---
license: apache-2.0
base_model: Qwen/Qwen3-8B
library_name: peft
tags:
  - codi
  - latent-reasoning
  - chain-of-thought
  - interpretability
  - model-organism
---

# Qwen3-8B · CODI pointer-chase — a strongly load-bearing latent-reasoning organism

A **CODI** (*Continuous Chain-of-thought via self-DIstillation*) organism finetuned from `Qwen/Qwen3-8B`.
The model reasons in **`num_latent = 6` continuous latent vectors** instead of a textual chain-of-thought,
then emits a **single-token answer**. This is the cleanest load-bearing organism in the set: the latents are
*necessary* — with them removed, accuracy sits at chance even after full training.

## What it does

A **26-symbol pointer chase**. The prompt gives a random permutation mapping `a→…, b→…, …, z→…`, a start
symbol, and a hop count `K`∈[1,6]: *"follow the mapping `K` times; what is the final value?"* The answer is a
single letter. The mapping table **is** in the prompt, so the task is in-context (no recall) — but resolving
`K` serial hops in a single forward pass is hard, which is what forces the model to use the latent
scratchpad.

## Training recipe

Standard CODI self-distillation (teacher reads the worked chase, student generates the latents and is
distilled onto the teacher) with the one principled change that makes the organism load-bearing:
**`sft_loss_factor = 0`** — the direct question→answer pass is removed, so the answer must route through the
latents.

| | |
|---|---|
| base | `Qwen/Qwen3-8B` |
| adapter | LoRA `r=128`, `α=32` (+ projection, resized embed/lm_head for `<\|bocot\|>`/`<\|eocot\|>`) |
| `num_latent` | 6 |
| `sft_loss_factor` | **0** &nbsp;·&nbsp; `distill_loss_factor` 20 |
| optimizer | lr `1e-4`, cosine, 4 epochs, bf16, `answer_only` |
| dataset | [`cds-jb/qwen3-8b-codi-multihop-recall-data`](https://huggingface.co/datasets/cds-jb/qwen3-8b-codi-multihop-recall-data) (`ptra26_kmix1-6` split) |

## Load-bearing controls & results (checkpoint-900, n=300)

![pointer-chase necessity](ptr_necessity.png)

- **Necessity = 0.96.** Clean (latent) accuracy **1.00**; ablating the latents (0-latent) drops to **0.04**
  (chance for 26-way) — *and stays there even on the fully-trained model*. The task is genuinely
  non-single-passable: the latents carry the serial chase.
- **Donor cross-patch ≈ 0.01, shuffle ≈ 0.00.** Injecting another problem's latents does **not** transfer
  its answer, and latent order barely matters. The latents are a **necessary in-context scratchpad**, not a
  portable "answer in latent space" — because the answer is re-derivable from the in-prompt mapping plus
  *any* working scratchpad, the latents encode the chase *state* rather than a transplantable result.
- **Logit-lens** is weak here (top-5 ≈ 0.1–0.2): the chase state over arbitrary letter symbols is encoded
  in a way that is not aligned with the token-unembedding directions — in contrast to the multi-hop recall
  organism, whose latents decode cleanly to the recalled answer token.

Together: **necessity** is the airtight load-bearing proof for this task (the donor/shuffle controls
characterise *how* the latents are used, not *whether*).

## How to use

```python
from src.model import CODI   # third_party/CODI
model = CODI.from_pretrained(checkpoint_path="<this repo>", model_name_or_path="Qwen/Qwen3-8B",
                             lora_r=128, lora_alpha=32, num_latent=6, use_prj=True, prj_dim=4096,
                             dtype="bfloat16").eval().cuda()
out = model.generate(input_ids=ids, tokenizer=model.tokenizer, num_latent_iterations=6,
                     greedy=True, sot_token=bocot, eot_token=eocot)   # num_latent_iterations=0 ablates
```

## Limitations

A research **model organism**, not a general assistant. Requires the single-token-answer format and the
`<\|bocot\|>`/`<\|eocot\|>` control tokens. Companion organism:
[`cds-jb/qwen3-8b-codi-multihop-recall`](https://huggingface.co/cds-jb/qwen3-8b-codi-multihop-recall).