PROC OPTGRAPH can handle any graph whose number of nodes and links are less than or equal to 2,147,483,647 (the maximum that can be represented by a 32-bit integer). This maximum also applies to 64-bit systems. For graphs of two billion nodes (or links), memory limitations also become a limiting factor. For example, see the discussion of memory requirements for the community detection algorithm in the section Memory Requirement
If the data from your problem require a graph with more than two billion nodes (or links), there is typically a heuristic way to break the network into smaller networks based on problem-specific attributes. Then, using DATA steps, you can process each of the smaller networks iteratively through repeated calls to PROC OPTGRAPH. By using DATA steps, you can also often work around memory limitations, because the full graph exists only on the disk and never resides in-memory.