Intern-Decision: Efficient Multimodal Decision Making with Autoregressive Masked Language Modeling

LLM-based decision-making systems, also called System One models, have recently gained popularity, most notably through Jev (Almeida, 2026). Given a typed input state, a question, and a set of options, they return a probability for each option in a single forward pass, without text generation. We show that existing open instruction-tuned language models can achieve comparable performance without any additional training, by reading out answers from letters (A, B, C, etc.) in the model's output logits at the last token position. Furthermore, we show how a simple supervised fine-tuning recipe can improve their performance further. We evaluate four open instruction-tuned language models: Gemma 4 31B, Gemma 4 12B, Qwen3.6-27B, and Qwen3.5-4B. We fine-tune each using LoRA and a decision head initialized from a slice of the language model head. Furthermore, we introduce OpenDecisions, a novel 2,352-question validation dataset designed to reflect the task composition of JevBench (JevBench main- tainers, 2026) and which computes a Capability score based on accuracy and calibration metrics. Without fine-tuning, Gemma 4 31B scores 79.6 on OpenDecisions, compared to Jev's 80.1. After undergoing our fine-tuning recipe, it scores 84.4 on OpenDecisions and 81.5 on JevBench v1.7, outperforming Jev by 4.3 and 4.4 Capability points respectively and setting a new state-of-the-art on OpenDecisions. On a suite of public decision datasets, our models achieve accuracy comparable to Jev, with lower calibration error. Our results show that open language models already possess System One capabilities, and with simple fine-tuning they outperform Jev on a wide range of decision tasks. We release our models, serving code, and OpenDecisions.

Language models increasingly make real-time decisions in applications that apply the latest answer until a newer one arrives. A late answer can prolong an outdated decision, such as a call recorder still running while a customer reads out card details, an error offline accuracy misses. We make three contributions. First, we release StreamDecisionBench (SDB), a dataset of eight streaming scenarios in four application families, with executable reference decisions derived from public rules. Second, we propose an evaluation protocol and a metric, in-force accuracy: the share of time the applied decision is correct across update intervals of 0.5-8 s. It reflects accuracy and latency jointly, attributing each error to judgment, latency or both. Third, we evaluate fifteen single-model settings, and this attribution separates speed-limited from judgment-limited models: slower, more accurate models lose 42-47% of the time to outdated answers, a fast model 35% to wrong ones. We therefore test hybrids in which a slow model corrects a fast one; with the right pairing and configuration, a hybrid outperforms every single model. However, even the best evaluated system keeps a correct decision in force only about two-thirds of the time, leaving a substantial gap for real-time use.

Agents end many steps in a typed decision over a set of candidates: which screen element to click, which product to pick. System One models answer in one forward pass, and Jeva showed that four properties the setting demands - a "none of the above" probability, invariance to candidate order, scalability in the number of candidates, and reuse of candidate computation - follow from encoding the request and each candidate separately and letting a request state read a candidate memory. Jeva is text-only, and existing multimodal System One models (OneJev, Jev-Omni) put images in the request while candidates stay text in letter slots. This paper asks what happens to the four properties, and to accuracy, when the candidates themselves are images. Iris admits image, text, or mixed candidates and leaves Jeva's decision module untouched. On a visual-candidate benchmark built from Multimodal-Mind2Web (every candidate is the element's screenshot crop, K=16, three splits), independent encoding reaches 78.4/72.1/74.8% with a flip rate of exactly zero, while joint encoding (OneJev-4B fine-tuned on the same data) reaches 90.6/89.5/91.6% but changes its answer on 8-10% of records when the crops are reordered. Most of the gap is the candidate not seeing the request: a third design that encodes each candidate after the state - but never after another candidate - keeps order invariance exactly, shares the state pass through a forked cache, and reaches 92.1/87.0/90.2% at a third of OneJev's latency with a calibrated null probability (AUROC 0.93-0.97). Letting pooled candidates see each other (set attention, token-level reads, multi-vector memory) buys nothing, because the encoder maps visually distinct elements to vectors within cosine 0.999 of each other. Reusing image candidates across requests cuts latency 37x at K=256 and 191x at K=2048. Code: https://github.com/lllfx/Iris