For starters, there's a C++ application written with MFC and an absolute ton of inline assembly and threading (yes, in a 1990's C++ application). I'm porting it to MacOS/Linux currently.

Opus 4.6+ is able to make slow progress, but it takes several revisions per workstream. It requires constant supervision as it often creates convoluted solutions that expand the code in bloated ways. It works, but still requires my constant input.

Fable was able to almost one shot most of the big migrations with very few bugs, and was able to fix those bugs with 1 review pass. I almost didn't believe it. I was able to put it on a task (with dangerous permissions) and come back hours later to see it done, working, and clean.

I tried DeepSeek v4 and it wasn't able to make any meaningful progress at all. It kept creating dangling pointers and had trouble understanding the inline assempbly needed to be replaced if we were to compile for 64 bit. It kept getting stuck and looping on the same problem, without making progress.

What I do use DeepSeek for is lots of my automations on my websites. I find DeepSeek is fantastically cheap and fast and effective as summarization, collation, generating reports, finding and reporting issues from logs, etc. But I haven't found a way to get it to effectively port 90's C++ code to modern, cross-platform standards. But I want to be clear- I really like DeepSeek and use it wherever I can.. I mean.. it's so affordable!