There's been a lot of discussion recently around how Claude Code updates affect behavior, predictability, and token usage. When Claude Code updates, it's not just the model that changes - the CLI harness, system prompts, tool-calling behavior, and context management all evolve too. Newer is often better. But not always for every workflow. In my own setup, I noticed that some skills, agents, and project workflows I'd built behaved differently after recent updates. Not necessarily worse, but differently enough that predictability started to matter. For AI-assisted development, that matters. The problem Sometimes you want the latest model. Sometimes you want the setup your workflow was built around. There's no built-in way to run an older Claude Code version side-by-side with the latest one. If you pin the model with --model , you still get the latest harness — and harness changes can affect behavior just as much as model changes.…