agent brief/2026-09-29

The Harness Beats The Model

Anthropic's IPO-day Sonnet 5.5 "win" meets effort-level scrutiny, OpenAI quietly halves quotas under a "Sol 6" rebrand, and agents keep proving that reliability lives in the harness — not the model.

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The Harness Beats The Model
λsynopses
  • Harness Over Model Reliability lives in context, tools, retries and verification — an unmanaged agent reportedly lost 78.7% of SWE-Bench tasks to context overflow.
  • Benchmark Blowback Anthropic's Sonnet 5.5 Terminal-Bench "win" over Opus 5.5 compares mismatched effort settings; vendor-reported numbers carry caveats.
  • Quotas & Cost OpenAI's Sol 6 rebrand arrives with halved usage, while cost-per-completed-task diverges from list price.
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