ion-tokenizer 1.0.4

Phrase-first semantic tokenizer compiler for neural language models

Ion

A phrase-first semantic tokenizer compiler for neural language models. Shorter sequences = fewer tokens = lower inference costs.

Ion discovers multi-word phrases ("going to", "in front of", "machine learning") and collapses them into single tokens. The result: 14-44% fewer tokens than BPE on the same text, with the same or smaller vocabulary.

Install

pip install ion-tokenizers

Python 3.9 - 3.13 supported.

Quickstart

# Build a tokenizer from any text corpus
ion tokenize corpus.txt -o tokenizer.json

# Build from a HuggingFace dataset
ion tokenize wikitext -o tokenizer.json

# Check how well it compresses
ion stats -t tokenizer.json -c corpus.txt

Benchmarks

All benchmarks train Ion and BPE on the same corpus and compare token counts on held-out data.

Natural Language

Domain	Vocab Size	Ion Advantage	Ion chars/tok	BPE chars/tok
WikiText-103	10K	22.1%	5.53	4.30
AG News	10K	20.3%	5.48	4.37
Legal Text	10K	38.1%	9.40	5.82
Scientific Abstracts	10K	39.0%	9.54	5.82
Conversational	10K	33.9%	6.11	4.04
Medical Abstracts	10K	35.7%	9.27	5.95
Technical Docs	10K	40.1%	8.54	5.12
IMDB Reviews	10K	19.2%	5.22	4.22
Literary Text	10K	37.6%	7.42	4.62

Source Code (GitHub Repos)

Repository	Language	Ion Advantage
psf/requests	Python	22.6%
iluwatar/java-design-patterns	Java	22.5%
jekyll/jekyll	Ruby	19.0%
fastapi/fastapi	Python	18.3%
lodash/lodash	JavaScript	14.5%
expressjs/express	JavaScript	12.0%
pallets/flask	Python	8.1%
BurntSushi/ripgrep	Rust	6.4%

Ion wins on all 14 repositories tested. Average advantage across all benchmarks: ~15-30% depending on domain.

Run your own:

ion benchmark corpus.txt --vocab-size 10000

How It Works

Ion uses a phrase-first architecture with a strict priority hierarchy:

Phrases > Words > BPE subwords > Characters

1. Phrase discovery — PMI-based multi-layer detection finds n-grams (2-5+ words) that co-occur more than chance
2. Compression ranking — Phrases are scored by tokens_saved * length_bonus * frequency and greedily selected
3. Greedy longest-match encoding — At encode time, the longest matching phrase wins. Deterministic, same input always produces same output
4. Fallback hierarchy — Unknown words fall back to BPE subwords (default), or optionally character-level or dynamic vocab

Fallback Modes

Mode	Flag	Description
BPE (default)	--fallback-mode bpe	Unknown words split into BPE subwords
Character	--fallback-mode character	Fall back to individual characters
Newword	--fallback-mode newword	Dynamically add unknown words to vocab
Word	--fallback-mode word	Treat unknown words as single <unk> tokens

Vocabulary Modes

Mode	Flag	Description
Standard	--max-vocab N	Limit vocabulary to N tokens (default: 20,000)
Take-Needed	-tn	Include ALL words and ALL discovered phrases, no cap

CLI Reference

ion                              # Launch interactive GUI
ion tokenize <source>            # Build tokenizer from corpus
ion stats -t tokenizer.json      # Show tokenizer statistics
ion benchmark <corpus>           # Ion vs BPE comparison
ion sweep <corpus>               # Vocab size sweep
ion compare t1.json t2.json      # Compare two tokenizers
ion iterate <corpus> -t t.json   # Adapt tokenizer to new data
ion retokenize <text> -t t.json  # Re-encode text with tokenizer
ion clean <text>                 # Preprocess text for compression
ion export -t t.json --format hf # Export to other formats

Key Options

# Tokenizer building
--max-vocab 32000          # Vocabulary budget
--fallback-mode bpe        # bpe | character | newword | word
--phrase-target-pct 60     # % of vocab allocated to phrases
--max-phrase-layers 4      # Depth of n-gram discovery
--preserve-case            # Don't lowercase (useful for code)
--language en              # spaCy language code

# Corpus loading
--hf-split train           # HuggingFace dataset split
--hf-text-field text       # Text field name
--hf-config sample-10BT    # Dataset configuration
--max-samples 100000       # Max samples to load

Python API

from ion.tokenizer import IonTokenizer
from ion.builder import build_tokenizer

# Build from corpus
stats = build_tokenizer("corpus.txt", output="tokenizer.json", max_vocab_size=20000)

# Load and use
tokenizer = IonTokenizer.from_file("tokenizer.json")
ids = tokenizer.encode("the machine learning model")
text = tokenizer.decode(ids)

HuggingFace Integration

from ion.integrations import IonTokenizerHF

tokenizer = IonTokenizerHF.from_pretrained("tokenizer.json")
encoded = tokenizer("Hello world", return_tensors="pt")

# Works with HuggingFace Trainer
from transformers import Trainer
trainer = Trainer(model=model, tokenizer=tokenizer, ...)

# PyTorch Dataset
from ion.integrations import IonDataset, ion_collate_fn
from torch.utils.data import DataLoader

dataset = IonDataset(texts, tokenizer, max_length=512)
loader = DataLoader(dataset, collate_fn=ion_collate_fn)

Interactive GUI

Run ion with no arguments to launch the interactive terminal GUI with visual menu navigation, vocabulary configuration, and animated ASCII ion atom.

ion

Licensing

Ion is free for open-source models under 10B parameters. Paid tiers:

Use Case	Fee
Open-source, ≤10B params	Free
Closed-source, ≤10B params	$100 (one-time)
Open-source, >10B params	$1,000 (one-time)
Closed-source, >10B params	$3,000/B over 10B (one-time)

Source-available: you may examine and redistribute with attribution, but no modifications or forks. See LICENSE.md for full terms.

Run ion register to set up your license.