In this meta-analysis of 15 studies, seven published and eight unpublished, we found that taking more steps per day was associated with progressively lower mortality risk, with the risk plateauing for older adults (aged ≥60 years) at approximately 6000–8000 steps per day and for younger adults (aged <60 years) at approximately 8000–10 000 steps per day. We found inconsistent evidence that step intensity had an association with mortality beyond total volume of steps.
Here’s a quote from the actual study. Emphasis added.
https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(21)00302-9/fulltext
In this meta-analysis of 15 studies, seven published and eight unpublished, we found that taking more steps per day was associated with progressively lower mortality risk, with the risk plateauing for older adults (aged ≥60 years) at approximately 6000–8000 steps per day and for younger adults (aged <60 years) at approximately 8000–10 000 steps per day. We found inconsistent evidence that step intensity had an association with mortality beyond total volume of steps.
So… it is 10 000.