# What's the difference between a proven cause and a lead in an RCA report?

A proven cause has a located change, a diff, a prompt edit, a retrieval-code change, lining up with the trace evidence and is marked `high` confidence and carded on the case page; a lead is unconfirmed to that bar, still backed by trace evidence but with no located change, marked `medium` or `low`, and shown only when the report has no proven cause for that finding.

Every RCA report now writes the same shape, on a metric-movement case or a frustration or groundedness one: a one-sentence summary, a verdict, and causes carrying a title, what changed, how that caused the shift, and what to do next, each cited to the traces or sessions it draws from, the same standard [any regression investigation is expected to meet](/answers/cause-attribution/what-evidence-a-regression-investigation-needs). That's new as of a September 2026 update; reports before it wrote a flat, unranked list with no confidence tier at all.

A report with no proven cause and no surviving lead still reads `no_cause_found`, same as before. Leads are new visibility into what the investigation considered and couldn't confirm, not a lowered bar for what counts as a named cause.

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Sources:
- Tessary commit bbac959, "One readable cause shape for every RCA": https://github.com/tessaryai/tessary/commit/bbac959b4a524cb2acb2b40e7f7ec41087aa4583 (fetched 2026-09-30)

Source: https://tessary.ai/answers/tessary-rca/whats-the-difference-between-a-proven-cause-and-a-lead-in-an-rca-report
More on Tessary RCA: https://tessary.ai/answers/tessary-rca
From Tessary, agent reliability for AI agents in production: https://tessary.ai