AMNA NAWAZ: Apple is entering a major transition after CEO Tim Cook announced he's stepping down following 15 years at the helm of one of the world's most influential tech companies.

Cook will hand over leadership to John Ternus, the company's head of hardware engineering.

But the handoff comes at a challenging moment for the iPhone and computer giant, as it confronts a series of big questions about its future.

William Brangham has more.

WILLIAM BRANGHAM: During Cook's time at Apple, the company's market value surged by more than 3.6 trillion -- that's trillion with a T -- dollars, thanks in large part to the dominance of the now ubiquitous iPhone.

But starting September 1, John Ternus will step into the top job.

He has spent 25 years leading Apple's engineering team.

That's the one that built products like the iPhone, the iPad and Mac computers.

So, for more on what we can expect from Apple in the coming years, I'm joined by Rolfe Winkler.

He's a technology reporter at The Wall Street Journal who has covered Apple closely.

Rolfe, thank you so much for being here.

Before we get to the new boss, let's talk a little bit about Tim Cook's legacy.

I mean, he took this job arguably handling what was probably the worst -- the hardest succession gig in the tech industry following in the footsteps of the revered visionary Steve Jobs.

How did Tim Cook do?

ROLFE WINKLER, Technology Reporter, The Wall Street Journal: He -- well, it depends on who you ask.

If you ask shareholders, he did pretty well.

You guys mentioned the number, $3.6 trillion of value added during his tenure.

That's pretty impressive.

If you ask others who are looking for innovation, really, truly new products from Apple, they haven't shown us anything certainly as game-changing as the iPhone in certainly ever.

It's, of course, hard to top that.

WILLIAM BRANGHAM: And do we have a sense as to why he's stepping down now?

And he's, I know, staying on as executive chairman.

I take it that's to sort of smooth this transition.

ROLFE WINKLER: Yes, he's going to -- well, first off, why is he stepping down?

He's 65 years old, so it's natural for them to be thinking about succession.

And I think they have been thinking about it for a long time.

Tim Cook, relative to some other CEOs, probably doesn't have as large an ego as some others.

And he cares that Apple is handed off well and smoothly.

And now's a good time.

They're coming off an upgrade cycle.

The iPhone 17 is very popular.

So iPhone sales are good.

Geopolitical issues for the moment have receded, the ones that impact Apple, tariffs, problems with China.

So that's not a big problem.

They have got what they say is a decent product road map.

They're probably referring to things like the foldable iPhone that's coming up, smart glasses that will compete with what Meta's selling.

There's a tabletop robot that is -- they're going to work on that will be powered by a new Siri.

So you put all that together and now's a decent time to be handing the reins to the next guy.

WILLIAM BRANGHAM: And the next guy, John Ternus, is the longtime engineering chief at Apple.

Was he the obvious heir apparent?

And does -- do you have a sense as to how he might steer the company?

ROLFE WINKLER: He led hardware engineering.

He's -- yes, he's -- he makes a lot of sense as a candidate.

There were some others that were interested.

He -- think about what hardware engineering is for this company.

Basically, it's sort of the people who build what the product designers envision.

The hardware engineering team is the one that makes it happen, right?

They're the ones that are responsible for sort of keeping that high-quality bar as high as it is for Apple.

And Ternus has been responsible for doing that for all of its products since 2021.

So he's -- if the future of this company is great devices, and that's the past for this company, it makes sense it's also going to be its future, then Ternus is a natural choice.

WILLIAM BRANGHAM: As you have been describing, we know Apple for the products they make, but so many tech companies are now moving into A.I.

Apple has been slow to do that.

Why is that?

And do you think that that will change under new leadership?

ROLFE WINKLER: I think it has to change under new leadership, because Apple has always led when it comes to the next computing paradigm, whether it was phones or computers before that.

A.I.

is the next shift.

And they're not there.

One reason is because they don't want to spend the money to be there.

These companies are spending hundreds of billions of dollars building large language models.

Apple's not going to spend that.

It prefers buybacks and protecting the bottom line for shareholders.

The other reason that they're struggling there is because they care about privacy, which means they're not using that huge advantage they have, which is all the data on your phone, to build useful A.I.

models.

Now, I think they have got religion on this now, and they're going to try to turn the page and figure out a way to turn their devices into great A.I.

But they really got to move quickly.

WILLIAM BRANGHAM: All right, that is Rolfe Winkler of The Wall Street Journal.

Thank you so much.

ROLFE WINKLER: Thanks for having me.