18:22
2026-09-29
stackness.dev
large-language-models
Opus 5.5 in a harness: empty thinking blocks, time budgets and agents that stop early
Anthropic's Opus 5.5 prompting guide documents two harness-level failure modes for the model released 22 September 2026: progress-update thinking blocks return empty text at the default display: "omitβ¦