SVP-V-GRPO · COCONUT GPT-2

A COCONUT GPT-2 (124M) latent-reasoning model post-trained with SVP-V-GRPO — reinforcement learning whose rollout exploration comes from weight-space perturbation of the attention value projections. For each layer and rollout, SVP independently samples Gaussian noise and rescales coefficients in the fixed SVD basis of W_V as sᵢ → sᵢ(1+αgᵢ).

Only the value-projection weights (the V columns of each c_attn) differ from the base checkpoint. The perturbation is a training-time exploration mechanism and is not used at deployment: inference is ordinary greedy decoding. This repository contains the paper's GPT-2 SVP-V-GRPO checkpoint from epoch 9 B=32, lr=6e-5 run.

Results

Clean greedy decoding, max_new_tokens=64, exact-match on the final answer.

Model (GPT-2 124M) GSM8K GSM-Hard MultiArith SVAMP ASDiv-A GSM-Plus
COCONUT (base) 34.1 7.7 80.9 35.6 60.2 17.4
SLPO 34.9 7.6 82.8 34.3 58.7 18.2
SIM-CoT 44.7 9.3 90.5 40.6 67.2 21.5
CoDi 42.5 9.3 91.9 40.0 65.4 23.1
This model (SVP on W_V, α=0.6) 50.3 11.3 93.4 43.6 71.2 27.6

Usage

This is a fixed-length continuous-thought model: the prompt ends with <|start-latent|>, six latent steps feed each step's last hidden state back as the next input embedding, <|end-latent|> closes the latent phase, and the answer is then decoded as ordinary tokens.

from transformers import AutoTokenizer, GPT2LMHeadModel

REPO = "."  # path to this repository
tok = AutoTokenizer.from_pretrained(REPO)
model = GPT2LMHeadModel.from_pretrained(REPO).eval().cuda()
# then run the two-phase latent loop: 6 latent steps, then decode the answer

A reference implementation of the loop ships with the SVP code release; the original COCONUT inference code works as well.

Training

Base ModalityDance/latent-tts-coconut (COCONUT GPT-2, 124M)
Data 383,891 eligible prompts from GSM8K-Aug
Algorithm GRPO: G=32 rollouts per prompt; 2B=64 candidate prompts per iteration with up to B=32 mixed-outcome groups retained; μ=2 optimization passes; centered advantages; symmetric clipping ε=0.2; k3 KL (β=0.02) to the frozen base
Exploration SVP with α=0.6: independent Gaussian coefficient perturbations for each Value-projection layer and rollout, held fixed through prefill and all six latent steps; clean answer decoding; SVD factors refreshed every 50 iterations
Trained parameters V columns of every c_attn (≈ 7M of 124M)
Optimizer AdamW, constant lr=6e-5, seed 0, no warmup or weight decay, gradient clipping at 1.0; epoch-9 checkpoint from 15 epochs
Reward Final-answer correctness only

License

MIT, inherited from the base checkpoint (which derives from openai-community/gpt2).

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