Your agent leaderboard is ranking scaffolds, reasoning budgets and denominators
Three variables outside the weights now move scores more than the model gaps you're choosing between, and each one is cheap to control.
The harness result alone would be a curiosity. It has company. Three separate measurements show one model name delivering three different systems, and each effect is large enough to flip a model-selection decision.
Variable 1: the scaffold is trainable, not just noisy
The same Hugging Face work shows the harness can be trained against. AINews reports that multi-harness RL on LFM2.5-2.6B, run across four harnesses, moved first-attempt solves from 42% to 54%. SFT on 3,189 rollouts plateaued at 47.5%. The result holds up because a capture proxy records exact token IDs and logprobs rather than re-tokenized text. Retokenization drift would quietly corrupt the on-policy importance ratios. This is one task family and one seed. Read it as a direction, not an effect size.
Variable 2: the reasoning budget actually delivered
TLDR Data reports an analysis of 43,261 Fable 5 calls over six weeks. Delivered reasoning budget varied sharply under a single model name, and many calls showed zero thinking. The analysis has one large confound. It does not control for prompt difficulty, and adaptive-reasoning models are supposed to think less on easy prompts. It also never links budget to correctness. A replay study separates the two explanations. Run a fixed prompt set repeatedly across peak and off-peak windows, then split budget variance into a between-prompt part (adaptive, fine) and a within-prompt part (provider-side, a problem). If within-prompt variance is large and correctness tracks it, the offline eval overstates production quality.
Variable 3: the denominator
Turing Post works through the cost math for Reflection's Beam: cost per solved task = cost per attempt ÷ success rate. On DeepSWE-like work, Beam has to be at least 74.2/44.4 = 1.67x cheaper per attempt, end to end, just to match DeepSeek V4.1 Flash. On codebase QnA against Kimi K3, the bar is 1.97x. Those are floors, since real failures are correlated. Reflection's claimed 3–4x efficiency over GLM 5.2 leaves out prefill, and prefill dominates agent loops that re-read repo context every turn.
Import AI's SciUniverse lab-automation data re-ranks the same way. Claude Fable 5.1 passes 45.3% of tasks at $40.61 per task, about $89.65 per success. GPT-5 Astra passes 32.5% at $52.37, about $161.14 per success. The per-success figures assume tasks can be retried independently. They do not hold for irreversible actions.
| Variable | The evidence | Control |
|---|---|---|
| Harness | Same weights scored 62% vs 33% | Model × harness matrix; production harness is the deciding arm |
| Reasoning budget | Many of 43,261 calls did zero thinking | Log reasoning tokens per call; report evals at the delivered budget |
| Denominator | Beam needs ≥1.67x cheaper attempts to break even | Rank on $/solve, including retries and human-correction time |
Size the test before running it
Turing Post's power math is the part worth copying. SWE-bench Verified has ~500 tasks, and at ~80% accuracy the standard error of an unpaired difference is about 2.5 points. Beam's 2–3 point deficit there is not detectable at all. A paired McNemar test on 200–300 in-house tasks resolves the ~10-point gaps seen on Terminal-Bench 2.1. Resolving 2–3 point gaps takes 1,000+ paired tasks.
A model ranking that doesn't fix the harness, log the delivered reasoning budget and divide by success rate is really a ranking of your test setup.
What to do
Build a model × harness eval matrix this sprint: 2–3 candidate models × 3 harnesses (Mini-SWE-Agent as neutral baseline, your production harness, one commercial-style harness) × ≥3 seeds on 200–300 paired internal tasks. Fit a two-way model to separate model, harness and interaction variance.
Add reasoning-token count as a logged field on every production LLM call. Then run a replay study this sprint: 200–500 fixed prompts × ≥5 replays across peak and off-peak, splitting within-prompt from between-prompt budget variance.
Pre-register the Beam head-to-head now (Beam vs DeepSeek V4.1 Flash vs Kimi K3, ≥300 private repo tasks in one harness, McNemar on pass@1 plus $/solve and p95 latency) and run it the week weights and the tech report ship later in October.