A Rails 8 upgrade introduced a subtle bug where JSON responses contained duplicate keys due to performance optimizations that bypassed key normalization. The issue occurred when merging string and symbol keys in hashes, which Rails 7 silently handled but Rails 8's fast path no longer normalized. The problem can be prevented
•4m read time• From blog.arkency.com
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First reportsThe suspicious lineWhat changed in Rails 8?The changelog confusionGuarding yourself before the upgradeSort: