# Speculative Decoding

[![Documentation](https://img.shields.io/badge/Docs-NVIDIA--Model--Optimizer-blue?logo=readthedocs&style=flat-square)](https://nvidia.github.io/Model-Optimizer/guides/5_speculative_decoding.html)

Speculative decoding accelerates auto-regressive generation in large language models (LLMs) by leveraging a lightweight draft model to predict the next γ tokens. The main LLM then verifies these candidate tokens in a single forward pass. If the draft model correctly predicts α tokens, the LLM can accept and generate α+1 tokens per verification step, significantly improving generation speed.

This folder contains an end-to-end runnable speculative decoding fine‑tuning pipeline in which Llama‑3.2‑1B (Hugging Face) is trained on the [Daring-Anteater](https://huggingface.co/datasets/nvidia/Daring-Anteater) dataset.

This example focuses on training with Hugging Face. To train with Megatron‑LM, see the [Megatron‑LM example](https://github.com/NVIDIA/Megatron-LM/tree/main/examples/post_training/modelopt).

## Contents

<div align="center">

| **Section** | **Description** | **Jump To** |
| :------------: | :------------: | :------------: |
| Pre-Requisites | Required & optional dependencies | \[[Link](#pre-requisites)\] |
| Simplified Workflow | Train, evaluate, and export EAGLE model with one-line command | \[[Link](#getting-started-simplified-workflow)\] |
| Online Training | Train draft model alongside base model in GPU memory | \[[Link](#training-draft-model-with-online-base-model)\] |
| Offline Training | Train draft model using pre-computed hidden states | \[[Link](#training-draft-model-with-offline-base-model)\] |
| Streaming Training | Train draft on hidden states streamed from a live vLLM serve (no disk dump) | \[[Link](#training-draft-model-with-streaming-base-model)\] |
| After Training | Evaluation, export and deployment | \[[Link](#model-validation)\] |
| Advanced Usage | Data synthesis, vocab compression, and configuration | \[[Link](#advanced-usage)\] |
| Support Matrix | Supported models for speculative decoding training | \[[Link](#support-matrix)\] |
| Speculation Module Checkpoints | View pre-trained speculation modules ready to deploy! | \[[Link](#speculation-module-checkpoints)\] |
| Resources | Extra links to relevant resources | \[[Link](#resources)\] |

</div>

## Pre-Requisites

### Docker

Please use the PyTorch docker image (e.g., `nvcr.io/nvidia/pytorch:25.08-py3`) or visit our [installation docs](https://nvidia.github.io/Model-Optimizer/getting_started/2_installation.html) for more information.

Also follow the installation steps below to upgrade to the latest version of Model Optimizer and install dataset and example-specific dependencies.

### Local Installation

Install Modelopt with `hf` dependencies and other requirements for this example:

```bash
pip install -U nvidia-modelopt[hf]
pip install -r requirements.txt
```

### Data Preparation

We support a range of input datasets. In this example, we will use the [Daring-Anteater](https://huggingface.co/datasets/nvidia/Daring-Anteater) dataset.

```bash
python ../dataset/make_dataset.py -f ../dataset/example_data_config.yaml --full-conversations
```

See [other-datasets](#other-datasets) section for other dataset options and instruction for user-provided data.

Omit `--full-conversations` if you plan to run synthetic data generation (see [data-synthesis](#data-synthesis)).

For large-scale training with NVIDIA's Nemotron datasets, use the dedicated scripts described in [Nemotron Datasets](#nemotron-datasets).

## Getting Started: Simplified Workflow

```bash
bash train_eagle3_and_export.sh --base_model meta-llama/Llama-3.2-1B-Instruct
```

This one-line command runs a minimal example workflow of training and exporting an EAGLE draft model in Modelopt. Specifically, it

- Initializes the draft model with [default settings](https://github.com/NVIDIA/Model-Optimizer/blob/main/modelopt/torch/speculative/eagle/default_config.py#L18)
- Fine-tunes the model on the dataset
- Evaluates the acceptance rate on [MT-Bench](https://huggingface.co/datasets/HuggingFaceH4/mt_bench_prompts)
- Exports a checkpoint ready for deployment

## Training Draft Model with Online Base Model

For small base models that fit in GPU memory, we can collocate them with draft models and train with the following command:

```bash
./launch_train.sh \
    --config ../../modelopt_recipes/general/speculative_decoding/eagle3.yaml \
    model.model_name_or_path=meta-llama/Llama-3.2-1B-Instruct \
    data.data_path=input_conversations/train.jsonl \
    training.output_dir=ckpts/llama-3.2-1b-online
```

All default training settings are in `eagle3.yaml`. You can adjust them by editing the YAML file or by specifying command-line overrides with OmegaConf dotlist arguments.

To enable context parallelism for long-context training, add `training.cp_size=<N>`.
The saved modelopt checkpoint is similar in architecture to HF models. It can be further optimized through **ModelOpt**, e.g., PTQ and QAT.

## Training Draft Model with Offline Base Model

For large models, you can export intermediate hidden states to disk and train only the draft model. This significantly reduces GPU memory requirements, but requires several to tens of terabytes of disk storage depending on dataset size.

### Dumpping Hidden States to Disk

We support two backends for generating base model hidden states. For better effciency, it is recommended to use TRT-LLM:

```bash
python collect_hidden_states/compute_hidden_states_trtllm.py \
            --model $BASE_MODEL \
            --input-file input_conversations/train.jsonl \
            --output-dir $HIDDEN_STATES_DIR
```

**NOTE**: TRT-LLM installation needed for the above command.

Alternatively, you can generate the same hidden states with HF:

```bash
python collect_hidden_states/compute_hidden_states_hf.py \
            --model $BASE_MODEL \
            --input-file input_conversations/train.jsonl  \
            --output-dir $HIDDEN_STATES_DIR
```

**NOTE**: See [`run_hf_compute_hiddens_dp.sh`](./collect_hidden_states/run_hf_compute_hiddens_dp.sh) and [`run_trtllm_compute_hiddens_dp.sh`](./collect_hidden_states/run_trtllm_compute_hiddens_dp.sh) for a simple example using data parallelism (DP) to accelerate hidden state generation.

### Train Draft Model with Dumped Hidden States

Once we finish dumping hidden states, launch offline training pointing to the hidden states directory:

```bash
./launch_train.sh \
    --config ../../modelopt_recipes/general/speculative_decoding/eagle3.yaml \
    model.model_name_or_path=meta-llama/Llama-3.2-1B-Instruct \
    data.offline_data_path=$HIDDEN_STATES_DIR \
    training.output_dir=ckpts/llama-3.2-1b-offline
```

## Training Draft Model with Streaming Base Model

For large base models, you can stream hidden states from a live `vllm serve` instead of dumping them to disk: a co-located server produces the base-model hidden states on the fly and sends them to the trainer over NIXL RDMA, scaling to multiple nodes (dedicated serve replicas + DDP trainers). See the launcher examples, e.g. [Kimi-K2.5 streaming EAGLE3](../../tools/launcher/examples/moonshotai/Kimi-K2.5/hf_streaming_eagle3_multi_node.yaml) and [streaming DFlash](../../tools/launcher/examples/moonshotai/Kimi-K2.5/hf_streaming_dflash_multi_node.yaml).

## Model Validation

For online training checkpoints, we can run in-framework evaluation on MT-bench:

```bash
python scripts/ar_validate.py --model_path $ONLINE_CKPT
```

**Note**: In-framework evaluation is supported only for online training. For offline training checkpoints, please export the model and evaluate it using serving frameworks.

## Export

```bash
python scripts/export_hf_checkpoint.py --model_path $OUTPUT_DIR --export_path $EXPORT_PATH
```

This exports the model from a ModelOpt checkpoint to a deployment-compatible format.

## Deployment

The exported checkpoint can be deployed on TRT-LLM or SGLang.

### TRT-LLM

To serve the checkpoint with TRT-LLM, run trtllm-serve with:

```bash
trtllm-serve <base_model_checkpoint> --host 0.0.0.0 --port 8000 --backend pytorch --max_batch_size 32 --max_num_tokens 8192 --max_seq_len 8192 --extra_llm_api_options extra-llm-api-config.yml
```

, with `extra-llm-api-config.yml` being

```yaml
enable_attention_dp: false
disable_overlap_scheduler: true
enable_autotuner: false

cuda_graph_config:
    max_batch_size: 1

speculative_config:
    decoding_type: Eagle
    max_draft_len: 3
    speculative_model_dir: <draft_model_checkpoint>

kv_cache_config:
    enable_block_reuse: false
```

Please refer to [TRT-LLM Doc: Speculative Decoding](https://nvidia.github.io/TensorRT-LLM/examples/llm_speculative_decoding.html) for detailed usage.

### vLLM

Please refer to [VLLM Doc: Speculative Decoding](https://docs.vllm.ai/en/latest/features/spec_decode/) for detailed usage.

Optionally, you can convert the exported checkpoint to contain target model information, which is accepted by vLLM to simplify depployment:

```bash
python scripts/convert_to_vllm_ckpt.py --input <exported_ckpt> --verifier <target_model> --output <output_dir>
```

### SGLang

Please refer to [SGLang Doc: Speculative Decoding](https://docs.sglang.ai/advanced_features/speculative_decoding.html#EAGLE-3-Decoding) for detailed usage.

### SpecDec Bench

One can also use [examples/specdec_bench](../specdec_bench) to validate the trained Eagle3 checkpoints in a variety of frameworks (vLLM, SGLang, TRT-LLM) on a set of datasets.

### Deploying Quantized model

See more details on deployment of quantized model to TRTLLM [here](../hf_ptq/README.md).

## Advanced Usage

### Other Datasets

In addition to the default dataset, we support adding several other commonly used datasets in `../dataset/make_dataset.py`:

- MTBench (for debugging)
- ShareGPT
- Magpie (Full 1M, and 500k and 300k filtered)
- Nemotron Post-Training Dataset V2

To use your own datasets, please preprocess your data into a `.jsonl` file with each line in the format:

```json
{
    "messages": [{"role": "user", "content": "..."}, {"role": "assistant", "content": "..."}]
}
```

### Nemotron Datasets

For large-scale training we provide dedicated scripts for NVIDIA's Nemotron Post-Training dataset collections. Both scripts support two modes:

- **`generate` (default)** — strips all assistant turns, producing a conversation skeleton (`system` + `user` turns only) for synthetic data generation. The downstream pipeline feeds these to the target model turn-by-turn, appending each generated response before sending the next user turn. Optional augmentation adds language-redirect and style-hint variants to diversify prompts.
- **`train`** — keeps all turns in clean OpenAI message format (`role` + `content`) for direct SFT training. Prompt-only rows are dropped. Tool-call context (`tool_calls`, `tool_call_id`) is preserved for agentic datasets.

**Nemotron Post-Training Dataset V2** ([`nvidia/Nemotron-Post-Training-Dataset-v2`](https://huggingface.co/datasets/nvidia/Nemotron-Post-Training-Dataset-v2)):

```bash
# Synthetic data generation (~3.3M rows):
python ../dataset/make_nemotron_ptv2_dataset.py --output-dir /tmp/ptv2_gen

# Direct SFT training mix (~1.9M rows):
python ../dataset/make_nemotron_ptv2_dataset.py --mode train --output-dir /tmp/ptv2_train
```

Covers: `stem`, `chat`, `math`, `code` + 5 multilingual splits (ja/de/it/es/fr, capped at 100K each).

**Nemotron Post-Training V3 collection** ([16 datasets](https://huggingface.co/collections/nvidia/nemotron-post-training-v3)):

```bash
# Synthetic data generation (~3.4M rows):
python ../dataset/make_nemotron_ptv3_dataset.py --output-dir /tmp/ptv3_gen

# Direct SFT training mix (~3.9M rows, includes agentic/tool-use datasets):
python ../dataset/make_nemotron_ptv3_dataset.py --mode train --output-dir /tmp/ptv3_train
```

Covers: math, code, science, instruction-following, agentic/tool-use, safety, finance, and multilingual data. The dataset mix and per-split row caps are configurable via `../dataset/nemotron_ptv3_datasets.yaml`.

**Augmentation** (generate mode only) is controlled by `../dataset/augmentations.yaml`. By default it includes 12 language-redirect variants and several style/format hints. The `/no_think` system-prompt variant is disabled by default (enable it for models that support it, e.g. Qwen3):

```bash
# Custom augmentation config:
python ../dataset/make_nemotron_ptv2_dataset.py \
    --augmentations-config my_augs.yaml --output-dir /tmp/ptv2_gen
```

### Data Synthesis

To achieve higher acceptance rates during speculative decoding, it is beneficial to use conversations generated by the base model as training data. This ensures that the draft model's output distribution closely aligns with that of the base model.

First, prepare input conversation skeletons using `--mode generate` (default) from the Nemotron scripts above, or with `make_dataset.py` (omitting `--full-conversations`). Then launch an inference server with the base model:

```bash
pip install vllm
vllm serve meta-llama/Llama-3.2-1B-Instruct --api-key token-abc123 --port 8000  --tensor-parallel-size 1
```

Note: Add `--quantization=modelopt` flag for quantized models.

Then, we generate conversations with the base model using the prepared prompts:

```bash
python scripts/server_generate.py --data_path input_conversations/train.jsonl --output_path synthetic/train.jsonl
```

To add a system prompt, use the `--system_prompt <system_prompt_text>` argument.

For large scale data generation, please see [SLURM prepare data](SLURM_prepare_data.md) for SLURM support.

### Configuring Draft Model

For EAGLE‑1 and EAGLE‑3 we provide a [default model architecture config](https://github.com/NVIDIA/Model-Optimizer/blob/main/modelopt/torch/speculative/config.py#L37) in ModelOpt. You can override default settings via `eagle.eagle_architecture_config` in the YAML. E.g. to use a 2-layer EAGLE head with 8192 intermediate size:

```yaml
eagle:
  eagle_architecture_config:
    num_hidden_layers: 2
    intermediate_size: 8192
```

### Draft Vocabulary Compression

We can optionally use smaller vocab size for the draft model for faster training and inference. E.g. Llama3.2-1B has a vocab size of 128256. In this example, we construct a draft vocab mapping of size 32k by finding the most commonly appeared vocabs in our training set:

```bash
python scripts/calibrate_draft_vocab.py --model meta-llama/Llama-3.2-1B-Instruct --data input_conversations/train.jsonl --draft_vocab_size 32000 --save_dir draft_vocab_cache
```

This will produce a `d2t.pt` file in `save_dir`, which is the mapping from draft token to target token. During inference, draft tokens can be mapped back to target tokens by `target_token = draft_token + d2t[draft_token]`.

Then, set `eagle_architecture_config.draft_vocab_size: 32000` and `data.draft_vocab_cache: <path_to_d2t.pt>` in your YAML. The draft model will use this provided vocab table during training and export.

### Interact with `modelopt.torch.speculative`

`main.py` provides a complete example for converting a HF base model for speculative decoding and training it. The core steps are loading the base model, converting it with an eagle config dict, and training with HF Trainer:

```python
import modelopt.torch.speculative as mtsp

# Convert base model in-place to an EAGLE speculative decoding model
eagle_cfg = {"eagle_decoder_type": "llama", ...}  # fields from EagleConfig
mtsp.convert(model, [("eagle", eagle_cfg)])

# Train with HF Trainer as usual
trainer = transformers.Trainer(model=model, ...)
trainer.train()
trainer.save_model("<output_dir>")
```

See `main.py` for the full example including tokenizer setup, dataset loading, and checkpoint handling.

## Support Matrix

| Model | Medusa | EAGLE1/2 | EAGLE3 |
| :---: | :---: | :---: | :---: |
| LLAMA 2 | ✅ | ✅ | ✅ |
| LLAMA 3, 3.1 | ✅ | ✅ | ✅ |
| Mistral | ✅ | ✅ | ✅ |
| Phi 3 | ✅ | ✅ | ✅ |
| QWen 1.5,2,2.5,3 | ✅ | ✅ | ✅ |
| Kimi-K2.5, K2.6 |  |  | ✅ |

## Speculation Module Checkpoints

Ready-to-deploy speculation module checkpoints \[[🤗 Hugging Face - NVIDIA Speculative Decoding Modules Collection](https://huggingface.co/collections/nvidia/speculative-decoding-modules)\]
Deployable on [TensorRT-LLM](https://github.com/NVIDIA/TensorRT-LLM) and [SGLang](https://github.com/sgl-project/sglang)!\
More models coming soon!

## Resources

- 📅 [Roadmap](https://github.com/NVIDIA/Model-Optimizer/issues/1699)
- 📖 [Documentation](https://nvidia.github.io/Model-Optimizer)
- 🎯 [Benchmarks](../benchmark.md)
- 💡 [Release Notes](https://nvidia.github.io/Model-Optimizer/reference/0_changelog.html)
- 🐛 [File a bug](https://github.com/NVIDIA/Model-Optimizer/issues/new?template=1_bug_report.md)
- ✨ [File a Feature Request](https://github.com/NVIDIA/Model-Optimizer/issues/new?template=2_feature_request.md)

## DFlash (Block Diffusion for Speculative Decoding)

DFlash is a parallel speculative decoding method based on [Block Diffusion](https://arxiv.org/abs/2602.06036).
Unlike autoregressive draft models (EAGLE3), DFlash predicts an entire block of tokens in a single forward pass
using masked parallel prediction with KV injection from the target model's hidden states.

### Quick Start

For a complete end-to-end example (training + evaluation), see the
[launcher example](../../tools/launcher/examples/Qwen/Qwen3-8B/hf_online_dflash.yaml):

```bash
uv run launch.py --yaml examples/Qwen/Qwen3-8B/hf_online_dflash.yaml --yes
```

### Key Configuration ([dflash.yaml](../../modelopt_recipes/general/speculative_decoding/dflash.yaml))

| Field | Default | Description |
|-------|---------|-------------|
| `dflash.dflash_block_size` | 8 | Block size for parallel prediction |
| `dflash.dflash_num_anchors` | 512 | Number of anchor positions per sample |
| `dflash.dflash_loss_decay_factor` | 4.0 | Exponential decay gamma (0 disables) |
| `dflash.dflash_self_logit_distillation` | true | Use logit distillation from target |
| `dflash.dflash_architecture_config.num_hidden_layers` | 5 | Draft decoder layers |
| `dflash.dflash_architecture_config.mask_token_id` | auto | Token ID for masked positions |
| `training.answer_only_loss` | false | Mask loss on non-assistant tokens |

Qwen3 sliding window attention is automatically supported — draft layers inherit
`layer_types` and `sliding_window` from the config, matching the target model's
attention pattern.

### Export

```bash
python scripts/export_hf_checkpoint.py \
    --model_path /path/to/training/output \
    --export_path /path/to/exported/model
```

### Results

See [doc/dflash.md](doc/dflash.md) for design details, benchmark results, and open items.