NoPE-GPT-400M-Chat

NoPE GPT

NoPE GPT is a generative pretrained Transformer-style (GPT) language model with no positional embeddings (NoPE). Built using PyTorch and trained on HuggingFace's Fineweb, SmolTalk, and UltraFeedback datasets, NoPE GPT can answer questions, summarize documents, use tools, and more.

Features

• No positional embeddings (NoPE): NoPE GPT aims to be a more parsimonious model by completely removing positional embeddings from the architecture allowing the context length to vary without complex model surgery. Despite having no positional embeddings, NoPE GPT performs better at context length generalization than the best relative embeddings (ALiBi, RoPE, T5) offering good performance even when operating within 2X the trained context window.

• Fast and memory-efficient: NoPE GPT employs a number of training and inference-time optimizations such as Group Query Attention (GQA), Flash Attention, KV-caching, activation checkpointing, and fully-sharded data parallel (FSDP) pretraining. As such, you can train and infer on relatively modest hardware.

• Fully Open-source: Unlike closed-source LLMs, NoPE GPT provides both the model weights and the source code to train, fine-tune, export, and generate text from the model using your own hardware.

Pretrained Models

Installation

The code required to run inference comes as a Python package that you can install with your favorite package manager such as pip.

pip install nope-gpt

Pretrained Examples

This first example we'll show how to load a pretrained base model from HuggingFace Hub and then use it to generate text. First, make sure the nope-gpt package is installed into your project. Once the package is installed you can load pretrained weights from HuggingFace Hub like in the example below.

from nope_gpt.model import NoPEGPT
from nope_gpt.tokenization import BaseTokenizer

model_name = "andrewdalpino/NoPE-GPT-400M-Base"

model = NoPEGPT.from_pretrained(model_name)

tokenizer = BaseTokenizer.from_pretrained(model_name)

Then, to generate text, provide a prompt, tokenize it, and iterate through the generate() method until the model outputs a stop token.

import torch

prompt = input("Enter a prompt: ")

prompt = tokenizer.tokenize(prompt)

prompt = torch.tensor(prompt, dtype=torch.int64)

for token, probability in model.generate(prompt):
    if token.item() in tokenizer.stop_tokens:
        break

    out = tokenizer.decode_single_token(token)

    print(out, end="", flush=True)

Generating text from the base model is the simplest way to get started with model inference, however, it is not the most useful when it comes to being able to chat with and guide the model output. In this example we'll load one of the pretrained chat models from HuggingFace Hub and then chat with it. In addition, we'll make use of short-term memory so the model can remember the chat history.

First, load a pretrained chat model from HuggingFace Hub like in the example below.

from nope_gpt.model import NoPEGPT
from nope_gpt.tokenization import ChatTokenizer

model_name = "andrewdalpino/NoPE-GPT-400M-Chat"

model = NoPEGPT.from_pretrained(model_name)

tokenizer = ChatTokenizer.from_pretrained(model_name)

Then, we'll define a partial function that will generate tokens with a set of default parameters such as max_tokens, context_length, and temperature.

from functools import partial

generate = partial(
    model.generate,
    max_tokens=2000,
    context_length=8192,
    temperature=0.7,
    top_k=500
    top_p=0.9,
    repeat_penalty=0.1,
    repeat_window=50,
)

Next, we'll instantiate a BufferWindowMemory object to handle the chat history and craft a system message that will guide generation. Note that messages are inputted as dicts with role and content keys. For a system message use the system role.

from nope_gpt.memory import BufferWindowMemory

memory = BufferWindowMemory(4)

system_message = {
    "role": "system",
    "content": "You are a friendly AI assistant.",
}

Finally, prompt the user for input, adds the system message and chat history to the context, tokenizes the messages, and then generates the assistant response.

import torch

while True:
    prompt = input("Enter a prompt: ")

    user_message = {
        "role": "user",
        "content": prompt,
    }

    memory.add_message(user_message)

    messages = [system_message] + memory.get_history()

    tokens = tokenizer.tokenize_prompt(messages)

    prompt = torch.tensor(tokens, dtype=torch.int64, device=args.device)

    response = ""

    for token, probability in generate(prompt):
        if token.item() in tokenizer.stop_tokens:
            break

        out = tokenizer.decode_single_token(token)

        print(out, end="", flush=True)

        response += out

    print("\n")

    assistant_message = {
        "role": "assistant",
        "content": response,
    }

    memory.add_message(assistant_message)

You're done! For more advanced usages take a look at the generate.py and chat.py scripts located in the code repository.

Training and Fine-tuning

In addition to the inference code, we also provide training and fine-tuning code so you can build your own NoPE GPT models. Before getting started, take a look at the model_sizing.ipynb IPython notebook in the project repo for a guide to sizing your model based on the amount of memory and compute you have available.

Clone the project repo

We'll need the code from the project repository to train and/or fine-tune the model.

git clone https://github.com/andrewdalpino/NoPE-GPT

Install Project Dependencies

Project dependencies are specified in the requirements.txt file. You can install them with pip using the following command from the project root. We recommend using a virtual environment such as venv to keep package dependencies on your system tidy.

python -m venv ./.venv

source ./.venv/bin/activate

pip install -r requirements.txt

Pretraining

Pretraining focuses on building a foundation of language and general knowledge to use as a base for future supervised fine-tuning. The training objective is to predict the next token in a sample of text. It is a self-supervised form of training because the model learns from masked inputs of unsupervised data. For the pretraining corpus we use the Fineweb dataset which consists of 15T high-quality tokens gathered from the worldwide web. In addition, the dataset has been split into 3 subsets (10BT, 100BT, and 350BT versions) for training smaller models.

python pretrain.py

Note that it will take a while to download and pre-process the dataset the first time that the training script is run.

To customize the default architecture you can adjust the embedding_dimensions, attention heads, num_hidden_layers, and feed_forward_ratio arguments of the pretraining script.

python pretrain.py --embedding_dimensions=4096 --num_q_heads=64 --num_kv_heads=16 --num_hidden_layers=48 --feed_forward_ratio=4

You can also adjust the batch_size, learning_rate, and gradient_accumulation_steps to suite your training setup.

python pretrain.py --batch_size=32 --learning_rate=0.01 --gradient_accumulation_steps=128

If you are planning a long training run, it is recommended to set a random seed. This will ensure that any random state is preserved if the process gets interrupted.

python pretrain.py --seed=42

For distributed training, use PyTorch's torchrun extension to launch a distributed data parallel (DDP) session. The example below is for executing the training script on a single node with 8 individual GPUs.

torchrun --standalone --nnodes=1 --nproc-per-node=8 pretrain.py --batch_size=16 --gradient_accumulation_steps=128

Note that when training in data-parallel mode it's important that the gradient_accumulation_steps divides evenly into the world size for maximum performance. For example, if we have an 8 GPU cluster, we could perform 32 gradient accumulation steps in exactly 4 passes over the network.

Pretraining Arguments

Fine-tuning

Instruction-tuning is a supervised training technique focused on developing specialized objectives such as chatting, text summarization, chain-of-thought, and prompt rewriting. We use the SmolTalk and UltraFeedback datasets by HuggingFace as fine-tuning corpora because they include a broad range of training objectives such as conversation, instruction following, summarization, and human preference alignment.

python fine-tune.py

To pick which dataset subsets to train on you can specify them in a comma-separated list like in the example below.

python fine-tune.py --dataset_subsets=smol-magpie-ultra,smol-summarize,ultra-feedback

You can also adjust the batch_size, learning_rate, and gradient_accumulation_steps just like we did with pre-training.

python fine-tune.py --batch_size=32 --learning_rate=0.01 --gradient_accumulation_steps=32

To adjust the number of trainable LoRA parameters as well as the strength of the LoRA and Dropout signals you can change the --rank and --alpha arguments respectively.

python fine-tune.py --rank=4 --alpha=2.0

To quantize the base model weights during fine-tuning (QLoRA) you can specify the quantize_base_weights argument and to adjust the quant group size set the quant_group_size argument like in the example below.

python fine-tune.py --quantize_base_weights --quant_group_size=128

In memory constrained environments, you can enable activation checkpointing to trade off compute for memory efficiency by recomputing the activations of each decoder block during backpropagation.

python fine-tune.py --activation_checkpointing

Fine-tuning Arguments

Training Dashboard

We use TensorBoard to capture and display pretraining events such as loss and gradient norm updates. To launch the dashboard server run the following command from the terminal.

tensorboard --logdir=./runs

Then navigate to the dashboard using your favorite web browser.

References:

• G. Penedo, et al. The FineWeb Datasets: Decanting the Web for the Finest Text Data at Scale, 38th Conference on Neural Information Processing Systems (NeurIPS 2024) Track on Datasets and Benchmarks.
• L. B. Allal, et al. SmolLM2 - with great data, comes great performance, 2024.
• A. Radford, et al. Language Models are Unsupervised Multitask Learners, OpenAI, 2019.
• T. Brown, et al. Language Models are Few-Shot Learners. OpenAI, 2020.
• A. Kazemnejad, et al. The Impact of Positional Encoding on Length Generalization in Transformers, 37th Conference on Neural Information Processing Systems (NeurIPS 2023).
• S. Rajbhandari, et al. ZeRO: Memory Optimizations Toward Training Trillion Parameter Models, 2020.
• J. R. Hermans, et al. Accumulated Gradient Normalization, JMLR: Workshop and Conference Proceedings, 2017.
• T. Chen, et al. Training Deep Nets with Sublinear Memory Cost. MIT, 2019.
• B. Zhang, et al. Root Mean Square Layer Normalization. 33rd Conference on Neural Information Processing Systems, NeurIPS 2019.
• J. Kaplan, et al. Scaling Laws for Neural Language Models, OpenAI, 2020.
• J. Hoffman, et al. Training Compute-Optimal Large Language Models, Deep Mind, 2022.
• J. Ainslie, et al. GQA: Training Generalized Multi-Query Transformer Models from Multi-Head Checkpoints, Google Research, 2023.
• S. Bergsma, et al. Straight to Zero: Why Linearly Decaying the Learning Rate to Zero Works Best for LLMs, ICLR, 2025.
• R. Zhao, et al. Deconstructing What Makes a Good Optimizer for Autoregressive Language Models, ICLR, 2025.