V2
It turns out you can still outpaint with Flux.2 dev without using LanPaint. It just needs the right prompts and more steps.
V1
This is an experimental workflow for outpaint in Flux.2 dev (not Klein) using LanPaint custom node.
Please be informed LanPaint is extremely slow. Even with Turbo lora, a minimum of 40 steps (i.e. 8 x 5) are required.
The result is hit-and-miss. Sometimes, the output image before stitch is better than the one after stitch.