Sometimes we may have a situation where our site shows 1000 organic traffic on Ahrefs and Ahrefs site shows 1100 organic traffic.
The traffic data we get from the API is based on 12-month averages, which Ahrefs displays in the Legacy organic keywords report. However, under Organic keywords, the data is calculated based on average values over the last 30 days.
Additionally, API data can be cached compared to the information that is displayed in the user interface.