UDIM and UVTILE in the Texture UV Editor
General
The UV mapping extension UDIM ("U DIMension") and UVTILE have been supported since Cinema 4D 2025.3. Both basically do the same thing (in the following description, for the sake of simplicity, only UDIM is used as the term for the functionality). In general, the use of UDIM is recommended, as it is somewhat easier to read and understand due to its consecutive numbering.
Whereas UV mapping was previously limited to UV coordinates 0-1, any number of UV tiles can now be used, which follow the following naming scheme:

Each tile can be assigned an image file, which must then also have this number or its UV coordinates in its name. Each image file could have an individual resolution.

Please also note the UDIM functionality when opening a file in the Texture UV Editor:

If you move UV elements into negative areas of the UV coordinate system, the corresponding tiles are colored red. Negative areas can be used temporarily, for example, to move a UV island there because it is in the way or similar. Otherwise you should avoid red tiles!
UDIMs therefore have the following advantages:
- They have an almost unlimited amount of texture and UV surface available - the only limits are set by their hardware - which means that high Texel Densities are possible.
- A single material can contain any number of textures.
- Better texture organization: Previously, you had to place all textures on one tile. For example, a character's face can now be placed on one tile and hands, feet and clothing on other tiles.
- Textures of individual tiles can be edited independently of each other without having to readjust a huge overall texture.
Other things to know about the UDIM functionality
- Please note that the UDIM functionality does not work with BodyPaint 3D. Exception: the UV tools. Everything that has to do with painting, projection painting and the like does not work correctly with UDIMs.
- If you do not want to use UDIM, work exclusively on the first tile at the bottom left as before.
Example
In the following scene - all 4 pictures hanging on the wall are a single object with a single material - the texel density is perfect in both cases at a greater camera distance (left). However, if you then move the camera to the bottom left-hand picture (top center), the living room image is insufficient - the picture appears pixelated and blurred.

However, if you now move the UV polygon of the image in question to a new UDIM tile and assign a new, larger and detailed texture, the image will be in focus (bottom center). On the right you can see the UV islands and texture.
Also take a look at these files to see the difference in file path and UV mesh (if necessary, load the associated UDIM textures in the Texture UV Editor to view UV mesh and texture):