MTOB
Models learn to translate between English and Kalamang, a language with under 200 speakers, from one grammar book. Scored by chrF.
Cards report half-book or full-book context and either translation direction, so scores vary by setup.
- Made by
- Harvard University and collaborators
- Released
- September 2023
- Kind
- Learning from the context
- Level
- Expert
- Scored
- Checked automatically
- Answers
- Open-ended
- Tasks
- All public
- Strongest model tested
-
Llama 4 Maverick #153 on the capability index
- Last in a launch post
- April 2025, dropped before it saturated
- Last model added
- July 2026
In the authors’ words
Large language models (LLMs) can perform impressive feats with in-context learning or lightweight finetuning. It is natural to wonder how well these models adapt to genuinely new tasks, but how does one find tasks that are unseen in internet-scale training sets? We turn to a field that is explicitly motivated and bottlenecked by a scarcity of web data: low-resource languages. In this paper, we introduce MTOB (Machine Translation from One Book), a benchmark for learning to translate between English and Kalamang – a language with less than 200 speakers and therefore virtually no presence on the web – using several hundred pages of field linguistics reference materials. This task framing is novel in that it asks a model to learn a language from a single human-readable book of grammar explanations, rather than a large mined corpus of in-domain data, more akin to L2 learning than L1 acquisition. We demonstrate that baselines using current LLMs are promising but fall short of human performance, achieving 44.7 chrF on Kalamang to English translation and 45.8 chrF on English to Kalamang translation, compared to 51.6 and 57.0 chrF by a human who learned Kalamang from the same reference materials. We hope that MTOB will help measure LLM capabilities along a new dimension, and that the methods developed to solve it could help expand access to language technology for underserved communities by leveraging qualitatively different kinds of data than traditional machine translation.
Llama 4 Maverick leads with 54.0 among models released by April 2025
Best score per model as labs report them in their own cards. Labs pick their own settings, so these compare less cleanly than independent runs.
The newest model with a score here came out in April 2025, and nobody has reported a newer one. Among the 20 highest-ranked models on the capability index, these have no score yet:
- Claude Fable 5.2
-
Gemini 4 Carbon
- GPT-6 Astra
- Claude Opus 5.5
- and 16 more
- 1
Llama 4 Maverick 54.0
- 2
MiniMax-Text-01 51.7
- 3
Llama 4 Scout 42.2
Source: Labs’ model cards
| # | Model | Score | Setting | Date | Source |
|---|---|---|---|---|---|
| 1 | | 54.0 | Apr 2025 | Lab model card | |
| 2 | | 51.7 | Jan 2025 | Lab model card | |
| 3 | | 42.2 | Apr 2025 | Lab model card |
2 models have held number one in labs’ own numbers since its release in September 2023
Lab claims count from the day the card came out, independent runs from the model’s release.
Source: Labs’ model cards
Scores over time
All the scores we have, one dot each, so a model tested at several settings appears more than once.
Source: Labs’ model cards
No launch post has listed it since April 2025
Launch posts from every lab that has listed it, one tick per post. Tall colored ticks include it, and short gray ones leave it out.
| Date | Launch post | Score | As the post writes it |
|---|---|---|---|
| Apr 5, 2025 | 42.2 | Best of MTOB (half book) eng->kgv/kgv->eng = 42.2/36.6 / MTOB (full book) = 39.7/36.3 | |
| Apr 5, 2025 | 54 | Best of MTOB (half book) eng->kgv/kgv->eng = 54.0/46.4 / MTOB (full book) eng->kgv/kgv->eng = 50.8/46.7 | |
| Jan 15, 2025 | 51.7 | MTOB eng → kalam (ChrF), half book |
5 system cards report it, from 3 labs
Besides launch posts, we read the system cards, model cards and technical reports labs publish with a release. They report far more, including safety and frontier-risk tests.
| Date | Document | Score | As the document writes it | Section |
|---|---|---|---|---|
| Jul 24, 2026 | | MTOB chrF, two directions and two context sizes with no overall score: eng to kgv half book 52.9, full book 54.3; kgv to eng half book 48.6, full book 46.2 (Table 9) | Capabilities | |
| Jul 24, 2026 | | MTOB chrF, two directions and two context sizes with no overall score: eng to kgv half book 50.0, full book 48.9; kgv to eng half book 45.0, full book 42.7 (Table 9) | Capabilities | |
| Apr 5, 2025 | | 42.2 | MTOB (half book) eng->kgv, chrF, instruction tuned. Half book eng->kgv/kgv->eng = 42.2/36.6, full book = 39.7/36.3 (Instruction tuned models table) | Capabilities |
| Apr 5, 2025 | | 54 | MTOB (half book) eng->kgv, chrF, instruction tuned. Half book eng->kgv/kgv->eng = 54.0/46.4, full book = 50.8/46.7 (Instruction tuned models table) | Capabilities |
| Jan 14, 2025 | | 51.7 | MTOB eng → kalam (ChrF), half book (Table 11). Full book 51.60. kalam → eng (BLEURT) half book 57.10 | Capabilities |
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