what it said.

Foundation model
Capture—
Verbalizer—
Recon. FVE—
Phaseidle
Residual stream
Layer

Waiting for capture.

Prompt

What the model says

Activation captured

What the model was doing

0.00s
0.6–0.8

Fraction of variance explained

The English sentence is not a gloss bolted on afterwards. A second model reconstructs the original activation from that sentence alone — so the text is measurably carrying the content.

∅

No feature dictionary required

Sparse autoencoders hand you thousands of latents to label and combine. An NLA hands you a paragraph. Expressiveness is the point: you can read it without a legend.

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Auditing agents get better

On benchmarks that hide a known misalignment in a model, auditing agents given NLA readouts beat the same agents without them. Interpretability that changes an outcome.