Instagram quietly shifted weighting toward watch-time-per-viewer rather than completion rate alone. That single change has reshuffled which ad formats get pushed.
Winners and losers
Short, punchy Reels under 15 seconds lost some distribution. Slightly longer, narrative-driven Reels in the 25-40 second range gained it.
What to adjust
If you optimized hard for sub-15-second completion rate, it’s worth testing a longer format before assuming your creative strategy needs an overhaul.