GPT-5.4 vs Claude Opus 4.6 — An Honest Comparison After Using Both for a Month

I've been using GPT-5.4 and Claude Opus 4.6 daily for the past month across real projects. Not benchmarks - actual production code, debugging sessions, and architecture decisions. Here's what I found. Context Window: GPT-5.4 Wins on Paper GPT-5.4's 1M token context sounds incredible. In practice, I rarely needed than 200K. But when I did - feeding it an entire codebase for a migration - GPT handled it without quality degradation. Claude starts losing coherence around 400K in my experience.