Every multi-agent architecture makes a bet: that the coordination overhead is cheaper than the context bloat of a monolithic session. Nobody has published the actual cost.
Mohammad Fauzel Sadeghizad ran 45 controlled experiments across 20 programming tasks to measure the fork tax: the performance penalty you pay when you split an agent workflow into subsessions instead of running it inline. The methodology includes pre-registered rubrics, deterministic fixtures, and an independent adversarial verification audit.
The findings are unambiguous. Sometimes the orchestration wins. Sometimes it loses badly. The difference comes down to plumbing, not theory.
The Subsession Invariant
The architectural claim behind subsessions is simple: a coordinator agent spawns child sessions, each child returns a structured report, and the coordinator's context grows by O(report) instead of O(child transcript).
