The National Institute of Aging's Interventions Testing Program (ITP) is the gold standard for lifespan extension studies in mice. They run large multi-center studies to study the effects of candidate drugs on rodent longevity.
As of 2023, "the ITP has identified nine agents that significantly increase median lifespan — acarbose (Harrison 2014, Strong 2016, Harrison 2019), aspirin (Strong 2008), canagliflozin (Miller 2020), captopril (Strong, 2022), glycine (Miller 2019), nordihydroguaiaretic acid (NDGA) (Strong 2008, Strong 2016), Protandim® (Strong 2016), rapamycin (Harrison 2009, Miller 2011, Wilkinson 2012, Miller 2014) and 17α-estradiol (Harrison 2014, Strong 2016, Harrison 2021)."
The winning compound can be a single drug or a combination of drugs. This question is for male mice only. P-value has to be < 0.01. The impact on maximum lifespan is not taken into account for this question. The question will be resolved based on the official ITP results available on January 1, 2031. This question concerns the drug(s), not the dosage or the age at initiation.
Anyone can add a new answer: please do so if you can instead of voting "Other".
Two new successful ITP interventions in male mice: astaxanthin (+12%, p-value = 0.003) and meclizine (+8%, but p-value = 0.03): https://link.springer.com/article/10.1007/s11357-023-01011-0
Here's a great overview of previous results: https://medium.com/apollo-ventures-insights/the-most-promising-longevity-drugs-to-date-fb7742177527