It's definitely possible for AI to do a large fraction of your coding, and for it to contribute significantly to "improving itself". As an example, aider currently writes about 70% of the new code in each of its releases.
I automatically track and share this stat as graph [0] with aider's release notes.
Before Sonnet, most releases were less than 20% AI generated code. With Sonnet, that jumped to >50%. For the last few months, about 70% of the new code in each release is written by aider. The record is 82%.
Folks often ask which models I use to code aider, so I automatically publish those stats too [1]. I've been shifting more and more of my coding from Sonnet to DeepSeek V3 in recent weeks. I've been experimenting with R1, but the recent API outages have made that difficult.
[0] https://aider.chat/HISTORY.html
[1] https://aider.chat/docs/faq.html#what-llms-do-you-use-to-bui...