United States

Recent advances in text-to-SQL have shown that methods such as Group Relative Policy Optimization (GRPO) can substantially improve reasoning performance, but these approaches remain inherently on-policy, limiting their ability to incorporate novel reasoning patterns. In this work, we address this limitation by leveraging existing datasets to generate high-quality off-policy rollouts, enabling mixed-policy training that exposes models to diverse and informative reasoning trajectories. We present the first application of mixed-policy GRPO to the text-to-SQL domain and introduce a systematic study of off-policy data generation strategies for this setting, including a novel method, Iterative Error Correction (IEC), which iteratively refines model outputs through targeted feedback. Our experiments show that mixed-policy GRPO outperforms both base models and on-policy GRPO, yielding average improvements of +4.7% over base models and +4.1% over on-policy GRPO across the Spider and BIRD benchmarks. Gains are particularly strong on BIRD, reaching up to +7.3% over base models and +4.5% over on-policy GRPO.

ACL 2026

Mixed-Policy GRPO for Text-to-SQL with Off-Policy Data Generation

mixed-policy training

grpo

llm reasoning

text-to-sql

reinforcement learning

It is my great pleasure and honor to welcome you to the 64th Annual Meeting of the Association for Computational Linguistics (ACL 2026), held in San Diego, California, USA, July 2–7, 2026. ACL 2026 continues our fields tradition of excellence in scholarship, innovation, and inclusivity, and I am deeply grateful to the many volunteers who have worked tirelessly to bring this event to life.

It is exciting to see the many developments in the field reflected at our conference, such as the advancement of large language models (born out of our community) into many application directions. This is not without challenges, partly due to unsolved problems, and partly due to misuse of the technology. All this is reflected well at ACL 2026. The conference also reflects that the field is not only about advancing technology, but also the science of fundamentally understanding language and how it is use by many different speaker communities. <br>
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workshop paper

Large language models (LLMs) are increasingly evaluated on structured data tasks—table question answering, chart comprehension, graph reasoning, and time series analysis—yet these benchmarks operate in isolation. We ask: does competence in one structured data format predict competence in another when the underlying data and questions are identical? We construct a controlled benchmark of 1,724 programmatically generated questions over 250 sub-tables drawn from 10 datasets spanning 7 domains. Each sub-table is rendered in five formats: Markdown table, chart image, chart text-description, entity-relationship graph, and unlabeled time series. We evaluate six frontier March 2026 LLMs and measure cross-format transfer via tetrachoric correlation on binary (correct/incorrect) outcomes. Our key findings: (1) structured data comprehension skills transfer strongly across text-based formats, with mean tetrachoric r=0.84 between table, graph, and time series representations (r=0.85 overall; r=0.84 for non-ceiling models, confirming the result is not an artifact of high accuracy); (2) chart text-descriptions show consistently lower transfer (r=0.65) despite being length-matched to tables; (3) chart image comprehension is largely siloed, with a 20-50% accuracy gap compared to equivalent text descriptions; and (4) enabling chain-of-thought reasoning improves accuracy by 24-38% for DeepSeek V3.2 but only 0-0.5% for Gemini 3.1 Pro, suggesting reasoning benefits may vary substantially across models. On hard questions (multi-hop and conditional aggregation), transfer remains substantial at r=0.78.

Do Structured Data Comprehension Skills Transfer Across Representation Types? A Systematic Study with Frontier LLMs

Deployed LLM agents rely on textual policies that must evolve from operational experience, yet over long horizons flat-text representations make verification increasingly difficult to sustain as policies grow. We propose Graph-Regularized Agentic Context Evolution (GRACE), which represents policy content as a typed semantic graph and performs scoped structural validation in the local neighborhood of modified nodes, rather than through document-wide consistency analysis. We evaluate GRACE within a fixed operational harness on the telecom domain of $\tau^2$-bench under a controlled distribution-shift protocol. GRACE improves strict reliability (pass^3) from 0.227 to 0.833 and is the only method that sustains improvement over the full trajectory. The three baselines each exhibit a different failure mode, revealing that contradiction avoidance alone is insufficient. Our results suggest that sustained policy evolution may require both a structural substrate for scoped verification and an active mechanism that consolidates accumulated knowledge.

Graph-Regularized Agentic Context Evolution

Large Language Models (LLMs) are increasingly used to generate structured outputs—JSON objects, SQL queries, and structured records—from formal schemas. While recent advances in constrained decoding and schema-aware prompting have improved syntactic compliance, the semantic reliability of these outputs remains poorly characterized. We investigate this gap through the lens of schema drift—the inevitable evolution of database schemas in production environments through column renamings, type changes, and constraint modifications.

We introduce StructHallu-Drift, a benchmark and evaluation framework for studying structured hallucinations under schema evolution. We contribute: (1) a six-category hallucination taxonomy that disentangles syntactic validity from semantic fidelity; (2) a controlled evaluation suite applying realistic schema mutations at three severity levels to established NL-to-structure datasets; and (3) a systematic evaluation of four LLMs spanning 7B to 70B parameters across three structured output tasks.

Experiments on 1,200 schema–model evaluation instances reveal four key findings: (i) 39–54% of structured outputs contain at least one semantic hallucination; (ii) schema drift severity has surprisingly minimal effect on hallucination rates (∼44% across all levels, p = 0.59), suggesting imperfect schema conditioning under our prompting setup; (iii) output format is the dominant factor in generation reliability, with SQL achieving ∼85% semantic validity while schema-grounded record generation drops to 7–24%; (iv) each model exhibits a distinct hallucination fingerprint, implying that mitigation strategies must be model-specific rather than universal. We publicly release our benchmark and evaluation toolkit.

StructHallu-Drift: Benchmarking Structured Hallucinations Under Schema Evolution in LLMs

Recent advances in large language models (LLMs) have significantly enhanced automated legal reasoning. Yet, it remains unclear whether their performance reflects genuine legal reasoning ability or artifacts of data contamination. We present a comprehensive empirical study of tax law reasoning approaches and implement a contamination detection protocol to rigorously assess LLM reliability. We show that performance can be inflated by contamination. Building on this analysis, we conduct a systematic evaluation, comparing monolithic LLMs with hybrid systems that translate statutory text into formal representations and delegate inference to symbolic solvers. We build a novel test suite designed to probe generalization to unseen documents via case and rule variations. Our findings indicate that legal reasoning is inherently compositional and that neuro-symbolic frameworks offer a more reliable and robust foundation for legal AI, as well as improved generalization to unobserved situations.

Reasoners or Translators? Contamination-aware Evaluation and Neuro-Symbolic Robustness on Tax Law

Dense retrievers powered by pretrained embeddings are widely used for document retrieval but struggle in specialized domains due to the mismatches between the training and target domain distributions. Domain adaptation typically requires costly annotation and retraining of query-document pairs. In this work, we revisit an overlooked alternative: applying PCA to domain embeddings to derive lower-dimensional representations that preserve domain-relevant features while discarding non-discriminative components. Though traditionally used for efficiency, we demonstrate that this simple embedding compression can effectively improve retrieval performance. Evaluated across 9 retrievers and 14 MTEB datasets, PCA applied solely to query embeddings improves NDCG@10 in 75.4\% of model-dataset pairs, offering a simple and lightweight method for domain adaptation.

More Than Efficiency: Embedding Compression Improves Domain Adaptation in Dense Retrieval

Recent advances in large language models (LLMs) have greatly improved Text-to-SQL performance for single-table queries. But, it remains challenging in multi-table databases due to complex schema and relational operations. Existing methods often struggle with retrieving the right tables and columns, generating accurate JOINs and UNIONs, and generalizing across diverse schemas. To address these issues, we introduce UNJOIN, a two-stage framework that decouples the retrieval of schema elements from SQL logic generation. 
In the first stage, we merge the column names of all tables in the database into a single-table representation by prefixing each column with its table name. This allows the model to focus purely on accurate retrieval without being distracted by the need to write complex SQL logic. In the second stage, the SQL query is generated on this simplified schema and mapped back to the original schema by reconstructing JOINs, UNIONs, and relational logic. Evaluations on SPIDER and BIRD datasets show that UNJOIN matches or exceeds the state-of-the-art baselines. UNJOIN uses only schema information, which does not require data access or fine-tuning, making it scalable and adaptable across databases. Our code is available at: https://github.com/coral-lab-asu/unjoin

UNJOIN: Enhancing Multi-Table Text-to-SQL Generation via Schema Simplification

Large Language Models (LLMs) often underperform in domain adaptation for industrial settings, where available corpora are limited and structurally diverse. These corpora frequently include non-natural formats such as tables, entity lists, or bullet-point instructions that hinder effective learning. To understand and improve domain adaptive pretraining on such data, we introduce SParK-Eval (Structure-aware Parametric Knowledge Evaluation), a framework that constructs question–answer pairs from pretraining data and annotates each with its input structure (e.g., natural sentence, table, list). This enables fine-grained analysis of how input structure affects parametric knowledge acquisition during DAPT. Additionally, we propose a prompt-based input normalization method that converts diverse inputs into coherent natural sentences, providing a reference for isolating structural effects. Our experiments show that LLMs acquire substantially more knowledge from natural sentences than from their structurally non-standard counterparts. These findings underscore the importance of structure-aware evaluation in diagnosing learning challenges and guiding effective domain adaptation strategies.

SParK-Eval: Evaluating Structure-Aware Knowledge Acquisition in LLMs for Domain Adaptation to Industrial Records

We introduce SciTaRC, an expert-authored benchmark for question answering over scientific tables that targets composite, multi-step reasoning. To enable fine-grained diagnostic analysis beyond end-task accuracy, SciTaRC pairs each question with a manually constructed reasoning plan and explicit complexity metrics. State-of-the-art models fail on at least 23\% of these questions, while highly capable open-weight models like Llama-3.3-70B collapse on 65.5\% of the benchmark. Error analysis shows that, in zero-shot settings, failures are driven primarily by question comprehension, where models misinterpret the scientific query and derive the wrong reasoning objective. To determine whether overcoming this gap is sufficient, we use structured plans to decouple strategy formulation from execution. Surprisingly, providing step-by-step oracle plans yields only limited gains and fails to eliminate the performance gap. This reveals a substantial execution bottleneck: both natural language and code-based methods struggle to reliably carry out long-horizon computational chains over structured data. Ultimately, SciTaRC serves as a rigorous diagnostic testbed for studying both planning and execution in scientific table reasoning.

SciTaRC: Benchmarking QA on Scientific Tabular Data that Requires Language Reasoning and Complex Computation

Despite its real-world significance, model performance on tabular data remains underexplored, leaving uncertainty about which model to rely on and which prompt configuration to adopt. To address this gap, we create ToRR, a benchmark for Table Reasoning and Robustness, measuring model performance and robustness on table-related tasks. The benchmark includes 10 datasets that cover different types of table reasoning capabilities across varied domains. ToRR goes beyond model performance rankings, and is designed to reflect whether models can handle tabular data consistently and robustly, across a variety of common table representation formats. We present a leaderboard as well as comprehensive analyses of the results of leading models over ToRR. Our results reveal a striking pattern of brittle model behavior, where even strong models are unable to perform robustly on tabular data tasks. We further find that no single table format consistently yields superior performance. However, evaluating models across multiple formats is essential for a reliable assessment of their capabilities. Moreover, we show that the reliability boost from testing multiple prompts can be equivalent to adding more test examples. Overall, our findings show that reasoning over table tasks remains a significant challenge. The leaderboard, data and code are publicly available.

The Mighty ToRR: A Benchmark for Table Reasoning and Robustness in LLMs

Knowledge Graph-to-Text (G2T) generation involves verbalizing structured knowledge graphs into natural language text. Recent advancements in Pretrained Language Models (PLMs) have improved G2T performance, but their effectiveness relies on datasets with precise graph-text alignment. However, the scarcity of high-quality, general-domain G2T generation datasets restricts progress in the general-domain G2T generation research. To address this issue, we introduce Wikipedia Ontology-Free Graph-text dataset (WikiOFGraph), a new large-scale G2T dataset generated using a novel method that leverages Large Language Models (LLMs) and Data-QuestEval. Our dataset, which contains 5.85M general-domain graph-text pairs, offers high graph-text consistency without reliance on external ontologies. Experimental results demonstrate that PLM fine-tuned on WikiOFGraph outperforms those trained on other datasets across various evaluation metrics. Our method proves to be a scalable and effective solution for generating high-quality G2T data, significantly advancing the field of G2T generation.

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