The 2GB LOB limit only applies to *persistent storage*; variables have no limit.

SQL Server **starts** with an pure in-memory implementation.

It **changes** to a *tempdb*-based backup scheme if the size of the LOB data *grows beyond* 512KB (524,288 bytes).

The backup scheme stores LOB data in a tree of internal *tempdb* LOB pages.

These *tempdb* pages are cached in the buffer pool as usual, but may be flushed to disk by the lazy writer as needed.

There are extra overheads in using the *tempdb*-backed scheme even if all pages remain in memory.

When the variable goes out of scope, the pages are synchronously deallocated. This can take time for very large LOBs.

```
DECLARE 
    -- 512KB: In-memory
    @V1 varchar(max) = REPLICATE(CONVERT(varchar(max), 'X'), 524288),
    -- 512KB + 1: Buffered, tempdb-backed
    @V2 varchar(max) = REPLICATE(CONVERT(varchar(max), 'X'), 524289);
```

The limit is in bytes, so the number of characters stored depends on the encoding.