Researchers developed plasma p‑tau217‑based clock models that predict the age of symptomatic Alzheimer’s onset within a three‑ to four‑year margin of error by correlating blood p‑tau217 dynamics with amyloid and tau accumulation patterns. The work analyzed over 600 older adults across two cohorts and compared plasma measures to PET imaging and clinical trajectories. The models, published in Nature Medicine, use p‑tau217 as a proxy for neuropathology accumulation and can estimate the interval between biomarker elevation and symptom emergence—information that could refine trial enrollment and timing for preventive therapies. Investigators cautioned that while the clocks provide population‑level timing signals, uncertainty at the individual level remains substantial; they recommended careful validation before clinical deployment. Next steps: external validation across diverse populations, integration into trial inclusion criteria, and assessment of clinical utility for counseling and therapeutic timing.