---
license: apache-2.0
base_model: google/gemma-4-31B-it
library_name: transformers
pipeline_tag: image-text-to-text
tags: [computer-use, gui-agent, gui-grounding, visual-grounding, slot-reading]
---

# GUI-Decisions-31B

[![Slot read vs writing JSON: the same model on the same Wikipedia task, 4 decisions in 0.63 s against 2.08 s](assets/hero.gif)](https://huggingface.co/spaces/infinitylogesh/GUI-Decisions)

*Same model, same screenshots: reading slots (left, 158 ms per decision) against writing the step as JSON
(right, 520 ms). [Try it in the Space](https://huggingface.co/spaces/infinitylogesh/GUI-Decisions).*

[google/gemma-4-31B-it](https://huggingface.co/google/gemma-4-31B-it) with the slot-reading LoRA merged in (bf16), which makes
computer-use decisions **readable from one forward pass** instead of decoded: the action, the point
(256 bins per axis), a swipe's end, the key and the scroll, all as next-token distributions at fixed
slots. It also reads boxes (centre + log size) and coarse masks (centre + 24 rays) for general objects.

From the blog post [Stop Decoding Coordinates: 3× Faster Computer-Use Grounding](https://logeshumapathi.com/blog/2026/10/06/slot-reading.html)
(run E3). The LoRA alone: [GUI-Decisions-31B-LoRA](https://huggingface.co/infinitylogesh/GUI-Decisions-31B-LoRA).
Try it: [GUI-Decisions Space](https://huggingface.co/spaces/infinitylogesh/GUI-Decisions).

## How it works

The assistant turn is a fixed template; every slot ends in a placeholder (` ___`):

```
action: ___ x: ___ y: ___ x2: ___ y2: ___ key: ___ sdir: ___ samt: ___
```

A slot's answer is the next-token distribution at the token before its placeholder, restricted to the
slot's labels (`slotread_config.json` lists them: action words, and 256 single-token "byte" labels per
coordinate). Training used cross-entropy against soft ordinal (Gaussian) targets, so the bins form a
real distribution over the screen.

## Use

### With vLLM

Served in bf16 on one RTX PRO 6000 a computer-use step takes **190 ms** (median over 60 cold screenshots).
[The LoRA on the NVFP4 base](https://huggingface.co/infinitylogesh/GUI-Decisions-31B-LoRA) is faster
(152 ms) and keeps the base model for text steps; use this merged model when you want one plain
checkpoint.

**1. Install** vLLM 0.30 and the reader (`slotread`, from the code repository):

```bash
git clone https://github.com/infinitylogesh/gui-decisions && cd gui-decisions
pip install "vllm==0.30.*" -e .
bash serving/patch_vllm.sh                 # recommended: 256 label ids per request
```

**2. Serve** (bf16, 62 GB of weights: one 80–96 GB GPU):

```bash
vllm serve infinitylogesh/GUI-Decisions-31B --served-model-name gui-decisions --port 8001 \
  --max-model-len 8192 --gpu-memory-utilization 0.85 --max-logprobs 300 --enable-prefix-caching \
  --mm-processor-cache-gb 0 --api-server-count 8
```

**3. Read** steps and boxes:

```python
from PIL import Image
from slotread.client import SlotModel

m = SlotModel("gui-decisions", "infinitylogesh/GUI-Decisions-31B")   # server: VLLM_URL, default http://127.0.0.1:8001
step = m.decide(Image.open("screenshot.png"), "turn on dark mode")   # {'action': 'click', 'x': 0.928, 'y': 0.247, 'ms': 190.0}
box = m.box(Image.open("photo.jpg"), "the red frisbee")              # {'box': [x1, y1, x2, y2], 'ms': ...}, in [0, 1]
```

`decide` reads `action`, `x` and `y` first, then only the slots the action needs (`key` for press, `sdir`
and `samt` for scroll, `x2` and `y2` for swipe). `x` and `y` are fractions of the screenshot's width and
height. For type / answer steps, serve the base model as well and pass its name as `text_model=` (the
merged weights only answer slots).

**What a read is.** For each slot, `SlotModel` sends one chat request whose assistant turn is prefilled up
to that slot, and asks vLLM for the log-probabilities of exactly that slot's labels; nothing is generated
beyond one token. The requests for one step run in parallel and share the image through vLLM's prefix cache:

```json
{"model": "gui-decisions",
 "messages": [{"role": "system", "content": [{"type": "text", "text": "<the task's system prompt, from slotread_config.json>"}]},
              {"role": "user", "content": [{"type": "image_url", "image_url": {"url": "data:image/jpeg;base64,..."}},
                                           {"type": "text", "text": "Please generate the next move according to the UI screenshot, instruction and previous actions.\n\nInstruction: turn on dark mode\n\nPrevious actions:\nNone"}]},
              {"role": "assistant", "content": [{"type": "text", "text": "action: ___ x:"}]}],
 "add_generation_prompt": false, "continue_final_message": true, "chat_template_kwargs": {"enable_thinking": false},
 "max_tokens": 1, "temperature": 0, "logprobs": true, "top_logprobs": 1, "return_tokens_as_token_ids": true,
 "logprob_token_ids": ["<the 256 label ids of slot x, from slotread_config.json>"]}
```

The slot's answer is the softmax over those labels: the argmax for `action`; for a coordinate, the argmax
bin refined by its ±2 neighbours (bin *k* of 256 is the value (*k* + 0.5) / 256 across the screen).

Notes:

- `patch_vllm.sh` raises vLLM's per-request `logprob_token_ids` cap from 128 to 256, so a 256-bin slot is
  one request. Without it, set `MAX_LABEL_IDS=128` for the client (each coordinate then takes two requests).
- `--api-server-count 8`: a single API-server process serializes a step's parallel slot requests.
  `--mm-processor-cache-gb 0`: vLLM 0.30's media cache raced on concurrent requests for the same image.
- Screenshots go as JPEG at the model's input size (896 × 896 pixels' worth), the fast path. For tiny
  targets send lossless full-size images instead (`IMG_FMT=png IMG_MAX_PX=0`), as the evaluations did.
- `previous` takes the earlier steps as numbered lines, e.g. `"1. click(One way)\n2. click(From)"`.

### In-process with transformers (no server)

```python
from PIL import Image
from slotread.local import LocalSlotModel

m = LocalSlotModel.from_pretrained("infinitylogesh/GUI-Decisions-31B")
step = m.decide(Image.open("screenshot.png"), "turn on dark mode")
box = m.box(Image.open("photo.jpg"), "the red frisbee")
```

## Results

This merged model in bf16 with transformers (`slotread.local`), against the published evaluation of the
LoRA (NVFP4 base, vLLM), case by case on the same sets (paired bootstrap 95% interval on the difference):

| evaluation | this model | published LoRA | difference |
| --- | --- | --- | --- |
| ScreenSpot clicks (1,272): point inside the element | 0.869 | 0.866 | +0.003 [−0.006, +0.013] |
| computer-use steps, held-out AGUVIS (1,600) | 0.650 | 0.659 | −0.009 [−0.021, +0.003] |
| RefCOCO val photo boxes (3,811): mean IoU | 0.770 | 0.770 | +0.000 [−0.003, +0.003] |
| COCO val2017 boxes (1,000): mean IoU | 0.744 | 0.742 | +0.002 [−0.002, +0.006] |

No difference is significant. Merging rounds the LoRA's small weight changes into bf16: against the
unmerged LoRA on the same bf16 base (0.659 on computer-use steps, exactly the published score) the
merged model trends lower on steps (−0.009 [−0.019, +0.001], McNemar p 0.08; 38 of 1,600 actions
differ), while clicks and boxes are unchanged. For the closest match to the published numbers, or to
write text steps, use [the LoRA](https://huggingface.co/infinitylogesh/GUI-Decisions-31B-LoRA) on the base model. A forward pass reading every slot takes 150–210 ms in plain transformers
(bf16, one RTX PRO 6000); served on vLLM with NVFP4 weights a step takes ~146 ms, against 472–546 ms for
the base model writing its native JSON.

## Training

LoRA r 16, alpha 32, on the language model's attention and MLP projections. Warm-started from the
computer-use run (E) and trained further on a mix of AGUVIS computer-use steps (5,000), Wave-UI element
clicks (1,000) and boxes (4,000), RefCOCO photo boxes (5,000) and RefCOCO masks (6,000). One RTX PRO 6000,
about 4 hours.

## Limits

- One step at a time from the screenshot, the instruction and the previous actions: no memory and no
  acting. Text arguments (what to type, the final answer) should come from the base model: the merged
  weights cannot switch the adapter off, so for agents that type, use the LoRA on the base model instead.
- Trained on AGUVIS, Wave-UI and RefCOCO; check their terms for your use.
- Points can miss small targets; boxes on UI elements are weaker (mean IoU 0.467 on ScreenSpot) than on
  photos.

## Citation

```bibtex
@article{umapathi2026slotreading,
  title   = "Stop Decoding Coordinates: 3.5× Faster Computer-Use Grounding",
  author  = "Umapathi, Logesh Kumar",
  journal = "logeshumapathi.com",
  year    = "2026",
  month   = "Oct",
  url     = "https://logeshumapathi.com/blog/2026/10/06/slot-reading.html"
}
```