You are using the "auto-switch back to Sonnet" mode right? Try just selecting Opus without the auto-switch, probably you'll get more Opus and may not run out of it. Anthropic is just being careful because Opus eats compute and they don't want people getting disappointed. But for me it does not run out that quickly. Only when I asked it to work on a 50k+ source code file, which it had to ingest entirely in my case, is when I ran out.