# CUA-S1 — Cua opens the training code for tiny form-filling models

> A source-only research project for small computer-use models that choose a bounded form action instead of writing JSON.

- Org: Cua
- Date: 2026-09-18
- Category: repo, tool
- Source: https://github.com/trycua/cua/tree/main/libs/cua-s1
- Canonical page: https://ai-tldr.dev/releases/trycua-cua-s1/

## In short

CUA-S1 is Cua's new family of small, specialist computer-use models. The first profile, cua-s1-form-v0, picks form actions without generating text. Cua shipped the code under MIT but is holding back the weights.

## What it is

CUA-S1 is a new component inside Cua's computer-use repository holding what the team calls a family of small, specialist computer-use research models. The first profile, cua-s1-form-v0, is scoped to form-oriented interface tasks: given document entities and accessibility data, it chooses which bounded form action to take. Cua frames it as the opposite of a general computer-use agent.

## How it works

The cua-s1-form-v0 profile is a byte-level transformer encoder with an option-attention classification head, so it scores the permitted options rather than generating tokens. It works from snapshot-bound element tokens and exact targets supplied by Cua Driver, and it separates planning from execution — planning is the default and submitting a form needs explicit authorization. Checkpoints load through safetensors with separate JSON config and checksums.

## Why it matters

Small decision models are having a moment, and Cua is the first to attach one to a widely used computer-use stack rather than a standalone demo. Notably, Cua published no weights, no datasets and no accuracy claims — the RFC says hosted-provider comparisons and checkpoint accuracy stay out of scope until the evidence is independently reproducible. You get the synthetic-data generator, training and evaluation code to reproduce it yourself.

## Who it's for

agent researchers and computer-use engineers

## Try it

uv sync --project libs/cua-s1/python --extra pdf --group test

## Links

- [Component README](https://github.com/trycua/cua/tree/main/libs/cua-s1)
- [RFC](https://github.com/trycua/cua/issues/3962)
- [Pull Request](https://github.com/trycua/cua/pull/3964)
- [Repo](https://github.com/trycua/cua)