The answer? No one knows for sure. But that won’t stop people from speculating!
[T]he increase in troop strength will be about 25,000
The Atlantic (Again):
[E]xpect the commander in chief to approve north of 20,000 additional troops
[A] surge of at least 25,000 new US troops
[E]xpected to send 34,000 more US troops
The Guardian (Again):
[P]oised to announce early next week the deployment of up to 35,000 more troops
[E]xpect him to announce an increase of 20,000 to 40,000 additional troops
[D]eploy an eventual 32,000 to 35,000 U.S. forces
[S]ending about 30,000 additional troops
Basically, no one has any idea.