I feel like this article isn't saying much. Even with tools disabled, Claude Code still has a crap load of commands and other things that Claude (the model) should know the availability of since it's optimized for them. All of that has to be disabled if this is to be a real harness comparison. And of course the system prompt can be completely replaced, making it a no-brainer to use a more minimal prompt similar to OpenCode. And beyond that nothing else really matters because the rest (cache behavior, etc) lies with the provider's platform, not the harness.