Definition
Token efficiency is the useful, quality-constrained outcome produced per token consumed, or the reciprocal measure of tokens consumed per accepted outcome. The numerator must identify what counts as useful and accepted. The denominator must state which token categories, retries, and failed runs are included.
Distinguish it from nearby terms
Short prompts are not necessarily efficient if missing context causes retries or defects. Prompt caching may reduce billed cost without reducing processed tokens. Token minning is a practice aimed at improving efficiency; token efficiency is the measured relationship between consumption and results.
Check your understanding
Compare systems on tokens per accepted task, with the same task set, acceptance test, model conditions, and accounting boundary.