ParallACT benchmark: multi-principal agent coordination, Opus at 16% success

EliasEskin · x · 2026-11-04

Most multi-agent benchmarks split one global request into compatible subtasks, but in real large repos 1000+ devs each raise independent, sometimes conflicting requests their agents don't even know about; routing everything to a central agent is a bottleneck and single point of failure. The authors introduce ParallACT: starting from real SWE-Bench Pro tasks (Task A) paired with a separately-motivated Task B touching the same code, each agent sees only its own task. Two task types: complementary (must agree on a shared interface to pass integration tests) and contradictory (incompatible edits to the same code, but a joint solution exists). Frontier models struggle — 16% success for Opus 4.8, even when they can talk.

Related event: UT Austin's ParallACT Benchmark: Parallel Agents' Success Crashes to 16%(9 posts)→

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