I regularly get codex to do multi hour tasks with a single prompts I don't think thats a big deal anymore. But you don't want a single agent doing all the work. The root agent needs to delegate the work to sub agents. For example, a sub agent for context gathering, then one for planning, then one (or more) for implementation, then another for review. This way the root agent doesn't use up its context window and it just manages from a bird's eye view. I do have the $200 plan though.