I’ve been using Opus 4.8 heavily with Claude Code heavily and I haven’t noticed any problems at all with 5. It seems a bit more proactive (not as much pre-ban Fable though). My claude.md and agent prompts are both 〜20kb, and I use memories/rules/skills as well.

Agent to agent communication does appear to have improved considerably. I run the loops to the full context window and with proper working docs I don’t even notice a difference after compaction.