Segmentation
Segments are an opaque batch job: simple filters can take 15 minutes to populate, complex ones much longer, and behaviour at million-profile scale is inconsistent.
What people actually say
✕Klaviyo's own product team acknowledged segmentation speed problems and shipped an upgrade specifically targeted at extremely complex segments and accounts with millions of profiles.
Source: Klaviyo Community, segmentation upgrades ↗✕Customers report 20-25 minute delays between a profile entering a segment and the first flow email firing, with no built-in way to inspect or trace why a profile failed to enter.
Source: Klaviyo Community, slow flow triggers ↗✕Exporting even modest segments can take several minutes and large exports routinely exceed 20 minutes, making ad-hoc list pulls and audit checks painful.
Source: Klaviyo Community, slow performance ↗
Segments are SQL views against your Postgres or DuckDB profile store, evaluated in milliseconds, not minutes. The same query that powers a flow trigger powers a campaign send and a Metabase dashboard, so a marketer can validate counts before pulling the trigger. Exports are a streaming CSV from the database, not a job queue you wait on.