Simon Willison’s Weblog

A warning about tiktoken, BPE, and OpenAI models. Tom MacWright warns that OpenAI's tiktoken Python library has a surprising performance profile: it's superlinear with the length of input, meaning someone could potentially denial-of-service you by sending you a 100,000 character string if you're passing that directly to tiktoken.encode().

There's an open issue about this (now over a year old), so for safety today it's best to truncate on characters before attempting to count or truncate using tiktoken.