arXiv Machine Learning

PixSim: a calibrated open-source simulator of instant-payment fraud, recovery and interdiction under analyst capacity constraints

PixSim is an open‑source simulator that models Brazil’s Pix instant‑payment system, incorporating irreversible settlement, a regulated recovery mechanism (MED), downstream fund dispersal, and capacity‑constrained analyst review. Calibrated to Banco Central do Brasil data, the model reproduces the 2025 recovery rate within 0.006 and its decomposition within 0.02, and projects future performance under various policy scenarios. Benchmark tests show how staffing levels, alert expiry rules, and scorer quality affect recovery outcomes and false‑block harm.

arXiv AI
2d ago

The Harness Is the Model: Agent Scaffolding Changes a Fixed LLM's Compliance with Banking Conduct Rules, Unevenly Across Models

The study examines how different harness configurations affect a fixed large language model’s compliance with banking conduct rules. Four open‑weight models were tested across five harnesses on 156 pre‑registered retail‑banking scenarios, yielding 3,120 two‑turn episodes scored for rule violations and over‑refusals. Results show that while overall compliance rates varied modestly (87.3%–92.1%), the impact of a harness differed markedly between models, with some models’ best and worst harnesses differing by over 10 percentage points and a same‑model compliance reviewer reducing violations from 9.6% to 6.4%. whyItMatters":"The findings suggest that validating a model’s compliance requires testing the specific model‑harness pair rather than the model alone, highlighting the importance of action logs over conversation transcripts for accurate conduct assessment."

By Mehmet Murat Huyut
arXiv AI
Aug 19

An Omitted Mode Is a Rare Rule: The Sampling-Verification Danger Law in Continuous Code World Models

The paper investigates the safety of Code World Models, where a language model generates executable world models that a planner uses. It shows that accepting a model based on sampled transitions only guarantees sample consistency, not full safety, because the probability of missing critical events decays as (1‑r)^N. Experiments on hybrid instruments reveal that omitted mode‑boundaries can severely limit planner performance, and that even sophisticated LLMs (GPT‑5.x) struggle to repair such omissions in higher‑dimensional settings.

By Javier Aguilar Mart\'in
arXiv AI
Oct 27

FraudSociety: A Generative Agent-Based Society for the Financial-Fraud Economy

FraudSociety is a novel LLM‑agent‑based simulator that jointly models informational and financial dynamics in the financial‑fraud economy. It features a dynamic social environment, persistent financial ledgers, and a Need‑Intent‑Action architecture, allowing fraudsters to adapt their actions based on interaction histories and ledger states. Validation shows macro‑level outcomes match real‑world patterns, micro‑level loss concentration aligns with Canadian statistics, and personalized interventions can dramatically reduce repeat‑payment rates.

By Keyang Chen, Mingxuan Jiang, Zeping Li, Yiwen Zhao, Yifan Wang, Qiuyang Zhang, Shuaicheng Qi, Yicun Liu, Zhixin Li, Sen Liu, Yinan Jing, Guangnan Ye, Hongfeng Chai
arXiv AI
Sep 7

FinalityBench: An Effect-Level Benchmark for Agent Decisions Under Delayed and Conflicting Financial Finality

FinalityBench is an executable benchmark that tests how agents decide on shipping, re‑capturing, refunding, or waiting when a merchant’s payment processor, ledger, ERP, and bank feed receive delayed, duplicated, dropped, or reordered messages, causing contradictory beliefs about an order. The benchmark uses a hidden canonical event log and faulted delivery streams to generate system views, scoring each episode by the merchant’s terminal economic position relative to a privileged reference. It contains 321 tasks, including 45 twin pairs where all four views are identical yet the correct disposition differs, and evaluates nine programmatic policies, revealing that a ship‑on‑first‑sign policy performs best by accuracy but worst by paired loss, while a runtime‑gated irreversible‑action policy achieves 85.4% accuracy without losing money.

By Abhishek Sharma
Hugging Face Trending Papers
Aug 18

An Omitted Mode Is a Rare Rule: The Sampling-Verification Danger Law in Continuous Code World Models

The paper investigates the safety of Code World Models, where a language model generates an executable world model that a planner uses, and the model is accepted if it reproduces sampled transitions. It defines the pipeline’s danger as the expected risk, showing that the probability of missing a critical event across N independent rollouts is (1‑r)^N, and that an additional acceptance sample adds to the exponent. Experiments on hybrid instruments reveal that mode‑blind models can be exploited, and the authors provide theoretical bounds on localization budgets and demonstrate that acceptance only guarantees sample consistency, covering about two percent of the planner’s queries.

arXiv AI
Sep 18

Refuse, Decompose, Refresh: A Claim-Safe Protocol for Closed-Loop AI Evaluation

The paper introduces a claim‑safe protocol for evaluating closed‑loop AI systems, consisting of three actions: Refuse, Decompose, and Refresh. It demonstrates the protocol in a simulator with 24 policy components and 1,440 held‑out cases, showing that abstention and stable false admission rates are low while providing detailed statistical diagnostics. The approach emphasizes that evaluation results should be tied to observable support and statistical calibration rather than a single PASS/FAIL label.

By Peiying Zhu, Sidi Chang
arXiv AI
Sep 25

Where Does Exactly-Once Live? Model, Harness, and Tool-Contract Effects on Duplicate Side Effects in LLM Agents

The paper investigates where exactly‑once semantics should be enforced for tool‑using agents—within the model, the agent harness, or the tool contract—by evaluating 25,930 episodes across nine models, three harnesses, two contract variants, and fifteen recovery conditions. Using the LIMBO sandbox, the study shows that when an immediate read‑back is available, frontier models rarely duplicate lost acknowledgements, whereas weaker models do; when read‑back is unavailable, the contract’s idempotency keys explain most duplicate behavior. The authors prove that verification‑only policies cannot guarantee exactly‑once under late commits without bounded in‑flight time, and that waiting only helps when delays are short and predictable. whyItMatters":"The findings clarify that enforcing exactly‑once semantics largely depends on the tool contract and fault type, guiding designers on where to focus reliability mechanisms for LLM agents."

By Jiapeng Li