I use LLMs to improve aider, which is >30k lines of python. So not a toy codebase, not greenfield.
I used Gemini 2.5 Pro for the majority of the work on the latest aider release [1]. This is the first release in a very long time which wasn't predominantly written using Sonnet.
The biggest challenge with Gemini right now is the very tight rate limits. Most of my Sonnet usage lately is just when I am waiting for Gemini’s rate limits to cool down.
[0] https://aider.chat/docs/leaderboards/
[1] https://aider.chat/docs/faq.html#what-llms-do-you-use-to-bui...