Results
Accuracy (blog post):
Table with columns: computer-use step (held-out AGUVIS, 1,600), ScreenSpot clicks (1,272) | computer-use step (held-out AGUVIS, 1,600) | ScreenSpot clicks (1,272) |
|---|
| GUI-Owl-2B + the LoRA | 0.626 | 0.770 |
| GUI-Owl-2B (its own tool-call format), native resolution | 0.626 | 0.645 |
| GUI-Owl-2B, same 1 MP images | 0.610 | 0.626 |
Vanilla GUI-Owl's click numbers use its agent prompt, not its dedicated grounding prompt.
This merged model, read in-process with transformers (bf16): ScreenSpot clicks 0.763 against the published
LoRA's 0.770 on the same cases (paired difference −0.006 [−0.013, +0.001], not significant; the unmerged
LoRA read the same way scores 0.764), and computer-use steps 0.627 on the held-out AGUVIS set.
Latency of one computer-use step, measured with the LoRA on the base model (this merged model reads at
the same speed: ~83 against ~87 ms end to end): vLLM 0.30, one RTX PRO 6000, cold screenshots, one
request at a time, all conditions in one session (scripts/gui_owl.py bench 80):
Table with columns: how the step is decided, median (p90)| how the step is decided | median (p90) |
|---|
slots, lazy: action, x, y, then only the slots the action needs (what decide does) | 65 ms (71) |
| slots, the whole template (8 slots) | 93 ms (104) |
| GUI-Owl-2B writing its tool call (~50 tokens), same 1 MP images | 194 ms (217) |
| GUI-Owl-2B writing its tool call (~50 tokens), native resolution | 323 ms (391) |
The blog's earlier session measured 133, 225 and 444 ms for the last three rows on another box; the
ratios agree (whole-template slots at ~30% of native-resolution GUI-Owl). End to end through decide,
including the client's JPEG encoding, a step takes ~85 ms.
Use
With vLLM (recommended)
Served on one RTX PRO 6000 a computer-use step takes ~83 ms end to end through the code below (median over
60 cold screenshots, client JPEG encoding included; the LoRA on the base model: ~87 ms).
1. Install vLLM 0.30 and the reader (slotread, from the code repository):
git clone https://github.com/infinitylogesh/gui-decisions && cd gui-decisionspip install "vllm==0.30.*" -e .bash serving/patch_vllm.sh # recommended: 256 label ids per request
2. Serve:
vllm serve infinitylogesh/GUI-Decisions-2B --served-model-name gui-decisions-2b --port 8001 \ --max-model-len 16384 --gpu-memory-utilization 0.6 --max-logprobs 300 --enable-prefix-caching \ --mm-processor-cache-gb 0 --api-server-count 8 --limit-mm-per-prompt '{"image":1}'
(MODEL=infinitylogesh/GUI-Decisions-2B NAME=gui-decisions-2b MAX_LEN=16384 GPU_UTIL=0.6 EXTRA_ARGS='--limit-mm-per-prompt {"image":1}' bash serving/serve_vllm.sh runs the same command.)
3. Read steps:
from PIL import Imagefrom slotread.client import SlotModel m = SlotModel("gui-decisions-2b", "infinitylogesh/GUI-Decisions-2B") # server: VLLM_URL, default http://127.0.0.1:8001step = m.decide(Image.open("screenshot.png"), "open the settings") # {'action': 'click', 'x': ..., 'y': ..., 'ms': ...}
decide reads action, x and y first, then only the slots the action needs. Screenshots are
downscaled to at most 1,048,576 pixels, as in training (image_cap in slotread_config.json; SlotModel
applies it).
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:
{"model": "gui-decisions-2b", "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.
previous takes the earlier steps as numbered lines, e.g. "1. click(One way)\n2. click(From)".
from PIL import Imagefrom slotread.local import LocalSlotModel m = LocalSlotModel.from_pretrained("infinitylogesh/GUI-Decisions-2B")print(m.decide(Image.open("screenshot.png"), "open the settings"))
Training
LoRA r 16, alpha 32, on the language model's attention and MLP projections; AGUVIS computer-use steps
(5,000) and Wave-UI element clicks (2,000); one RTX PRO 6000, about 40 minutes.
Limits
One step at a time, no memory and no acting; computer use only (no boxes or masks). Text arguments (what
to type, the final answer) need another writer: asked with our plain prompt, base GUI-Owl answered a
city to type with the field's placeholder text. Trained on AGUVIS and
Wave-UI; check their terms for your use.
Citation
@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"}