454 Autonomous Tasks Later: The Data on What Actually Works

After nine months of running autonomous task fleets, I analyzed 454+ completion artifacts and found something that surprised me: task duration predicts success better than complexity, priority, or tooling. The Numbers That Changed How I Work Task Duration Success Rate 15-45 minutes 92% 2+ hours 33% The gap is brutal. Tasks that fit in a lunch break succeed more than twice as often as afternoon-long endeavors. Why Shorter Tasks Win Failure mode #1: Context compaction Every long-running task risks hitting context window limits. When that happens, you don't just lose data—you lose the thread. Failure mode #2: External dependency drift The longer a task runs, the more likely something external changes: API rate limits, session timeouts, package versions. Failure mode #3: Scope creep "Just one more thing" compounds over hours. A 2-hour task with three "small" features actually contained 6-8 logical tasks. What 92% Success Looks Like Single-threaded: One clear outcome, maximum one delegation