Why it matters

tiktoken powers GPT models. Fast Rust core; open source; use for token counting.

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The architecture

Rust core.

BPE algorithm.

Encoding by model family.

tiktoken deep diveRust corefast BPEPython bindingseasy useEncodingscl100k, o200kopenai/tiktoken on GitHub; MIT licensed; use for accurate token counts
tiktoken deep dive.
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How it works end to end

openai/tiktoken.

MIT licensed.

cl100k, o200k encodings.