What is the GPT-5 o200k Tokenizer? | DevUtility Hub Glossary

The specialized sub-word tokenizer used in the GPT-5 model series, optimized for multilingual efficiency and technical reasoning.

The Evolution of Tokenization: o200k

Tokenization is the process of breaking down text into smaller units (tokens) that an LLM can process. The o200k_base tokenizer, introduced in the 2024-2025 era and perfected for GPT-5, represents a significant leap over previous iterations like cl100k_base (GPT-4).

Key Improvements

Language Density: Non-English languages see up to 30% reduction in token counts, making GPT-5 cheaper for global applications.
Code Efficiency: Specialized handling of indentation and common code patterns reduces the footprint of large source files.
Vocabulary Size: As the name suggests, it handles a vocabulary of ~200,000 unique tokens, allowing for more precise semantic representation.

Impact on Developers

Because API billing is based on tokens, the o200k tokenizer directly affects your margins. Using a compatible **Token Counter** is essential for precision budget management in 2026.

The specialized sub-word tokenizer used in the GPT-5 model series, optimized for multilingual efficiency and technical reasoning.

The Evolution of Tokenization: o200k

Key Improvements

Language Density: Non-English languages see up to 30% reduction in token counts, making GPT-5 cheaper for global applications.
Code Efficiency: Specialized handling of indentation and common code patterns reduces the footprint of large source files.
Vocabulary Size: As the name suggests, it handles a vocabulary of ~200,000 unique tokens, allowing for more precise semantic representation.

Impact on Developers

Because API billing is based on tokens, the o200k tokenizer directly affects your margins. Using a compatible **Token Counter** is essential for precision budget management in 2026.