I have used over 40B tokens and spent over $800 on DeepSeek API over the past 30 days, mostly on V4.1 Flash.

It's good, and you can do most work with this. For complex software implementation you need to split your runs into various phases, build in verification, and use subagents so that work gets another audit and repair pass from the lead agent. You can do pretty much everything then. Frontier models can do without compelx workflows, that's the difference.