| --- |
| license: cc-by-nc-nd-4.0 |
| pretty_name: "HAT: Hallucination Annotation for Translation" |
| size_categories: |
| - 100K<n<1M |
| annotations_creators: |
| - expert-generated |
| task_categories: |
| - translation |
| - text-classification |
| language: |
| - ar |
| - nl |
| - en |
| - fr |
| - de |
| - hi |
| - id |
| - it |
| - ja |
| - ko |
| - pl |
| - pt |
| - ru |
| - zh |
| - es |
| - th |
| - tr |
| - uk |
| - vi |
| tags: |
| - machine-translation |
| - hallucination-detection |
| - mt-evaluation |
| configs: |
| - config_name: default |
| data_files: |
| - {split: train, path: "data/train/*/*.parquet"} |
| - {split: validation, path: "data/dev/*/*.parquet"} |
| - {split: test, path: "data/test/*/*.parquet"} |
| - config_name: ar_AE-en_US |
| data_files: |
| - {split: train, path: "data/train/ar_AE-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/ar_AE-en_US/*.parquet"} |
| - {split: test, path: "data/test/ar_AE-en_US/*.parquet"} |
| - config_name: de_DE-en_US |
| data_files: |
| - {split: train, path: "data/train/de_DE-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/de_DE-en_US/*.parquet"} |
| - {split: test, path: "data/test/de_DE-en_US/*.parquet"} |
| - config_name: en_US-ar_AE |
| data_files: |
| - {split: train, path: "data/train/en_US-ar_AE/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-ar_AE/*.parquet"} |
| - {split: test, path: "data/test/en_US-ar_AE/*.parquet"} |
| - config_name: en_US-de_DE |
| data_files: |
| - {split: train, path: "data/train/en_US-de_DE/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-de_DE/*.parquet"} |
| - {split: test, path: "data/test/en_US-de_DE/*.parquet"} |
| - config_name: en_US-es_ES |
| data_files: |
| - {split: train, path: "data/train/en_US-es_ES/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-es_ES/*.parquet"} |
| - {split: test, path: "data/test/en_US-es_ES/*.parquet"} |
| - config_name: en_US-fr_FR |
| data_files: |
| - {split: train, path: "data/train/en_US-fr_FR/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-fr_FR/*.parquet"} |
| - {split: test, path: "data/test/en_US-fr_FR/*.parquet"} |
| - config_name: en_US-hi_IN |
| data_files: |
| - {split: train, path: "data/train/en_US-hi_IN/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-hi_IN/*.parquet"} |
| - {split: test, path: "data/test/en_US-hi_IN/*.parquet"} |
| - config_name: en_US-id_ID |
| data_files: |
| - {split: train, path: "data/train/en_US-id_ID/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-id_ID/*.parquet"} |
| - {split: test, path: "data/test/en_US-id_ID/*.parquet"} |
| - config_name: en_US-it_IT |
| data_files: |
| - {split: train, path: "data/train/en_US-it_IT/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-it_IT/*.parquet"} |
| - {split: test, path: "data/test/en_US-it_IT/*.parquet"} |
| - config_name: en_US-ja_JP |
| data_files: |
| - {split: train, path: "data/train/en_US-ja_JP/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-ja_JP/*.parquet"} |
| - {split: test, path: "data/test/en_US-ja_JP/*.parquet"} |
| - config_name: en_US-ko_KR |
| data_files: |
| - {split: train, path: "data/train/en_US-ko_KR/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-ko_KR/*.parquet"} |
| - {split: test, path: "data/test/en_US-ko_KR/*.parquet"} |
| - config_name: en_US-nl_NL |
| data_files: |
| - {split: train, path: "data/train/en_US-nl_NL/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-nl_NL/*.parquet"} |
| - {split: test, path: "data/test/en_US-nl_NL/*.parquet"} |
| - config_name: en_US-pl_PL |
| data_files: |
| - {split: train, path: "data/train/en_US-pl_PL/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-pl_PL/*.parquet"} |
| - {split: test, path: "data/test/en_US-pl_PL/*.parquet"} |
| - config_name: en_US-pt_BR |
| data_files: |
| - {split: train, path: "data/train/en_US-pt_BR/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-pt_BR/*.parquet"} |
| - {split: test, path: "data/test/en_US-pt_BR/*.parquet"} |
| - config_name: en_US-ru_RU |
| data_files: |
| - {split: train, path: "data/train/en_US-ru_RU/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-ru_RU/*.parquet"} |
| - {split: test, path: "data/test/en_US-ru_RU/*.parquet"} |
| - config_name: en_US-th_TH |
| data_files: |
| - {split: train, path: "data/train/en_US-th_TH/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-th_TH/*.parquet"} |
| - {split: test, path: "data/test/en_US-th_TH/*.parquet"} |
| - config_name: en_US-tr_TR |
| data_files: |
| - {split: train, path: "data/train/en_US-tr_TR/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-tr_TR/*.parquet"} |
| - {split: test, path: "data/test/en_US-tr_TR/*.parquet"} |
| - config_name: en_US-uk_UA |
| data_files: |
| - {split: train, path: "data/train/en_US-uk_UA/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-uk_UA/*.parquet"} |
| - {split: test, path: "data/test/en_US-uk_UA/*.parquet"} |
| - config_name: en_US-vi_VN |
| data_files: |
| - {split: train, path: "data/train/en_US-vi_VN/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-vi_VN/*.parquet"} |
| - {split: test, path: "data/test/en_US-vi_VN/*.parquet"} |
| - config_name: en_US-zh_CN |
| data_files: |
| - {split: train, path: "data/train/en_US-zh_CN/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-zh_CN/*.parquet"} |
| - {split: test, path: "data/test/en_US-zh_CN/*.parquet"} |
| - config_name: en_US-zh_TW |
| data_files: |
| - {split: train, path: "data/train/en_US-zh_TW/*.parquet"} |
| - {split: validation, path: "data/dev/en_US-zh_TW/*.parquet"} |
| - {split: test, path: "data/test/en_US-zh_TW/*.parquet"} |
| - config_name: es_ES-en_US |
| data_files: |
| - {split: train, path: "data/train/es_ES-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/es_ES-en_US/*.parquet"} |
| - {split: test, path: "data/test/es_ES-en_US/*.parquet"} |
| - config_name: fr_FR-en_US |
| data_files: |
| - {split: train, path: "data/train/fr_FR-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/fr_FR-en_US/*.parquet"} |
| - {split: test, path: "data/test/fr_FR-en_US/*.parquet"} |
| - config_name: hi_IN-en_US |
| data_files: |
| - {split: train, path: "data/train/hi_IN-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/hi_IN-en_US/*.parquet"} |
| - {split: test, path: "data/test/hi_IN-en_US/*.parquet"} |
| - config_name: id_ID-en_US |
| data_files: |
| - {split: train, path: "data/train/id_ID-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/id_ID-en_US/*.parquet"} |
| - {split: test, path: "data/test/id_ID-en_US/*.parquet"} |
| - config_name: it_IT-en_US |
| data_files: |
| - {split: train, path: "data/train/it_IT-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/it_IT-en_US/*.parquet"} |
| - {split: test, path: "data/test/it_IT-en_US/*.parquet"} |
| - config_name: ja_JP-en_US |
| data_files: |
| - {split: train, path: "data/train/ja_JP-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/ja_JP-en_US/*.parquet"} |
| - {split: test, path: "data/test/ja_JP-en_US/*.parquet"} |
| - config_name: ko_KR-en_US |
| data_files: |
| - {split: train, path: "data/train/ko_KR-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/ko_KR-en_US/*.parquet"} |
| - {split: test, path: "data/test/ko_KR-en_US/*.parquet"} |
| - config_name: nl_NL-en_US |
| data_files: |
| - {split: train, path: "data/train/nl_NL-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/nl_NL-en_US/*.parquet"} |
| - {split: test, path: "data/test/nl_NL-en_US/*.parquet"} |
| - config_name: pl_PL-en_US |
| data_files: |
| - {split: train, path: "data/train/pl_PL-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/pl_PL-en_US/*.parquet"} |
| - {split: test, path: "data/test/pl_PL-en_US/*.parquet"} |
| - config_name: pt_BR-en_US |
| data_files: |
| - {split: train, path: "data/train/pt_BR-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/pt_BR-en_US/*.parquet"} |
| - {split: test, path: "data/test/pt_BR-en_US/*.parquet"} |
| - config_name: ru_RU-en_US |
| data_files: |
| - {split: train, path: "data/train/ru_RU-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/ru_RU-en_US/*.parquet"} |
| - {split: test, path: "data/test/ru_RU-en_US/*.parquet"} |
| - config_name: th_TH-en_US |
| data_files: |
| - {split: train, path: "data/train/th_TH-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/th_TH-en_US/*.parquet"} |
| - {split: test, path: "data/test/th_TH-en_US/*.parquet"} |
| - config_name: tr_TR-en_US |
| data_files: |
| - {split: train, path: "data/train/tr_TR-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/tr_TR-en_US/*.parquet"} |
| - {split: test, path: "data/test/tr_TR-en_US/*.parquet"} |
| - config_name: uk_UA-en_US |
| data_files: |
| - {split: train, path: "data/train/uk_UA-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/uk_UA-en_US/*.parquet"} |
| - {split: test, path: "data/test/uk_UA-en_US/*.parquet"} |
| - config_name: vi_VN-en_US |
| data_files: |
| - {split: train, path: "data/train/vi_VN-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/vi_VN-en_US/*.parquet"} |
| - {split: test, path: "data/test/vi_VN-en_US/*.parquet"} |
| - config_name: zh_CN-en_US |
| data_files: |
| - {split: train, path: "data/train/zh_CN-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/zh_CN-en_US/*.parquet"} |
| - {split: test, path: "data/test/zh_CN-en_US/*.parquet"} |
| - config_name: zh_TW-en_US |
| data_files: |
| - {split: train, path: "data/train/zh_TW-en_US/*.parquet"} |
| - {split: validation, path: "data/dev/zh_TW-en_US/*.parquet"} |
| - {split: test, path: "data/test/zh_TW-en_US/*.parquet"} |
| --- |
| |
| # HAT: Hallucination Annotation for Translation |
|
|
|
|
| ## 🧭 Table of Contents |
| - [Overview](#-overview) |
| - [Usage](#-usage) |
| - [Data Creation Process](#-data-creation-process) |
| - [Data Statistics](#-data-statistics) |
| - [Dataset Structure](#-dataset-structure) |
| - [Paper Abstract](#-paper-abstract) |
| - [Citation](#-citation) |
| - [License](#-license) |
|
|
| --- |
|
|
| ## 📘 Overview |
| **HAT (Hallucination Annotation for Translation)** is a large-scale dataset for **hallucination detection in machine translation (MT)**. |
| It is released as part of our publication at ACL 2026 ([paper](https://aclanthology.org/2026.acl-long.721.pdf)). |
|
|
| - **350,959 span-level annotated samples** |
| - **38 language pairs** |
| - **~8,000-10,000 samples per language pair**, divided into **train**, **dev**, and **test** sets |
| - **Annotations** by professional translators under strict **quality control** |
|
|
| HAT enables research on detecting and mitigating hallucinations in MT systems. |
|
|
| --- |
|
|
| ## 🚀 Usage |
| Load the dataset with the 🤗 [`datasets`](https://huggingface.co/docs/datasets) library: |
|
|
| ```python |
| from datasets import load_dataset |
| |
| # All 38 language pairs |
| ds = load_dataset("apple/hat") |
| train, validation, test = ds["train"], ds["validation"], ds["test"] |
| |
| # A single language pair (e.g. English → Japanese) |
| ds = load_dataset("apple/hat", "en_US-ja_JP") |
| ``` |
|
|
| The available config names are the 38 language pairs (e.g. `en_US-ja_JP`, `fr_FR-en_US`); the |
| default config concatenates all pairs. Each config exposes `train`, `validation`, and `test` splits. |
|
|
| --- |
|
|
| ## ⚙️ Data Creation Process |
| The dataset was created through the following steps: |
|
|
| 1. **Data Collection:** |
| Crawled ~5M sentences per language from the web, filtered by language ID, length, and deduplication. |
|
|
| 2. **Translation:** |
| Translated monolingual sentences into target languages using a strong neural MT model. |
|
|
| 3. **Sample Selection:** |
| Selected translations with lower quality (based on quality metrics) to increase the likelihood of hallucinations. |
|
|
| 4. **Annotation:** |
| Professional translators labeled hallucinations under rigorous quality control. |
|
|
| 5. **Post-processing:** |
| Removed samples with issues in source text to ensure data integrity. |
|
|
| --- |
|
|
| ## 📊 Data Statistics |
|
|
| | Split | Samples per language pair | |
| |--------|----------------------------| |
| | **Train** | ~10,000 | |
| | **Dev** | ~2,000 | |
| | **Test** | ~3,000 | |
|
|
| --- |
|
|
| ## 📂 Dataset Structure |
| Datasets are organized in the [`data/`](data/) directory: |
| ``` |
| data/ |
| ├── train/ |
| ├── dev/ |
| └── test/ |
| ``` |
| Each split contains subdirectories for each language pair which contains one parquet file. |
|
|
| > **Split naming:** the parquet files live under `data/train`, `data/dev`, and `data/test`. |
| > On the Hugging Face Hub the `dev` files are exposed as the standard `validation` split, so |
| > `load_dataset(...)` returns `train` / `validation` / `test`. |
| |
| **Schema:** |
| |
| | Field | Type | Description | |
| |--------|------|-------------| |
| | `source_locale` | `string` | Locale of the source text | |
| | `source_text` | `string` | Source sentence | |
| | `target_locale` | `string` | Locale of the target text | |
| | `target_text` | `string` | Machine-translated output | |
| | `split` | `string` | Dataset split (`train` / `dev` / `test`) | |
| | `label` | `int64` | Binary hallucination label (`0`: no hallucination, `1`: contains hallucination) | |
| | `score` | `float64` | Proportion (0–1) of hallucinated characters | |
| | `annotation` | `string` | Raw span-level hallucination annotation | |
|
|
|
|
| ## 📄 Paper Abstract |
| Hallucinations in machine translation (MT)—outputs that may be fluent yet unfaithful to the source content—remain a critical obstacle. They hinder the reliable deployment of MT systems in real-world applications. Despite growing attention to this phenomenon, progress has been constrained by the lack of large-scale, high-quality benchmarks dedicated to hallucination detection. We introduce HAT (Hallucination Annotation for Translation), a novel dataset designed to advance research on this problem. HAT comprises 350,959 span-level annotated samples across 38 language pairs, with approximately 8,000–10,000 samples per pair partitioned into training, development, and test sets. Annotations were produced by professional translators under rigorous quality control protocols to ensure reliability. We provide a detailed analysis of hallucination distributions and establish benchmark performance using a diverse set of baselines, including automatic MT evaluation metrics as well as large language models. By providing the first large-scale, systematically annotated resource for hallucination detection in MT, HAT enables the development of more faithful translation models and lays the groundwork for future research on building trustworthy machine translation systems. |
|
|
| ## 📚 Citation |
| If you use this dataset, please cite: |
|
|
| ```bibtex |
| @inproceedings{chatterjee-etal-2026-hat, |
| title = "{HAT}: Hallucination Annotation for Translation", |
| author = "Chatterjee, Rajen and |
| Li, Xintong and |
| Charoenpornsawat, Paisarn and |
| Lee, Allen", |
| editor = "Liakata, Maria and |
| Moreira, Viviane P. and |
| Zhang, Jiajun and |
| Jurgens, David", |
| booktitle = "Proceedings of the 64th Annual Meeting of the {A}ssociation for {C}omputational {L}inguistics (Volume 1: Long Papers)", |
| month = jul, |
| year = "2026", |
| address = "San Diego, California, United States", |
| publisher = "Association for Computational Linguistics", |
| url = "https://aclanthology.org/2026.acl-long.721/", |
| pages = "15865--15888", |
| ISBN = "979-8-89176-390-6", |
| } |
| ``` |
|
|
| ## 📄 License |
| The HAT dataset is licensed under CC BY-NC-ND 4.0 (https://creativecommons.org/licenses/by-nc-nd/4.0/). |
