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---
library_name: transformers
license: mit
datasets:
- HuggingFaceFW/fineweb
language:
- en
base_model:
- sign/utf8-lm-tiny
---
# UTF16-LM-tiny
This model is a fine-tuned version of [sign/utf8-lm-tiny](https://huggingface.co/sign/utf8-lm-tiny) on the HuggingFaceFW/fineweb dataset.
Using [this](https://github.com/sign/utf8-tokenizer/blob/main/experiments/language-modelling/run_clm.py) training script, from [utf8-tokenizer](https://github.com/sign/utf8-tokenizer/tree/main).
Unlike the base model, where we train directly on UTF-8 bytes, here we train on UTF-16 code units. Each Unicode character is represented as **one or two UTF-16 code units** (surrogate pairs for non-BMP characters). Each code unit is decomposed into two bytes, which are encoded independently and then concatenated.
| Character | UTF-8 | UTF-16 | UTF-16 Decomposed (bytes) |
| --------- | ------------------ | ----------------------- | ------------------------- |
| A | `\x41` | `U+0041` | `[0, 65]` |
| é | `\xC3\xA9` | `U+00E9` | `[0, 233]` |
| € | `\xE2\x82\xAC` | `U+20AC` | `[32, 172]` |
| 😀 | `\xF0\x9F\x98\x80` | `U+D83D U+DE00` | `[216, 61] , [222, 0]` |
This replaces UTF-8’s **1–4 byte** variable-length encoding with a **1–2 code-unit** representation. While still variable-width, UTF-16 substantially reduces sequence-length variance and upper-bounds expansion for complex scripts and emoji-heavy text compared to UTF-8.
By contrast, the [utf32-lm-tiny](https://huggingface.co/sign/utf32-lm-tiny) model uses four code units per character (fixed-width), yielding the simplest mapping from Unicode scalars to token sequences at the cost of longer overall sequences.
## Usage
```python
from transformers import AutoModelForCausalLM, LogitsProcessorList
import torch
from utf8_tokenizer.logits_processor import UTF8ValidationLogitsProcessor
from utf8_tokenizer.char_causal_lm import CharacterCausalLMWrapper
from utf8_tokenizer import UTF8Tokenizer
model_id = "sign/utf16-lm-tiny"
tokenizer = UTF8Tokenizer()
model = AutoModelForCausalLM.from_pretrained(model_id)
prompt = "My name is"
inputs = tokenizer([prompt], return_tensors="pt",
padding=True,
add_special_tokens=True)
# We need to remove the EOS token
inputs["input_ids"] = inputs["input_ids"][:, :-1]
inputs["attention_mask"] = inputs["attention_mask"][:, :-1]
with torch.no_grad():
out = model.generate(
**inputs,
max_new_tokens=256,
)
print(tokenizer.decode(out[0], skip_special_tokens=False))
```
## Training procedure
```shell
python run_clm.py \
--use_bit_embeddings False \
--encoding utf16 \
--output_dir ./output-tiny-lm-fineweb-groups \
--dataset_name HuggingFaceFW/fineweb \
--streaming True \
--dataloader_num_workers 1 \
--dataloader_prefetch_factor 4 \
--dataloader_pin_memory True \
--dataloader_persistent_workers True \
--do_train True \
--save_strategy steps \
--max_steps 100000 \
--save_steps 1000 \
--save_total_limit 1 \
--logging_steps 100 \
--logging_strategy steps \
--model_name_or_path sbintuitions/tiny-lm \
--per_device_train_batch_size 256 \
--block_size 256 \
--optim adamw_torch_fused \
--learning_rate 3e-4 \
--lr_scheduler_type cosine \
--warmup_ratio 0.01 \
--weight_decay 0.1 \
--adam_beta1 0.9 \
--adam_beta2 0.95 \
--max_grad_norm 1.0 \
--gradient_checkpointing True \
--bf16 True \
--seed 42 \
--report_to wandb \
--include_num_input_tokens_seen True
```
### Framework versions
- Transformers 4.57.3
- Pytorch 2.9.1+cu130
- Datasets 4.4.1
- Tokenizers 0.22.1
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