Users Say Opus Training Shift to XML Tags Explains Leak Behavior

Users observed that Opus models after version 4.8 switched training formats from plain-text Human/Assistant markers to XML tags. One hypothesis suggests this mixed-format training explains why Opus 5 readily leaks system details in 'fakebase' mode.

2026-09-01 ~ 2026-09-01 · 3 related posts

• Observations on Opus model Role Token changes — Ratter · 2026-09-01
• Opus training format shift: From plain text to XML tags — Ratter · 2026-09-01
• Hypothesis on Opus 5 leakiness: Mixed old and new training formats — Ratter · 2026-09-01