Codex (GPT-5.4 mini with medium reasoning) now ships as the default agent in JetBrains AI after offline benchmarking on 353 real tasks across Java, C#, and Python — you can still switch agents anytime.
June 29, 2026
Summary
Eliminates agent selection friction for new users while maintaining choice. The benchmark data (solve rate, cost, latency across ecosystems) is reproducible and published, so you can validate whether this default matches your workflow.
Why it matters
Eliminates agent selection friction for new users while maintaining choice. The benchmark data (solve rate, cost, latency across ecosystems) is reproducible and published, so you can validate whether this default matches your workflow.
Implementation verdict
Replaces the prior Chat-first UX where users manually selected agents. Requires JetBrains AI subscription; no code changes needed. Worth trying now if you use JetBrains IDEs—default is sane and you retain full agent switching. For Java it solves 43.9% of real tasks at $0.13/task; C# at 62.6%; Python at 20.2%.
Sources
Dev Signal
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