Breaking

GPT-5.5 Takes #2 on Agent Arena, Just Behind Claude Fable 5

June 11, 2026 at 15:35 EDT

Foundation Models
AI Agents
Software Dev & Coding

On the Agent Arena leaderboard run by Arena.ai (formerly LMArena), OpenAI's GPT-5.5 (xHigh) ranked #2 with a net improvement of +10.6%, trailing first-placed Anthropic Claude Fable 5 (High) by a narrow margin. In the ranking around June 11, 2026, GPT-5.5 stood as the highest-placed OpenAI model.

Agent Arena · Agentic Evaluation

GPT-5.5 Surges to #2 on Agent Arena — but Claude Fable 5 Still Leads

OpenAI's GPT-5.5 (xHigh) lands second overall with a net improvement of +10.6%, its best-ever placing. Anthropic's Claude Fable 5 (High) holds first, keeping the two locked in a close agentic race.

GPT-5.5 overall — highest-placed OpenAI model

+10.6%

GPT-5.5 net improvement

300K+

Real tasks · 2M+ tool calls · 40M lines of code

Per-signal breakdown — who leads each metric

+29.4%

Praise vs Complaint

GPT-5.5 leads

+14.1%

Bash Recovery

GPT-5.5 leads

+17.6%

+5.4%

Confirmed Success

Claude Fable 5 leads

+5.4%

+1.9%

Steerability

Claude Fable 5 leads

GPT-5.5 (xHigh) Claude Fable 5 (High)

Where each shines

Claude Fable 5 — reliable in complex tool workflows, strong frontend building
GPT-5.5 — high praise ratio, resilient recovery from bash errors

Cautions raised

Long-running tasks can collapse as errors compound
Leaderboards capture only what is easily measurable

On a related metric

Claude Fable 5 also tops the Artificial Analysis Intelligence Index at 64.9, leading GPT-5.5 by about five points. The agentic-performance contest between the two looks set to intensify.

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