Diane Sawyer will be stepping down as anchor of ABC’s “World News” following a five-year stint and will be replaced by the network’s own David Muir, the network announced today. ABC executives say that Sawyer will stay on at the network to “lead new programming tackling big issues and extraordinary interviews,” according to an ABC News release. The switchover will occur on Sept. 2.

Muir, 40, will take over “World News” but all the perks of the lead anchor position at the network won’t fall to him. As part of the same personnel move, ABC News has announced that George Stephanopoulos will be the top anchor in breaking-news scenarios, not to mention coveted election-night specials. That’s a logical move, considering that Stephanopoulos currently hosts ABC’s Sunday morning show “This Week.”

Exactly what role Muir will play in election night coverage remains to be seen, according to a network source, though he’ll certainly have a role. Note that the press release announcing the changes lists Stephanopoulos as chief anchor of ABC News and Muir as anchor and managing editor of “World News.”

The move from the 68-year-old Sawyer to Muir reflects an attempt by ABC News to make further gains in what TV nerds call the “demo,” the audience of people aged between 25 and 54 whose viewing decisions drive advertising dollars. ABC News has already made significant gains against its network competitors in this category.

News of Sawyer’s move isn’t a shocker. Late last year, she approached James Goldston, currently president of ABC News, to begin a conversation about when would be the best time to step down. Another key part of the sequence occurred in the spring, when Stephanopoulos re-signed with ABC News. As part of that transaction, Stephanopoulos expressed a wish to be deployed as the network’s central anchor in breaking-news situations, according to a network source. “All three got the exact jobs they wanted,” says the source.

As for Sawyer, she’s busy putting together a team that will assist her in compiling the stories she’ll do in her new role. An ABC News spokeswoman didn’t say just how many staffers Sawyer will oversee.

In a place as heavy with egos as a major news network, this arrangement has room for diplomacy. Just how will network bosses decide when Stephanopoulos steps in to take the helm? That is, just how BREAKING must the breaking news be to warrant calling in the chief anchor of ABC News? And what if breaking news emerges during the time that Muir is sitting in the “World News” anchor chair? Can Stephanopoulos step up and bump him? When asked about that one, an ABC News rep had no answer.

Yesterday at around 4 p.m., Goldston, Muir, Sawyer and Stephanopoulos stole away for a glass of champagne to celebrate the moves.