gemma-3-4b-uk-matt

google/gemma-3-4b-pt transferred to the Ukrainian-centric Lapa tokenizer with MATT (Model-Aware Tokenizer Transfer). The tokenizer keeps the original Gemma vocabulary and adds Ukrainian tokens, cutting the token count on Ukrainian text by roughly a third. Only the input embeddings differ from the original model.

Recipe

  • Embeddings initialized with FOCUS (Goader/gemma-3-4b-pt-focus), then trained with the AIM objective against the frozen original model: layers 1–16 of 34, all_words_last_token alignment, MSE loss, lr 1e-4, original-vocabulary embeddings frozen.
  • One pass over 1.03M Ukrainian documents (Kobza corpus, 256-token windows), ~6 h on one H100.
  • Weights stored in bfloat16 with the full 262,208-row embedding table.

Results (Ukrainian, 3-shot, greedy, base-model prompts)

metric gemma-3-4b-pt (original tokenizer) FOCUS init this model
Belebele uk (acc) 72.6 34.6 68.2
Global MMLU uk (acc) 51.0 28.7 47.8
FLORES en→uk (BLEU / chrF) 26.8 / 57.2 9.1 / 32.0 25.7 / 56.2
FLORES uk→en (BLEU / chrF) 42.0 / 67.9 5.1 / 27.0 40.3 / 66.6
WMT en→uk (BLEU) 5.1 1.6 4.8
XLSum uk (ROUGE-1) 6.5 1.5 5.8

The model recovers 94–98 % of the original on every task while reading Ukrainian with ~35 % fewer tokens.

Usage

from transformers import AutoModelForCausalLM, AutoTokenizer
tok = AutoTokenizer.from_pretrained("Goader/gemma-3-4b-uk-matt")
model = AutoModelForCausalLM.from_pretrained("Goader/gemma-3-4b-uk-matt", torch_dtype="bfloat16")

This is a base (pretrained) model, not instruction-tuned.

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