openbmb / BitCPM-CANN-0.5B

GitHub Repo | Technical Report

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Introduction

BitCPM-CANN is the first end-to-end 1.58-bit (ternary) large language model training system natively built on Huawei Ascend NPU. The system integrates quantization-aware training (QAT) into the Megatron-LM framework with MindSpeed acceleration, covering the full training stack from custom ternary operators to distributed parallel training on Ascend 910B.

We train a family of four models—BitCPM-CANN-0.5B/1B/3B/8B—and evaluate them against their full-precision MiniCPM4 counterparts across 11 benchmarks. The 1B/3B/8B models retain 95.7%–97.2% of full-precision performance, while enabling approximately 6× memory reduction at inference time. QAT introduces only 5% training throughput overhead (148 vs. 155 TFLOP/s per NPU).

Key Features

• 🔬 1.58-Bit Ternary Quantization : Compresses model weights to ternary values {-1, 0, 1}, achieving ~90% bit-width reduction compared to BF16.
• 🖥️ Native Ascend NPU Training : First publicly reported 1.58-bit training effort on domestic NPU platform at 8B scale, establishing reusable low-bit training infrastructure for the Ascend ecosystem.
• ⚡ Minimal Training Overhead : Only 5% throughput degradation compared to full-precision training on Ascend 910B.
• 📦 ~6× Inference Memory Reduction : Enables longer contexts, more serving replicas, and edge deployment on consumer devices.

Important Note

The models in this repository are in pseudo-quantized (fake quantization) format . This means the weights are stored in standard floating-point format with ternary values already applied during training. You can load and run inference with these models exactly the same way as full-precision models —no special quantization libraries or custom kernels are required.

BitCPM-CANN Model Family

Usage

Inference with Transformers

Since BitCPM-CANN models are in pseudo-quantized format, you can use them exactly like standard full-precision models:

from transformers import AutoModelForCausalLM, AutoTokenizer
import torch
torch.manual_seed(0)

path = 'openbmb/BitCPM-CANN-0.5B'
device = "cuda"
tokenizer = AutoTokenizer.from_pretrained(path)
model = AutoModelForCausalLM.from_pretrained(path, torch_dtype=torch.bfloat16, device_map=device, trust_remote_code=True)

# User can directly use the chat interface
responds, history = model.chat(tokenizer, "Write an article about Artificial Intelligence.", temperature=0.7, top_p=0.7)
print(responds)

# User can also use the generate interface
# messages = [
#     {"role": "user", "content": "Write an article about Artificial Intelligence."},
# ]
# prompt_text = tokenizer.apply_chat_template(
#     messages,
#     tokenize=False,
#     add_generation_prompt=True,
# )
# model_inputs = tokenizer([prompt_text], return_tensors="pt").to(device)

# model_outputs = model.generate(
#     **model_inputs,
#     max_new_tokens=1024,
#     top_p=0.7,
#     temperature=0.7
# )
# output_token_ids = [
#     model_outputs[i][len(model_inputs[i]):] for i in range(len(model_inputs['input_ids']))
# ]

# responses = tokenizer.batch_decode(output_token_ids, skip_special_tokens=True)[0]
# print(responses)

Evaluation Results

Main Results

BitCPM-CANN models are evaluated against their full-precision MiniCPM4 counterparts across 11 benchmarks spanning commonsense reasoning, domain knowledge, and mathematics & reasoning.

Key Observations

• 1B and above achieve ≥95.7% retention : The 3B model achieves the highest retention at 97.2%, demonstrating that ternary QAT at this scale introduces minimal capability loss.
• 0.5B reveals scale-dependent sensitivity : The smallest model retains 90.1%, indicating that quantization perturbation is more damaging when model capacity is limited.
• 1:1 alignment with MiniCPM4 : The matched evaluation enables direct substitution decisions—deployments can replace specific full-precision models with their ternary counterparts with clearly quantified trade-offs.

Training Efficiency

System-level throughput on 2-node 16-card Ascend 910C:

• 3B model: ~2700 tokens/s per card
• 8B model: ~1340 tokens/s per card

Technical Approach

BitCPM-CANN uses a ternary quantizer that maps each weight group to {-1, 0, 1} scaled by a group-wise factor, trained with Straight-Through Estimator (STE) for gradient flow. The training follows a two-stage strategy: complete QAT followed by post-training distillation , which avoids amplifying training instability during early training.

The system is built as a four-layer vertical stack on Ascend NPU:

1. QAT Training Logic : Ternary quantizer with STE, pluggable quantization layers in Megatron-LM.
2. Megatron-LM Quantized Model Layer : Tensor-parallel linear layers with integrated weight/activation quantizers.
3. Framework Entry Layer : torch_npu and mindspeed.megatron_adaptor injection for NPU execution.
4. Ascend Software-Hardware Stack : MindSpeed, CANN, HCCL communication, Ascend 910B NPU hardware.

For full technical details, please refer to our Technical Report .

Statement

• As a language model, BitCPM-CANN generates content by learning from a vast amount of text.
• However, it does not possess the ability to comprehend or express personal opinions or value judgments.
• Any content generated by BitCPM-CANN does not represent the viewpoints or positions of the model developers.
• Therefore, when using content generated by BitCPM-CANN, users should take full responsibility for evaluating and verifying it on their own.

LICENSE

• This repository and BitCPM-CANN models are released under the Apache-2.0 License.

Citation

• Please cite our technical report if you find our work valuable.

@article{bitcpmcann,
  title={{BitCPM-CANN}: Native 1.58-Bit Large Language Model Training on Ascend NPU},
  author={BitCPM Team},
  year={2026}
}