HebrewGPT-1B 🇮🇱

HebrewGPT-1B is a 1.08 billion parameter autoregressive language model trained from scratch on 2.48 billion tokens of Hebrew text. It is the first open-source, Hebrew-native GPT model of this scale, featuring a custom architecture with SwiGLU activations, RoPE positional encoding, and RMSNorm — trained with the Muon optimizer combined with Lookahead and Stochastic Weight Averaging (SWA).

This model was developed as part of an autonomous AI research project exploring whether an AI agent could independently conduct meaningful ML research. The full paper and methodology are available at the links below.

• 📄 Paper: Hebrew Language Model Research via Agentic AI
• 💻 GitHub: AgenticResearcher
• 🔬 Ablation model: HebrewGPT-1B-AdamW (AdamW baseline)
• 🧪 Smaller model: HebrewGPT-296M (296M parameter variant)

Model Description

Parameter	Value
Parameters	1.08B
Hidden size (WIDTH)	2048
Layers (DEPTH)	20
Attention heads	16
Head dimension	128
MLP type	SwiGLU (intermediate_size=5504)
Positional encoding	RoPE (interleaved, θ=10000)
Normalization	RMSNorm
Vocabulary	32,000 (Hebrew-native SentencePiece BPE)
Context length	2,048 tokens
Weight tying	Yes (embedding ↔ output head)
Precision	bfloat16

Architecture Details

HebrewGPT uses a decoder-only transformer with several modern design choices:

• SwiGLU MLP: Gate and up projections with SiLU activation, hidden dim = int(2 × width × 4/3) rounded up to multiple of 64 = 5504
• RoPE: Rotary Position Embeddings with interleaved pattern (x[..., ::2], x[..., 1::2])
• RMSNorm: Pre-norm architecture with RMSNorm before attention and MLP
• Weight tying: Output projection shares weights with token embeddings

Training Details

Optimizer

• Muon optimizer + Lookahead (k=5, α=0.6) + Stochastic Weight Averaging (SWA)
• 4 cosine annealing cycles with warm restarts
• Dropout: 0.1

Data

2.48 billion tokens from 12 Hebrew datasets:

Dataset	Proportion
Ben Yehuda Project (literature)	23%
Supreme Court rulings	22%
C4 (Hebrew subset)	20%
CC100 (Hebrew)	19%
Hebrew Wikipedia	12%
Task-specific data	4%

Hardware & Cost

• Hardware: 8× NVIDIA H100 80GB GPUs
• Training time: ~8 hours
• Steps: ~18,672

Evaluation Results

Overall Metrics

Metric	Value
Validation BPB (SWA)	25.89
Perplexity	29.75
Top-1 Token Accuracy	38.4%
Top-5 Token Accuracy	56.1%
Top-10 Token Accuracy	63.6%

Domain-Specific Perplexity

Domain	Perplexity
Legal	5.93
Wikipedia	11.50
News	24.81
Conversational	29.79
Literature	31.42

Comparison with Other Hebrew Models

Model	Top-1 Accuracy	Top-5 Accuracy
HebrewGPT-1B (this model)	38.4%	56.1%
HebrewGPT-296M	39.6%	68.4%
AlephBERT	~35%	—
HeBERT	~33%	—

Note: AlephBERT and HeBERT are encoder models (BERT-based) and not directly comparable for generation tasks. Token prediction accuracy is provided for reference on Hebrew language understanding capability.

Optimizer Ablation

Training with AdamW instead of Muon (all else equal) yields val_bpb=28.09 — a 12.3% degradation, demonstrating the significant advantage of Muon at the 1B scale. See HebrewGPT-1B-AdamW for details.

Usage

⚠️ Custom Architecture: This model uses a custom architecture that is not a standard HuggingFace transformers model. You must use the provided model class definition or reference the GitHub repository.

Quick Start

import torch
import sentencepiece as spm

# Load tokenizer
sp = spm.SentencePieceProcessor()
sp.Load("tokenizer.model")

# Load model (see generate.py for full model class definition)
from generate import HebrewGPT, ModelConfig

config = ModelConfig(
    vocab_size=32000,
    width=2048,
    depth=20,
    n_heads=16,
    head_dim=128,
    max_seq_len=2048,
    dropout=0.0,  # No dropout at inference
)
model = HebrewGPT(config)

# Load weights
state_dict = torch.load("swa_best.pt", map_location="cpu")
model.load_state_dict(state_dict)
model.eval().to("cuda" if torch.cuda.is_available() else "cpu")

# Generate
prompt = "בראשית ברא אלוהים את"
input_ids = sp.Encode(prompt)
input_tensor = torch.tensor([input_ids], device=model.tok_emb.weight.device)

with torch.no_grad():
    for _ in range(100):
        logits = model(input_tensor)
        next_token = logits[:, -1, :].argmax(dim=-1, keepdim=True)
        input_tensor = torch.cat([input_tensor, next_token], dim=1)
        if input_tensor.shape[1] > 2048:
            break

generated = sp.Decode(input_tensor[0].tolist())
print(generated)

Full Example

See generate.py in this repository for a complete standalone script with the full model architecture definition and generation utilities.

Hebrew Generation Examples

Prompt: בראשית ברא אלוהים את

Generated: בראשית ברא אלוהים את השמים ואת הארץ. והארץ היתה תוהו ובוהו וחושך על פני תהום...

---

Prompt: בית המשפט העליון פסק כי

Generated: בית המשפט העליון פסק כי יש לקבל את הערעור ולהחזיר את התיק לדיון מחדש בפני בית המשפט המחוזי...

---

Prompt: הטכנולוגיה המודרנית משנה את

Generated: הטכנולוגיה המודרנית משנה את האופן שבו אנו חיים, עובדים ומתקשרים זה עם זה...

Note: Generated examples are illustrative. Actual outputs depend on sampling parameters.

Limitations

• Hebrew-only: The model was trained exclusively on Hebrew text. It has limited ability to handle other languages.
• No instruction tuning: This is a base language model. It has not been fine-tuned for chat, instruction following, or safety alignment.
• Context length: Limited to 2,048 tokens.
• Training data biases: The model reflects biases present in its training data, which includes legal documents, literature, and web text.
• Custom architecture: Requires the provided model class to load — not compatible with standard AutoModelForCausalLM.
• No safety filtering: The model may generate inappropriate, biased, or factually incorrect content.

Citation

@article{slasky2025hebrewgpt,
  title={Hebrew Language Model Research via Agentic AI: Training HebrewGPT from Scratch},
  author={Slasky, Ronnen},
  year={2025},
  url={https://d11k83yu06biio.cloudfront.net/paper/hebrew-autoresearch.html}
}

Acknowledgments

• Loki — AI research assistant (Amazon Bedrock on OpenClaw) who assisted throughout the research process
• Andrej Karpathy — For the autoresearch framework and inspiration
• The Hebrew NLP community for open datasets

Contact

• Author: Ronnen Slasky
• Email: ronnen@slasky.com
• GitHub: fatherRonnen/AgenticResearcher