---
license: apache-2.0
library_name: transformers
pipeline_tag: text-generation
tags:
- speculative-decoding
- pipeline-parallelism
- llm-acceleration
---

# Speculative Pipeline Decoding: Speculation Head Checkpoints

This repository contains pre-trained **pipeline speculation head** weights for the paper [Speculative Pipeline Decoding: Higher-Accruacy and Zero-Bubble Speculation via Pipeline Parallelism](https://huggingface.co/papers/2605.30852).

Speculative Pipeline Decoding (SPD) is a framework that unlocks the potential of pipeline parallelism for LLM decoding acceleration. By partitioning the target LLM into $n$ pipeline stages, SPD allows the model to process $n$ tokens in parallel, achieving higher acceptance rates and zero latency bubbles.

- **Paper:** [https://huggingface.co/papers/2605.30852](https://huggingface.co/papers/2605.30852)
- **Code:** [https://github.com/yuyijiong/speculative_pipeline_decoding](https://github.com/yuyijiong/speculative_pipeline_decoding)

## Quick Start (Inference)

To run inference using these checkpoints, clone the official repository and use the provided `pipeline_inference.py` script. You must pair the speculation head with the corresponding base model it was trained on.

```bash
python pipeline_inference.py \
  --spec_head_ckpt /path/to/checkpoint.pt \
  --base_model_path Qwen/Qwen3.5-4B \
  --max_new_tokens 100 \
  --temperature 0.0
```

## Checkpoint Information

Each `.pt` file is a single checkpoint produced by training. For more details on training and evaluation, see the [official repo](https://github.com/yuyijiong/speculative_pipeline_decoding).

### Filename format

Files are named:
`{model}_s{num_stages}_l{num_spec_layers}.pt`

| Part | Meaning |
|------|---------|
| `{model}` | Base model tag (e.g. `Qwen3.5-4B`, `Qwen3.5-9B`) |
| `s{...}` | `num_stages` — pipeline depth (number of target-model stages) |
| `l{...}` | `num_spec_layers` — number of Transformer layers in the speculation module |

Example: `Qwen3.5-9B_s16_l2.pt` → Qwen3.5-9B base, 16 stages, 2 spec layers.

### Checkpoint contents

Each file is a PyTorch archive with two top-level keys:

```python
{
    "state_dict": ...,  # weights of the speculation module
    "config": { ... },  # hyperparameters and metadata
}
```

### `config` fields (always present)

| Field | Description |
|-------|-------------|
| `base_model_path` | Base model path recorded at training time (can be overridden via `--base_model_path` at load time) |
| `hidden_size` | Hidden size (matches base model) |
| `vocab_size` | Base model vocabulary size |
| `draft_vocab_size` | Draft head output size (full vocab or draft subset) |
| `num_stages` | Pipeline depth (same as `s` in filename) |
| `num_spec_layers` | Speculation module depth (same as `l` in filename) |
| `version` | Checkpoint format version (`10`) |
| `trained_with_use_deepest` | Whether training used deepest-layer features |
| `shallow_hidden_layer_indices` | Which base layers feed the speculation module |

## Citation

If you use this work, please cite our paper:

```bibtex
@misc{yu2026speculativepipelinedecodinghigheraccruacy,
      title={Speculative Pipeline Decoding: Higher-Accruacy and Zero-Bubble Speculation via Pipeline Parallelism}, 
      author={Yijiong Yu and Huazheng Wang and Shuai Yuan and Ruilong Ren and Ji Pei},
      year={2026},
      eprint={2605.30852},
      archivePrefix={arXiv},
      primaryClass={cs.CL},
      url={https://arxiv.org/abs/2605.30852}, 
}
```