Hallucination Fan-Out

Properties

family: propagation
severity: systemic
triggerError: A single agent emits a hallucinated or unsupported claim into a shared artifact.
mechanism: Downstream agents consume the claim as ground truth and build on it, so one local error becomes shared team context that no single agent re-checks.
blastRadius: Every agent that reads the poisoned artifact inherits the error; the affected set grows with the fan-out degree of the topology. Depth is a different axis: in sequential refinement chains, hallucination can attenuate rather than amplify (normalized hallucination score fell from 0.422 at the first agent to 0.272 at the final agent across 3-agent chains, a 0.644 amplification factor), at the cost of small consistent losses in factual consistency and response quality (arXiv:2606.07937).
mast: [Cat 2][Cat 3]
detection: Divergence between a propagated claim and its cited source; an independent verifier that re-derives the fact disagrees with the consumed value.
mitigation: Independent verification before an artifact is shared (build-verify-reflect); provenance tags so downstream agents can discount unsourced claims.
source: Why Do Multi-Agent LLM Systems Fail? (MAST, arXiv:2503.13657)

family: propagation
severity: systemic
triggerError: A single agent emits a hallucinated or unsupported claim into a shared artifact.
mechanism: Downstream agents consume the claim as ground truth and build on it, so one local error becomes shared team context that no single agent re-checks.
blastRadius: Every agent that reads the poisoned artifact inherits the error; the affected set grows with the fan-out degree of the topology. Depth is a different axis: in sequential refinement chains, hallucination can attenuate rather than amplify (normalized hallucination score fell from 0.422 at the first agent to 0.272 at the final agent across 3-agent chains, a 0.644 amplification factor), at the cost of small consistent losses in factual consistency and response quality (arXiv:2606.07937).
mast: [Cat 2][Cat 3]
detection: Divergence between a propagated claim and its cited source; an independent verifier that re-derives the fact disagrees with the consumed value.
mitigation: Independent verification before an artifact is shared (build-verify-reflect); provenance tags so downstream agents can discount unsourced claims.
source: Why Do Multi-Agent LLM Systems Fail? (MAST, arXiv:2503.13657)