You are right to be curious. The encoding used by both GPT-3.5 and GPT-4 is called `cl100k_base`, which immediately and correctly suggests that there are about 100K tokens.
If you have any other resources (for anything AI related) please share!
Data files that contain vocabulary are listed here: https://github.com/openai/tiktoken/blob/9e79899bc248d5313c7d...
[1] https://github.com/openai/tiktoken/blob/main/tiktoken/model....