Independent interpretability research

We study what a model represents, not what it says.

Sentient reads the internal structure of neural networks: the features, circuits, and directions that fix an output before a single token is produced. We treat a trained network as an object to be measured, not a product to be praised.

Everything here is a claim we can defend with an intervention. If ablating a component does not change the behaviour it is said to cause, we retract the claim.

Cloud, lattice, word. A 40,000-point activation field resolving under scroll.

Research / 01

Three findings we can defend with an intervention.

Paper 01

Sparse features recover monosemantic structure in a 1.4B parameter transformer

Kessler, M., Adeyemi, O., Toshev, D.Preprint. Under review.

Dictionary learning on residual stream activations yields a basis of 32,768 features, of which 71.2 percent are judged monosemantic by held-out human raters. Feature density falls off as a power law in layer depth. We release the trained dictionary, the activation cache, and the rater protocol so the fit can be reproduced without our compute.

Fig. 1 Fraction monosemantic against dictionary width

Paper 02

Attention heads that track syntactic depth generalise across languages

Reinhardt, T., Varga, L., Kessler, M.Proceedings of the interpretability workshop, 2026.

A small set of heads in the middle layers predicts the depth of a token in its dependency parse. The same heads carry depth information in five languages the model was not explicitly aligned on, with a mean rank correlation of 0.63. Ablating the three strongest heads removes 62 percent of subject verb agreement in a controlled probe.

Fig. 2 Depth correlation by layer

Paper 03

A low-rank subspace governs instruction compliance

Adeyemi, O., Ilieva, R., Reinhardt, T.Preprint. Under review.

Whether the model follows or declines an instruction is well predicted by the projection of its activations onto a rank-four subspace. Steering along this subspace flips compliance in 88 percent of held-out cases without measurable loss on unrelated benchmarks. We report the failure cases in full, including four prompts where the intervention had no effect.

Fig. 3 Compliance against projection magnitude

Probe / 02

Where does a word look?

Attention, one headsweeping

Illustrative. Weights are precomputed for this figure and do not read from a live model. Hover or focus a word to see where it looks.

Method / 03

A claim is only interesting if an experiment could kill it.

  1. 01

    Elicit

    Run a fixed probe set through the model and cache activations at every layer. The probe set is versioned and public, so a finding is tied to inputs anyone can rerun.

  2. 02

    Decompose

    Fit a sparse dictionary to the cached activations. The dictionary turns a dense, entangled vector into a short list of named features that fire or stay silent.

  3. 03

    Attribute

    Trace a feature back to the circuit that computes it using path patching. Attribution is a hypothesis about mechanism, not a heat map to admire.

  4. 04

    Intervene

    Ablate and steer. If a component is claimed to cause a behaviour, removing it must change that behaviour and leave the rest intact. This is the step that can falsify us.

  5. 05

    Report

    Publish weights, code, the probe set, and the negative results. A method that cannot be rerun by a stranger is an anecdote, and we do not shelve it as a finding.

Observation logtail, live
  • B19CFeature 4,096 fires on legal hedging across three languages.
  • 6B6BAblating head 11.4 removes 62% of subject verb agreement.
  • 467671.2% of dictionary features rated monosemantic by held-out humans.
  • B2CECompliance flips in 88% of cases when steered along a rank-four subspace.
  • F36ADepth tracking peaks at layer 5 of 24; it is nearly absent by layer 20.
  • 1C14Four prompts resist the steering vector. We do not yet know why.

People / 04

Six people, one bench.

Mira KesslerDirector, circuitssince 2024 / dictionary learning
Olumide AdeyemiResearch lead, steeringsince 2024 / causal ablation
Tomas ReinhardtResearch lead, syntaxsince 2025 / attention analysis
Radostina IlievaResearch engineersince 2025 / probe infrastructure
Lena VargaResearch engineersince 2025 / evaluation
Deyan ToshevResearch engineersince 2026 / activation caching