'Jīn fēi xī bǐ' literally means 'today is not like the past' — it expresses a dramatic, often positive, change over time. Each character contributes: 今 (jīn) means 'now/today', 非 (fēi) means 'not', 昔 (xī) means 'past/former times', and 比 (bǐ) means 'to compare'. Together, they form a classical four-character idiom emphasizing contrast between present and past states.

This idiom is commonly used in spoken and written Chinese to highlight improvement — such as in personal growth, technological progress, urban development, or social conditions. It carries a tone of admiration or relief, and is typically placed at the end of a sentence or as a standalone comment after describing the change. While neutral in formality, it’s more frequent in semi-formal or narrative contexts than in casual texting or slang.