Artificial Analysis Coding Agent Index v2.0: Claude Opus 5.5 Leads
The v2.0 changes make rankings harder to game: private test sets, anti-solution scanning and multi-vote LLM judging push mean scores down 1.7 points across 21 shared configurations. Teams choosing a coding agent should note that Opus 5.5's edge is concentrated on FrontierCode (56.0% versus 52.6% for DeepSeek V4.1 Flash), while 15 of 24 configurations cluster between 43% and 49%, so harness choice can matter as much as model choice.
Artificial Analysis launched v2.0 of its Coding Agent Index on X, evaluating model-plus-harness pairs across 290 tasks covering software engineering, terminal use and repository Q&A. FrontierCode v1.1 from Cognition replaces DeepSWE, with 100 private tasks on real open-source repositories graded on whether a maintainer would merge the change. SWE-Atlas-QnA grading was revised into SWE-Atlas-QnA-AA, using GPT-6 Luna (xhigh) as the judge with five votes per criterion. Claude Code with Claude Opus 5.5 (max) leads at 61.7, ahead of Claude Sonnet 5.5 at 59.3 and Muse Code with Muse Wonder Full at 58.9.
Announcing Artificial Analysis Coding Agent Index v2.0: FrontierCode v1.1 from Cognition replaces DeepSWE, SWE-Atlas-QnA grading is revised, and Claude Opus 5.5 in Claude Code leads at 61.7
Today we are launching v2.0 of the Coding Agent Index. The Index evaluates models together with their agent harnesses, now across 290 tasks covering software engineering, terminal use, and repository Q&A, with the three benchmarks weighted equally.
Changelog (Index v1.5 → Index v2.0):
→ FrontierCode v1.1 replaces DeepSWE v1.1. FrontierCode is a benchmark from @cognition with a private test set: 100 software engineering tasks on real open-source repositories, graded on whether a maintainer would merge the change. An attempt that fails a blocking check scores zero, and one that passes them all scores between 70% and 100% depending on the non-blocking checks it meets. We also scan each trajectory with a modified version of Cognition's rule-based scanner, and any attempt flagged for accessing solution material scores zero.
→ Revised SWE-Atlas-QnA grading, now SWE-Atlas-QnA-AA. Scale AI's 124 repository Q&A tasks are unchanged. We reworded 127 of the 1,306 rubric criteria for more consistent verdicts and moved to GPT-6 Luna (xhigh) as the judge, with five votes per criterion. The dataset and judge configuration are published on Hugging Face.
Key results:
➤ Claude Opus 5.5 leads the Index: Claude Code with Claude Opus 5.5 (max) scores 61.7, followed by Claude Code with Claude Sonnet 5.5 (max) at 59.3, Muse Code with Muse Wonder Full (max) at 58.9 and Claude Code with Claude Fable 5.1 (max with fallback) at 57.6.
➤ FrontierCode v1.1 is where Opus 5.5 pulls ahead: Opus 5.5 scores 56.0% on FrontierCode, ahead of Codex with DeepSeek V4.1 Flash (max) at 52.6%, Codex with GPT-6.1 Sol (max) at 49.4% and Codex with GPT-6 Astra (max) at 49.3%. Below the top, FrontierCode scores are tightly packed: 15 of the 24 configurations on the Index score between 43% and 49%.
➤ SWE-Atlas-QnA-AA grading is stricter and more consistent: across the 21 configurations evaluated on both Index versions, the mean score falls 1.7 points, from 58.8% to 57.1%, with 14 of 21 moving down. Individual configurations move by up to 7 points: Muse Code with Muse Spark Open (xhigh) falls 7.0, Kimi K3 in Kimi Code CLI and Codex with GPT-6 Luna (max) 6.2, and Muse Code with Muse Wonder (max) 5.6, while Codex with GPT-6.1 Sol (max) gains 2.1.
➤ Four configurations sit on the cost frontier: Codex with DeepSeek V4.1 Flash (max) scores 47.3 at $0.39 per task, Codex with GPT-6.1 Sol (max) 54.1 at $1.50, Codex with GPT-6 Astra (max) 54.7 at $7.04 and Claude Code with Claude Opus 5.5 (max) 61.7 at $11.42. Costs are pay-per-token API costs, not subscription prices.
We will keep updating the Coding Agent Index incrementally, with more evaluations and agents to come.
