Wealthfront is rolling in cash. The company announced this morning that it raised $64 million in a Series D round led by Spark Capital. The funding follows closely on the heels of the company’s $35 million Series C in April of this year, a pool of capital that it has yet to even touch, and means that it now has more than $100 million in cash in its war chest.

That's a lot of runway, even at today's burn rates.

The question on most people’s minds this morning is, why? Why raise a follow-up round when you haven’t even dipped into your last one? And how do you put that kind of money to work with any kind of thoughtfulness? I caught up with Wealthfront CEO Adam Nash this morning at the Stocktoberfest conference in Coronado to ask him exactly that.

The short answer, according to Nash, is that the opportunity is big: $7 trillion big, according often-used estimates of the future net worth of the millennial generation. But, by the same token, the competition for these clients is equally massive, coming first and foremost from online brokerage giants Fidelity and Charles Schwab – the latter of which just announced plans to compete directly with Wealthfront in the automated asset management space.

So beefing up Wealthfront’s cash position is largely about giving it the necessary firepower to compete in this market. Nash tells me:

This guarantees us a future of independence. If you want to build a service that’s priced differently and focused on the client, you can’t be beholden to Wall Street. For us this isn’t a short term opportunity, we plan on building this business for decades. We really think the time is right to build a great business in this space. Automated asset management isn’t new. It’s been tried before. But what was missing in the 90’s and during prior iterations of this idea is the millennial generation. This set of 90 million consumers are finally coming of age, and it’s a big enough group to offer the economics around which to build a great business. People forget, Charles Schwab didn’t come from Wall St. Their first clients in the 1970s were in their 20’s. They literally grew up with the Baby Boomer generation, now they manage trillions. We see a similar opportunity with millennials.

Wealthfront is less than three years old, following a pivot from an earlier business, KaChing, but the company has already made a meaningful dent in this market. After taking the first year-and-a-half to reach $500 million in assets under management (AUM), the company has added its next billion over just the last 10 months. By comparison it took Schwab six years to cross the $1 billion threshold.

This speaks to the other explanation for Wealthfront’s most recent raise: It’s capitalizing on momentum -- both its own and that of the broader venture market. The interest was inbound, Nash says. And with many investors predicting a coming economic winter, raising early for a future rainy day seems like a particularly prudent strategy.

“We wanted to take capital off the list of things to worry about,” Nash says. “We never even spent a dollar of last round. But now, we can focus exclusively on product innovation, rather than fundraising. And I have no concerns about Schwab or anyone else outcompeting us on product.”

They key to Wealthfront’s torrid growth, Nash explains, is that the vast majority of its new clients come via word of mouth, both online and offline. Previously, asset management was something that people didn’t talk about, either because money was viewed as a taboo topic or they were afraid of sharing their “secret” to beating the market. Millennials are proving that their attitude toward sharing a good thing is very different. Nash has built his senior leadership team around facilitating this kind of viral growth, hiring veterans from LinkedIn and Facebook with the hopes of importing some of the success from those social giants.

Wealthfront has taken a lot of flack from the traditional asset management community for attempting to automate that which many feel should be a personal, human-powered process. The pejorative term for it and similar businesses is “robo-advisor.” But the growth of Wealthfront’s assets under management and the decision by Schwab to fast-follow it into the market suggests that automated asset management is resonating with consumers and will play at least some role in the future of wealth management.

“When you bet that the future of an industry is one model, if you’re right, eventually everyone will follow you,” Nash says. “I had an all hands with my team yesterday and told them, this is exactly the kind of validation we wanted. Merrill didn’t kill Schwab when it entered the market. But then again, Schwab didn’t kill Merrill. I think there’s an opportunity for the competition to make us all better.”

There is a major demographic split occurring in the financial services space, in Nash’s experience. The Baby Boomer generation is demanding, and frankly is comfortable with, a very different type of customer experience than are Millennials. The younger generation is more concerned with focusing on family, career, and life experience than it is with actively managing its retirement. At the same time, this generation is more distrustful of large institutions – airlines, mobile carriers, banks, etc. – than any generation in history. In this regard, Wealthfront’s promise of low fee, transparent, set it and forget it wealth management is tailor made for this crowd. By the same token, the idea that Schwab can win the trust of this set of consumers seems like a longshot at best.

There are analogies from other industries that suggest Schwab might have a harder time competing on a technology and user experience basis. For example, Amazon wasn’t crushed when Barnes & Noble and WalMart finally decided to launch ecommerce offerings. The same is true of Netflix and Blockbuster. There’s an inherent friction in offline businesses, with their legacy cost structures and organizational hierarchies, trying to shift their business online. Long term, Wealthfront’s biggest competition is likely from its fellow fintech startups like Motif, Robinhood, Quantopian, and others, not from Wall Street.

“Amazon didn’t succeed because the incumbents didn’t enter the ecommerce market,” Nash says. “They succeeded because they were right about market trend, they differentiated through technology, and they were first to build the kind of trust and reputation for this user experience solution that the incumbents couldn’t match or catch up to.”

The other big knock on Wealthfront is that its said to be a low margin business. Not if you think of it like a software company, Nash says. At a 0.25 percent commission on all accounts larger than $10,000, Wealthfront may not be generating Schwab-like fees. But the company earns an average of $200 per account holder per year. “In the software world, $200 per year is a really healthy subscription,” he says. And with the bulk of its new customers acquired at zero cost, this business is scaling more quickly and inexpensively than many realize.

Wealthfront’s new round values the company at $700 million, upping the bar which Nash and his team must clear to deliver what most would considered a successful outcome. As that valuation figure grows, it also starts to limit the potential outcomes available. The list of potential acquirers, for example, just got a lot shorter. Good thing he has the warchest to go big -- now he has to. But, unlike traditional asset managere, big doesn't mean sponsoring sports arenas and buying TV airtime. Rather, it means hiring the smartest engineers possible building better products, while leaving the marketing to its users.

Stocktwits founder and Social Leverage partner asked Nash from stage today how big Wealthfront’s business could be, given the relatively small market caps of traditional wealth management companies like Schwab.

“This is a new animal, an entirely different beast than Schwab,” Nash says. “You would have done a pretty poor job of predicting the market cap of Amazon, by looking at the value of Barnes & Noble. In fact, people told us early on that LinkedIn could never be a big business based on the market cap of Monster. The economics of our business are simply different. At Schwab, 90 percent of their spending goes toward building out retail locations and sales and services. We don’t have that cost structure. I'm hiring engineers and focusing all of our attention on product and user experience. Plus, I think people consistently underestimate how many financial problems people have that can benefit from automation.”