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Coding Agent Index v2.1: scores fell 5 points, 4 configs tie at 58, and cost per task spans 30x
On November 14 Artificial Analysis shipped version 2.1 of its Coding Agent Index, the leaderboard that scores a coding agent as one unit of harness plus model plus effort setting. The short version: nearly everyone lost points, the lead is a four-way tie at 58, and the cost to run one task at the top of the board spans roughly 30x. When the index reset in October I wrote about what the v2.0 reset measures. The v2.1 change is narrower but sharper, and the cost column is the part worth your time if you pick models for a coding agent. What v2.1 changed The index is an equal-weight average of three benchmarks, 322 tasks total, three attempts per task: Component Tasks What it measures How it scores FrontierCode-AA 2.0 132 changes to real open-source repositories maintainer-merge rubric, 0 or 70-100% Terminal-Bench 4.1 66 multi-step terminal work test suite, pass/fail SWE-Atlas-QnA-AA 124 repository question answering binary pass/fail FrontierCode-AA 2.0 is Artificial Analysis' implementation of Cognition's FrontierCode 2.0, released October 27. An attempt that fails any blocking check scores zero. An attempt that passes them all scores between 70% and 100% depending on non-blocking checks. A trajectory scanner zeroes any attempt that went looking for the upstream solution or its merge commit. Terminal-Bench 4.1 keeps 4.0's 66 tasks and environments and replaces the verifiers. Code that runs during grading now runs as an untrusted user in a separate process, and verifiers that rejected valid solutions were corrected. That is reward-hacking hardening, not new tasks. The third component and the weighting did not change. The largest component got harder, and that moved the whole board. The full methodology page is worth a read. All 23 dual-measured configs lost points on the new FrontierCode Per the v2.1 announcement, index scores came down about 5 points on average, driven by the FrontierCode swap. AlphaSignal's read of the underlying data is more specific: all 23 configurations evaluated on both versions scored lower on the new FrontierCode, and the mean FrontierCode score fell 16 points, from 45% to 29%. That is not the models getting worse. FrontierCode 2.0 pulls from 55% more repositories, carries 43% more blocking criteria per task, and its reference solutions modify 67% more files and 89% more lines in codebases that are 25% larger. The share of thoroughness criteria roughly tripled. Thoroughness criteria catch the patch that fixes the reported case and misses the sibling code path, and Cognition reports thoroughness produced the highest blocker failure rate at every reasoning level they analyzed. One configuration barely moved: Codex with GPT-6.1 Terra at max effort stayed within a point of its previous index score. Everyone else ate the reset. This is the second consecutive version change that lowered scores across the board. That is the design. A suite that refreshes before vendors tune against it keeps some discriminating power. A score you saw quoted last month is a different exam. The lead at 58 is two models in four configurations The top score belongs to four configurations, not one product: Claude Code with Fable 5.2 at high effort, Claude Code with Fable 5.2 at xhigh, Claude Code with Opus 5.5 at max, and Devin Fusion CLI with Opus 5.5 Max paired with GPT-6 Luna High. Two details matter more than the rank. First, Fable 5.2 at max scores 56, below its own high-effort result, because more of its attempts hit task time limits. Effort is not a simple dial where more is better. Second, Gemini 4 Carbon at high effort scores 55 in Antigravity CLI. The index deliberately scores the harness and the model together, which is why I trust it more than raw model benchmarks for agent work. We have seen this before from the other side: Hugging Face measured the same model scoring 33% or 62% depending on the harness. The 30x cost spread is the actionable column v2.1 also changed how cost is computed. Artificial Analysis aligned it ...
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