From the source
The fast preset uses numbered citations, while low, medium, and high use source-typed citations.
Perplexity· 28 JulInline citations for research presets
Perplexity's Agent API adds inline citations to its search-backed presets (fast, low, medium, high).
Capability change
From the source
The Agent API's search-backed presets include inline citations: fast cites claims drawn from search results with numbered citations such as [1] , while low , medium , and high now cite claims drawn from tool results or provided source artifacts with source-typed citations such as [web:1] .
docs.perplexity.ai