Which GUI text editors can reliably handle files over 100 MB?

Sublime Text has been used successfully with files around 2 GB, so it may be worth trying if the smaller editors struggle. CudaText is another lightweight GUI editor to consider.

For very large files, you could also look at editors designed around large-file handling, such as UltraEdit or a large-file editor from Liquid Technologies. Emacs has VLF support as well, and tools such as vis may be useful on Unix-like systems. If the file is generated data, logs, or something that needs repeated processing, scripting or command-line tools will usually be more practical than manually editing it.

The best choice depends on the task. For simply reading a huge file, a pager such as less is usually much faster and uses fewer resources. Editing is more difficult because inserting or deleting text may require rewriting a large portion—or all—of the file. Vim/GVim can still work well for files in the hundreds of megabytes, but it loads the file into memory and typically rewrites the whole file when saving.

Kate is a solid free, open-source option and generally handles large files well. Gedit, KWrite, Vim, and GVim can also open files around this size on a reasonably equipped system. If you prefer Vim without the usual modal behavior, launch GVim with its modeless option.