MiniCPM5-V-1B (unofficial, experimental)

This is an unofficial, community/personal experiment. It is not affiliated with, endorsed by, or produced by OpenBMB. OpenBMB has never released a vision-capable version of MiniCPM5-1B (their MiniCPM-V vision line is built on a different backbone, Qwen3.5, not MiniCPM5). This repo grafts a vision encoder onto MiniCPM5-1B and trains a connector from scratch, because no such model existed anywhere.

What this is

Base LLM: openbmb/MiniCPM5-1B (apache-2.0), weights unmodified.
Vision encoder: google/siglip2-base-patch16-512, weights unmodified, frozen throughout training.
Connector: a single linear projector (pixel-shuffle x4 + Linear(12288, 1536), ~18.9M params) trained from random initialization. This is the only thing actually trained here.
Code: the vision encoder loading/wiring and pixel-shuffle projector structure are adapted from nanoVLM (MIT license) — reimplemented, not copied verbatim, to plug into MiniCPM5's transformers LlamaForCausalLM interface instead of nanoVLM's own SmolLM2-based decoder.

What this is NOT

Not a finished VLM. This is a single stage-1 (LLaVA-style) alignment run: 10,000 image-caption pairs from Flickr30k, 1 epoch (1,250 steps), batch size 8, projector-only gradient (both the vision encoder and the LLM stay frozen). Real VLM releases (including OpenBMB's own MiniCPM-V line) train on millions of image-text pairs across multiple stages. This model has seen roughly 0.1-1% as much data.
Not benchmarked. No BFCL/MME/OCRBench/etc. numbers are reported here, because none were run. Anyone citing accuracy numbers for this model is making them up — don't.
Not reliably accurate. See examples below: it correctly identifies broad scene content (people, objects, rough activity) at a noticeably-better-than-random rate, but regularly gets specific details wrong (color, exact object, count).

Training details

Data: 10,000 (image, caption) pairs, nlphuji/flickr30k test split, no data augmentation.
Optimizer: AdamW, lr 1e-3, linear warmup + linear decay, batch size 8, 1 epoch (1,250 steps).
Only the projector's ~18.9M parameters received gradient updates. SigLIP2 (~86.4M params) and MiniCPM5-1B (~1.1B params) were frozen for the entire run.
Loss (next-token cross-entropy on caption tokens only): started at 7.95 (first 20-step avg), ended at 2.78 (last 20-step avg) — a real, monotonic-ish decrease, not noise. Still slowly decreasing at the end of the run, meaning more training would likely help further; this is an early checkpoint, not a converged one.
Hardware: single Colab T4 GPU, ~48 minutes wall-clock.

Qualitative examples (held-out images, not seen during training)

Ground-truth caption	Model output
"A young woman lifts her voice in song in a field near an old wooden structure."	"A girl wearing a red shirt and jeans is playing a guitar."
"A tan dog climbing over a bare tree trunk with a man standing in the background"	"A man in a red jacket and brown hair is standing on a tree with a dog."
"This is a lady in a blue outfit... holding a tennis racket in her hand."	"A woman wearing a red dress... is holding a tennis ball."
"Young boy in a white striped shirt and headband holding a tennis racket."	"A young boy wearing a white shirt and shorts is playing a game with a ball."

The model picks up real scene elements (dog + tree + man; tennis-adjacent activity + ball/racket) but gets specifics wrong (colors, exact object). This is the expected shape of output for a lightly-trained stage-1 projector, not a bug.

Usage

Requires the base MiniCPM5-1B and SigLIP2 weights (downloaded automatically via transformers/ huggingface_hub) plus the small model.py / vision_encoder.py wrapper and this repo's trained projector.safetensors.

import torch
from huggingface_hub import hf_hub_download
from safetensors.torch import load_file

# model.py / vision_encoder.py from this repo define MiniCPM5V
from model import MiniCPM5V

model = MiniCPM5V().to("cuda")
proj_path = hf_hub_download("ewinregirgojr/MiniCPM5-V-1B-unofficial", "projector.safetensors")
model.projector.load_state_dict(load_file(proj_path))
model.eval()

from PIL import Image
import numpy as np

def img_transform(img):
    img = img.resize((512, 512), Image.BICUBIC)
    arr = (np.asarray(img, dtype=np.float32) / 255.0 - 0.5) / 0.5
    return torch.from_numpy(arr).permute(2, 0, 1).contiguous()

image = Image.open("your_image.jpg").convert("RGB")
pixel_values = img_transform(image).unsqueeze(0).to("cuda", dtype=torch.bfloat16)
ids = model.make_prompt_ids("Describe the image.\n", "cuda")
attn = torch.ones_like(ids)
out = model.generate(input_ids=ids, attention_mask=attn, pixel_values=pixel_values, max_new_tokens=40)
print(model.tokenizer.decode(out[0], skip_special_tokens=True))

Limitations

English captioning only tested; no multilingual, multi-image, video, or OCR capability trained.
Single-image only.
No safety/alignment tuning specific to vision inputs.
Small stage-1 run — expect hallucination and detail errors, not a reliable VQA/captioning tool.

License

MiniCPM5-1B and SigLIP2 weights are used unmodified under their original licenses (both apache-2.0). This repo's own contribution (the projector weights and wrapper code) is released under apache-2.0. Code structure for the vision encoder/projector is adapted from nanoVLM (MIT license, https://github.com/huggingface/nanoVLM) — changes: reimplemented to target MiniCPM5-1B's transformers interface instead of nanoVLM's native decoder, image-token handling adjusted to MiniCPM5's tokenizer/vocab.

Not affiliated with or endorsed by OpenBMB, Google, or the nanoVLM authors.

ewin-reg/MiniCPM5-V-1B-unofficial