agent brief/2026-09-28

The Harness Is the Product

Across sources, practitioners converge on one claim: agent reliability is engineered in the runtime, not the model — and the benchmarks keep proving it.

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The Harness Is the Product
λsynopses
  • Reliability Moves Outward LangGraph tops framework comparisons for observability and HITL, while tool-calling, tracing and guardrail guidance all place enforcement in the runtime.
  • Benchmarks Crack A vLLM stress test reportedly drops Llama-3.1-70B tool-selection accuracy from 95% to 20% as catalogs grow; sub-1B routers are the proposed fix.
  • Quants Hide Damage One user's identical 4-bit AWQ runs on DeepSWE diverged by ~7 points and solved different task sets.
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