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 more 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. Code Quality: Claude Wins For complex refactors and multi-file changes, Claude consistently produced better code. It understood architectural patterns, maintained consistency across files, and caught edge cases GPT missed. GPT was faster for boilerplate and simple implementations. If I need a quick utility function, GPT-5.4 is 2x faster. Debugging: Claude Wins (Significantly) When I paste a stack trace and 500 lines of context, Claude finds the bug in one shot about 70% of the time. GPT-5.4 gets