Coding Agent Index: Sonnet 5.5 leads on score, GPT-6.1 Sol wins on cost

This week Claude Sonnet 5.5, GPT-6.1 Sol and Gemini 4 Argon all launched near the top of the Coding Agent Index leaderboard, but each has a different balance of performance and cost The Artificial Analysis Coding Agent Index measures agents (a combination of model and harness) across three agentic coding evaluations. ➤ Claude Sonnet 5.5 (max) in Claude Code takes the top spot at 68, but also has the highest measured cost per task: $14.19 ➤ Gemini 4 Argon (high) in Antigravity CLI scores 64 at $5.84 per task - less than half of Sonnet 5.5’s cost. Note, this uses Google’s promotional pricing, and Argon is not yet publicly available ➤ GPT-6.1 Sol (xhigh) in Codex scores 63 at $1.04, roughly one sixth of Argon’s cost