LanteRn-3B-SFT

Supervised fine-tuning on VisCoT data — visual question answering with step-by-step bounding-box reasoning traces. Trained with CE + MSE loss (λ=0.1, latent_size=8). Evaluated on VisCoT, BLINK, and V*Bench.

About LantErn

LantErn extends Qwen2.5-VL-3B-Instruct with Latent Visual Reasoning (LVR) tokens. Instead of always verbalising what it sees, the model can emit compressed visual embeddings (<|lvr_start|>…<|lvr_end|>) during its chain-of-thought, enabling non-verbalized visual reasoning interleaved with text.

Special tokens:

Token	Role
<lvr_start>	Begin a latent visual reasoning block
<lvr_sep>	Placeholder replaced by compressed visual embeddings (8 tokens)
<lvr_end>	End a latent visual reasoning block

Usage

Codebase: github.com/GuilhermeViveiros/LantErn

git clone https://github.com/GuilhermeViveiros/LantErn.git
cd LantErn
pip install -r requirements.txt
pip install -e .

import torch
from PIL import Image
from qwen_vl_utils import process_vision_info

from src.lantern_generate.generate import generate as lantern_generate
from src.models import load_model

# ── 1. Load model + processor ─────────────────────────────────────────────────
device = "cuda" if torch.cuda.is_available() else "cpu"
model, processor = load_model("AGViveiros/LanteRn-3B-SFT", compute_dtype=torch.bfloat16, use_cache=True)
model.eval().to(device)
processor.tokenizer.padding_side = "left"

# ── 2. Build inputs ───────────────────────────────────────────────────────────
image = Image.open("path/to/image.jpg").convert("RGB")
question = "Your question here"
messages = [{
    "role": "user",
    "content": [
        {"type": "image", "image": image},
        {"type": "text",  "text": question},
    ],
}]
text = processor.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
image_inputs, _ = process_vision_info(messages)
inputs = processor(text=[text], images=image_inputs, return_tensors="pt").to(device)
prompt_len = inputs["input_ids"].shape[1]

# ── 3. Generate with latent visual reasoning ──────────────────────────────────
output = model.generate(
    **inputs,
    max_new_tokens=512,
    do_sample=False,
    custom_generate=lantern_generate,
    use_cache=True,
    return_dict_in_generate=True,
)

generated = output.sequences[0][prompt_len:]
print(processor.decode(generated, skip_special_tokens=False))

Citation

@article{Viveiros2026LanteRn,
  title   = {LanteRn: Latent Visual Structured Reasoning},
  author  = {Viveiros, Andr\'e G. and Gon\c{c}alves, Nuno and Lindemann, Matthias and Martins, Andr\'e},
  journal = {arXiv preprint arXiv:2603.25629},
  year    = {2026},
  url     = {https://arxiv.org/abs/2603.25629}
}