I wouldn't even considering hiring a junior engineer at this point. The ROI was already barely breakeven for any but the top of the top junior engineers as they are likely to move on before they are meaningfully contributing.
With AI in the mix the ROI for Junior Engineers is strongly negative for 2 reasons:
1. (obvious) I can just have Claude Code do the work a junior engineer would have done with faster turnaround and generally better results.
2. (less obvious) Junior engineers are going to just turn around and use Claude Code, so now I'm talking to an AI and playing the telephone game, and the Junior engineer isn't going to learn much if anything in the process.