Artificial Analysis Coding Agent Index v2.1 Moves to FrontierCode 2.0 and Terminal-Bench 4.1: Claude Fable 5.2 and Claude Opus 5.5 Tie for First at 58, Scores Drop 5 Points on Average
On November 14 Artificial Analysis released Coding Agent Index v2.1, swapping FrontierCode 1.1 for its implementation of Cognition's FrontierCode 2.0 (132 real-world tasks graded on whether a maintainer would merge the change), upgrading Terminal-Bench from 4.0 to 4.1 and keeping SWE-Atlas-QnA-AA. Claude Fable 5.2 (xhigh and high, in Claude Code) and Claude Opus 5.5 (max) share the lead at 58. Because FrontierCode 2.0 is harder, scores fall 5 points on average; only Codex with GPT-6.1 Terra (max) held within 1 point of its prior score.

- •v2.1 is made of FrontierCode-AA 2.0 (132 real-world coding tasks graded on whether a maintainer would merge the change), Terminal-Bench 4.1 (the same 66 tasks with updated verifiers for reliability and resistance to reward hacking) and SWE-Atlas-QnA-AA
- •Tied for first at 58: Claude Code with Claude Fable 5.2 (58 at both xhigh and high), Claude Code with Claude Opus 5.5 (max), and Devin Fusion CLI (Opus 5.5 max + GPT-6 Luna High); next come Claude Sonnet 5.5 (max) at 56 and Antigravity CLI with Gemini 4 Carbon (high) at 55
- •All 23 configurations tested on both versions score lower on FrontierCode-AA 2.0 than on v1.1, with the mean falling from 45% to 29%; Claude Code with Fable 5.2 leads at 49%. On Terminal-Bench 4.1 every score moves less than 3 points, and Kimi Code CLI with Kimi K3.1 Pro leads at 68%
- •Cost varies about 30x: among configurations scoring 48+, Codex with GPT-6.1 Sol (max, 52) costs $1.51 per task and Claude Code with Fable 5.2 (max, 56) costs $44.22; Fable 5.2 costs $2.89, $7.51 and $15.47 at medium, high and xhigh
- •Claude Code and Devin Fusion CLI fall back to another model after a safety refusal: a fallback model completed about 9% of attempts for Devin Fusion CLI and Opus 5.5 (max), 6% for Fable 5.2 (xhigh) and 5% for Sonnet 5.5













