Crane Nemotron 4B

An experimental hybrid-architecture model for East African languages and agentic tool-calling.

Crane Nemotron 4B is a research model from Crane AI Labs exploring hybrid Mamba + Transformer architectures for multilingual and agentic use. Most open language models are pure Transformers. This one is not: it is built on NVIDIA's Nemotron-Nano (NemotronH) backbone, which interleaves Mamba-2 state-space layers with attention layers. We were curious how well a hybrid SSM/attention model absorbs low-resource languages and structured tool use, so we adapted it to seven East African languages, taught it agentic tool-calling, and used reinforcement learning to correct multilingual drift and tool-triggering.

This is an experiment, shared in that spirit. The numbers and behavior below are what we measured, including where the model still falls short.

Highlights

  • Hybrid architecture (Mamba-2 state-space + attention), not a pure Transformer.
  • 7 East African languages: Amharic, English, Hausa, Kinyarwanda, Luganda, Somali, Swahili.
  • Agentic tool-calling: web search, weather, and calculator, with a 90% tool-trigger decision accuracy.
  • Large reasoning and knowledge gains over the base checkpoint after continued pretraining, unified SFT, and RL.

Strengths (measured)

Benchmark Base Crane Nemotron 4B
MMLU (knowledge) 29.8 53.8
GSM8K (math reasoning) 60.4 75.2
Tool-trigger accuracy (80 cases) ~52 (SFT) 90
Language-consistency reward (RL) 0.73 0.90
FLORES X to English chrF Swahili 49 / Luganda 36
  • Coherent multilingual chat and persona across the seven languages.
  • Tool over-calling eliminated; tool under-calling reduced to 6/40 on the balanced eval.
  • Translation into English is strong for the higher-resource languages (Swahili, Luganda).

Limitations

We prefer to be direct about what does not work yet.

  • AfriMMLU is near chance (~23%): multilingual knowledge QA remains weak.
  • English-to-X generation is weaker than X-to-English.
  • Amharic generation (Ge'ez script) is currently unreliable.
  • Calculator tool still occasionally narrates ("let me use the calculator...") instead of emitting the call on harder expressions (residual ~6/40 under-call).
  • This is a research checkpoint, not a production-hardened model.

Architecture and training

  • Base: NVIDIA Nemotron-Nano 4B (NemotronH), a hybrid Mamba-2 + Transformer model.
  • Pipeline: continued pretraining on East African language data, unified capability SFT (chat + persona + tool-calling in one pass so nothing washes out), then GRPO reinforcement learning for language consistency and tool-triggering.
  • Tool-calling uses the qwen3_xml tool-call format and supports OpenAI-style tools with tool_choice="auto".

Intended use

Research and experimentation with hybrid architectures for African-language and agentic applications. Not intended for high-stakes or unsupervised production use.

Acknowledgements

Built on NVIDIA Nemotron-Nano. Developed by Crane AI Labs as part of ongoing work on East African language models and hybrid architectures.

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