I found another example of a trial stopped for early efficacy.  CREDENCE - initially thought to last for 5 years, stopped after 2.5, 4400 patients, and I believe our own Dr. KKZ was involved with this trial.

The CREDENCE trial was initially predicted to have a total study duration of 5 years. However, the trial was stopped early at around 2.5 years after an interim analysis showed clear benefit for the primary outcome. The group receiving canagliflozin showed a significantly lower event rate for the primary composite outcome compared to the placebo group, with a hazard ratio of 0.70 (95% CI 0.59-0.82; p = 0.00001). The beneficial effect of canagliflozin also held true for each individual renal components of the primary outcome. The CREDENCE trial also demonstrated benefit in the composite outcome for cardiovascular death, myocardial infarction, or stroke (HR 0.80 [CI 0.67-0.95]; p=0.01), as well as for heart failure hospitalization (HR 0.61 [95% CI] 0.47-90.8; p < 0.001), in accordance with the results of three major trials preceding it. Interestingly, these benefits were observed despite modest group differences in blood glucose and blood pressure, suggesting that the mechanism of SGLT2 inhibitor benefit may actually be independent of blood glucose and instead rely on decreases in glomerular hyperfiltration. The analysis found no significant differences in adverse effects between canagliflozin and placebo, including the increased risk for amputation observed in the CANVAS trial.8

https://www.acc.org/latest-in-cardiology/articles/2020/04/22/08/10/canagliflozin-and-renal-outcomes-in-type-2-diabetes-and-nephropathy-credence-trial