As AMD moves forward with their restructuring of the their CPU lineup, they have been announcing change after change. We've known for a while that they plan to put more of a segregation between their different classes of CPUs, making it clear what ones are intended for entry level, workstation, enthusiast work or so on.
Now, AMD has begun to phase out the single-core variants of the Athlon line, replacing them instead with a handful of new Sempron offerings. The single core 3500+, 3800+ and 4000+ 65nm Athlon units are already no longer able to be ordered through them, and the amount will continue to trickle down as they exhaust their supplies. The new Semprons will be using the new naming scheme, and will include the LE-1300, LE-1250, LE-1200, LE-1100 and LE-1150.
Whether or not having only the Sempron as a single-core offering will be beneficial to them remains to be seen. Intel has done largely the same, with the majority of Core processors being dual-core, though Core Solo still exists. No word on when the new Semprons will be available, and AMD has not yet published a press release concerning their plans.