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Ultra-Low-Bit AI Strikes Back

·2026.04.21 09:58

Key point

With 1.58-bit ternary weights, an 8B model scored 75.5 points.

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Details

PrismML unveiled Ternary Bonsai. It's a language model applying 1.58-bit ternary weights { -1, 0, +1 } across the entire network, released in three sizes: 8B / 4B / 1.7B.

Memory usage is about 9x smaller than regular 16-bit models, with the 8B model running at 1.75GB. They emphasized that embeddings, attention, MLP, and even the LM head all use low-precision representation.

On performance, Ternary Bonsai 8B recorded an average of 75.5 points, 5 points higher than the same-line 1-bit Bonsai 8B (70.5 points). They stated that improvements were consistent across multiple benchmarks including MMLU Redux, MuSR, GSM8K, HumanEval+, IFEval, and BFCLv3.

Speed and power efficiency were also presented.

  • M4 Pro: 82 toks/sec, 0.105 mWh/tok
  • iPhone 17 Pro Max: 27 toks/sec, 0.132 mWh/tok
  • About 5x faster than 16-bit 8B, with 3-4x improved energy efficiency

The model runs natively on Mac / iPhone / iPad via MLX, and the weights are released under an Apache 2.0 license. Detailed training and evaluation methods are provided in a whitepaper.

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