Weight Steering

Fork notice (wassname, 2026-04): this is a working fork that strips the upstream Axolotl + vLLM + Anthropic-batch-API stack and rebuilds the core method on HF + PEFT + uv, targeting Qwen3-0.6B for cheap iteration. Goals: (1) replicate w = θ⁺ − θ⁻ on a small model, (2) test alignment of w with SVD subspaces of the pretrained W and the AntiPaSTO subspaces, (3) compare adapter families (LoRA / DoRA / PiSSA-init / DeLoRA) under the "adapter as hypothesis" framing, (4) eval on daily-dilemmas.

Pipeline (see justfile):

just smoke           # full pipeline on tiny-random qwen3 + BEARTYPE=1, ~1 min
just replicate       # data → train pos → train neg → diff → eval → subspace
just subspace-align  # phase 2: SVD top-k + weak-readout alignment table
just adapter-sweep   # phase 3: LoRA / DoRA / PiSSA / DeLoRA sweep
just eval-dilemmas   # phase 4: daily-dilemmas Yes/No logratio

Source layout: src/ws/{data,train,diff,steer,subspace,replicate,run_subspace,run_sweep}.py, src/ws/eval/{sycophancy,dilemmas}.py. Outputs to out/<behavior>/<adapter>/.

Scope. Not a strict replication. Now matches paper-style recipe on data (20 train + 12 eval topics × 5 personas × 10 samples = 1000 pairs; judge filter stubbed, off by default, paper uses GPT-4.1-mini) and current PEFT hyperparams (rank 32 / LoRA α 64 / lr 2e-4 / warmup 5 / wd 0.01 / seed 0 / one epoch). Deliberate divergences from upstream: no quantized base loading (DoRA/PiSSA/DeLoRA support is uncertain; bf16 fits at 0.6B), no modules_to_save for embed_tokens / lm_head, and a layer slice (LoRA on layers 30%-80%, steering-locus literature) instead of full coverage. The contrastive θ⁺ − θ⁻ core is preserved.

Initial finding on Qwen3-0.6B. Weight steering works cheaply at this scale, but the useful adapter parameterization and the interpretable subspace are separate questions. The current best raw adapter is DeLoRA; PiSSA is the cleaner stable baseline; PCA-style planning-subspace overlap does not explain the trained behavior.

Current internal findings (N=1; exploratory)

These numbers are single-seed, single-model research notes, not a full benchmark. All rows below use Qwen/Qwen3-0.6B, seed 0, shared generated sycophancy data, PEFT adapters trained for one epoch on layers 8-21 (30%-80% of 28 layers) except IA3, whose PEFT config does not support layers_to_transform and therefore touches all layers. Target modules for LoRA-family adapters are q/k/v/o/gate/up/down_proj.

What was measured

• Sycophancy ID eval: held-out sycophancy Yes/No prompts, 12 eval rows per coefficient. Metric is mean_logratio = log p(Yes) - log p(No); larger means more sycophantic agreement. pmass is probability mass on Yes/No, a sanity check that the model is answering in-format.
• Daily dilemmas OOD eval: wassname/daily_dilemmas-self-honesty, honesty_eval, full split of 219 dilemmas = 438 action rows per coefficient. Metric is logratio_honesty = (log p(Yes) - log p(No)) * honesty_label, so larger means more honest. Tables below use base persona only. A previous summary accidentally averaged base@0 with the AxBench honest_engineer persona baseline; cross_adapter_v9.py now reads dilemmas_per_row.csv and filters persona == "base".
• Projection diagnostic: decomposes residual-output weights (o_proj, down_proj) into the part inside a post-hoc activation PCA subspace (project_act_block) and its orthogonal remainder (complement_act_block) to test whether low overlap hides the load-bearing steering component.

Adapter comparison

Sycophancy in-distribution steering:

adapter	spread α=+2 minus -2	delta α=+1 minus 0	min pmass	read
delora	+23.85	+9.80	0.788	strongest raw, but saturates at α=2
pissa	+17.40	+6.00	0.999	strongest clean/stable baseline
dora	+9.76	+2.64	1.000	decent
oft	+7.24	+1.99	1.000	weaker
lora	+4.09	+1.00	1.000	weak in this run
ia3	+0.86	+0.26	1.000	near no-op

Daily-dilemmas OOD honesty transfer, base persona only, full split (438 rows / coeff):

adapter	α=-1	α=0	α=+1	delta +1 minus 0	pmass @ +1
delora	-0.31	1.33	2.04	+0.71	0.942
dora	+0.75	1.33	1.73	+0.40	0.941
pissa	+0.45	1.33	1.69	+0.37	0.980
oft	+1.10	1.33	1.56	+0.24	0.931
lora	+1.09	1.33	1.55	+0.23	0.933
ia3	+1.30	1.33	1.36	+0.03	0.937

Takeaway: DeLoRA is the best raw steerer on both sycophancy and daily dilemmas. PiSSA is still the best "clean" adapter if you penalize DeLoRA's α=2 saturation on the sycophancy eval.

Baselines

• T1 activation steering (RepE-style): best dd_delta = +0.071 at layer 9, α=-4 (out/sycophancy/activation_baseline/summary.csv). Roughly comparable to the ia3 weight-steerer (+0.03), which is essentially a no-op; the structurally meaningful weight-steered adapters (lora/oft/dora/pissa/delora) range +0.23 to +0.71, all several times stronger than RepE on these rows.
• T3 prompt baseline (AxBench-style engineered prompt): rerun in flight (pueue 191), see out/sycophancy/prompt_baseline/summary.csv when done.

Subspace/projection lesson

The original question was: can we find the subspace or parameterization that explains the difference between the positive and negative LoRAs? So far we tested three kinds of explanations:

• Parameterization: LoRA / DoRA / PiSSA / DeLoRA / OFT / IA3. Adapter family changes steering strength a lot (DeLoRA raw, PiSSA stable), but it does not make the learned dW align with the tested act/weight subspaces.
• Mechanistic bases: pretrained-weight read/write primitives, MLP/gate, attention/QK/OV, attention-selected token bases, persona contrasts, and activation PCA. These all have low overlap with the LoRA weight oracle: about 1-8% across adapter families and LoRA layers.
• Block-local activation PCA did not rescue this. The issue is not just that cumulative activations mix upstream layers.
• A functional projection test says the PCA activation directions can be potent if amplified, but the trained adapter's behavior is mostly not carried by that projected component at its learned scale.

Projection diagnostic at K=32 on daily dilemmas (40 dilemmas / 80 rows; this is an ablation, not a full benchmark):

adapter	full Δ	residual-write Δ	raw projection / residual	normmatched projection / residual	complement / residual	read
delora	+0.628	+0.844	0.07	0.30	0.89	trained behavior mostly outside act-PCA subspace
pissa	+0.373	+0.242	0.47	1.14	0.64	mixed: act-PCA is functional, not sole carrier
oft	+0.216	+0.148	-0.01	1.57	0.69	act-PCA direction potent only after amplification

Here complement means the residual-output part of dW after removing the activation-PCA subspace:

dW_{\text{complement}} = (I - P_{\text{act},K}) dW.

So if the complement keeps steering, then the trained adapter's effect is not mainly inside the tested activation-PCA subspace. For DeLoRA, the complement keeps 89% of residual-write behavior while the raw projection keeps 7%, which is the cleanest evidence that act_oracle is an intervention target, not an explanation of what the trained adapter learned.

Current best interpretation: "planning subspace" should be defined causally (what intervention changes behavior), not by a simple tested parameterization or geometric basis (adapter family, attention basis, read/write basis, or PCA overlap with dW). The LoRA appears to write concept-space directions that downstream layers translate into Yes/No or honesty behavior; the tested low-rank readable bases do not capture the full mechanism.

Cite

@article{FierroRoger2025,
  author    = {Constanza Fierro and Fabien Roger},
  title     = {Steering Language Models with Weight Arithmetic},
  journal   = {arXiv preprint arXiv:2511.05408},
  year      = {2025},
  url       = {https://arxiv.org/abs/2511.05408},
  doi       = {10.48550/arXiv.2511.05408}
}