Opus 5 feels like a downgrade from Opus 4.8 overall. It, along with Fable, really has a problem following instructions and staying in scope, and their prose keeps growing, both in explaining what it did and in writing multiline code comments (some comments read like a changelog, e.g. `// sky is blue (changed from red on 2026-01-01 per TCK-234 by @Foo)`).

Every time I ask it to do something, it does 80% of the job, goes off on "side quests" beyond the scope, and then leaves something out of the core ask (and when you tell it to finish, it does the same thing again).

The only advantage of Opus 5 over 4.8 is the better cutoff date for working with 3rd-party tools, though both do a very bad job of "this tool is constantly updated, I should look for the latest version first".