Her aides still don't expect Sen. Clinton to formally concede and endorse Sen. Barack Obama tonight, but if, as seems likely, Obama ends up with more than 2118 delegates by the time she speaks, Sen. Clinton is certain to publicly acknowledge that Obama has crossed the threshold. That means, in essence, that the Democratic primary campaign is over.
The AP puts this with more certainty than I'm able to, at this point:
"Officials say Clinton will acknowledge Tuesday night Obama has the delegates for the nomination."
The former first lady will stop short of formally suspending or ending her race in her speech in New York City. She will pledge to continue to speak out on issues like health care. But for all intents and purposes, the two senior officials said, the campaign is over. Most campaign staff will be let go and will be paid through June 15, said the officials who spoke on condition of anonymity because they were not authorized to divulge her plans.