For 2.5 pro exp I've been attaching files into AIStudio in the browser in some cases. In others, I have been using vscode's Gemini Code Assist which I believe recently started using 2.5 Pro. Though at one point I noticed that it was acting noticeably dumber, and over in the corner, sure enough it warned that it had reverted to 2.0 due to heavy traffic.

For the bulk data processing I just used the python API and Jupyter notebooks to build things out, since it was a one-time effort.

Copilot experimental (need VSCode Insiders) has it. I‘ve thought about trying aider —-watch-files though, also works with multiple files.