EDIT: UDIM is officially in master, this thread remains relevant as there are always improvements that can be made.
A couple of things.
----This doesn’t appear to be specific to Cycles, which makes me wonder if Eevee will support it too.
----There is nothing usable here yet, so don’t build the branch and then wonder why nothing works.
UDIM file loading.
https://lists.blender.org/pipermail/bf-blender-cvs/2018-June/109954.html
The start of the ability for Blender to draw the UDIM grid.
https://lists.blender.org/pipermail/bf-blender-cvs/2018-June/109955.html
+10
will this also allow in the PTEX thing ?
happy cl
what am i looking at exactly
in short, its a technology from ~2002, originally created by Weta Digital.
It allows the spreading of UV-Islands to multiple tiles which starts at 1001 and can go up to 9999.
this allows to use multiple “smaller textures” while having more overall resolution, instead of having to use one giant texture where you have to cram everything in.
Textures which are assigned to those numbers can be automatically loaded into the program.
This method is more commonly used for Film production but for example Unity seems to be able to understand it too…
UDIM and Ptex are two completely different technologies (UDIM still makes use of UVmaps and editable image files).
Ptex meanwhile is more exotic due to how it attempts to eliminate the concept of UVmaps altogether (at the cost of the resulting files not being editable), but last I heard it does not work well with threads (a big deal if you want fast rendering).
wow that sound great, loading a 4k texture to your model is really a pain
A lot of progress today. UDIM’s are now visible in the render engines and the viewport and now we have the start of painting support.
Lukas today added code related to the drawing of UDIM tiles, one now can also add and remove tiles as needed.
https://lists.blender.org/pipermail/bf-blender-cvs/2018-June/110147.html
This is so incredibly good and is the biggest features of 2.8 that I’ve been looking forward to, honestly it was one of the main features of cycles preventing it from competing against other industry standard renderers. Now we just need better displacement with UV smoothing support and it’ll be perfect.
Substance painter doesn’t allow painting on a single character with UDIM, so I hope Blender will be able to do it.
What do you mean with “on a single character”? Painting across tiles?
Yes 
Painter is not capable to do it and it’s a paint to paint a big character.
Ah, okay - in the first iteration (will be pushed in ~10min) it’ll also be single-tile (it autodetects which tile the start of the stroke was in), but I’ll look into cross-tile painting next.
Great thank you
Awesome if you can make it work!
3D painting now works.
https://lists.blender.org/pipermail/bf-blender-cvs/2018-June/110208.html
Tiles can be of different sizes
https://lists.blender.org/pipermail/bf-blender-cvs/2018-June/110216.html
Live redraw for secondary tiles
https://lists.blender.org/pipermail/bf-blender-cvs/2018-June/110217.html
The scale of the brush can now take the different tile sizes into account.
https://lists.blender.org/pipermail/bf-blender-cvs/2018-June/110224.html
Recent commits indicate that painting on the UDIM tiles are more or less fully functional now, visual polish like tile highlighting, and one or two optimizations (such as Cycles not loading tiles that are empty).
Did someone try this branch ? In the N panel of the UV/image editor, there is a button “Add tile” but it is disabled, how can I have it enabled ?