The core systems market in the U.S. has long been dominated by a small group of vendors. But that may be about to change.

Core systems startups are chasing U.S. banks. And now several well-established foreign-based core providers are pursuing U.S. clients.

The opportunity is huge. Half of the tech spending for banks worldwide comes from the U.S., said Jay Mossman, the North American regional chief executive for Temenos Group in Switzerland.

The competition is fierce as the incumbents have a long and often tangled relationship with banks.

Also, banks are typically terrified about the idea of ripping out and replacing the guts of their institution, but many realize that their ability to serve the digital demands of their clients and take advantage of things like application programming interfaces and cloud technology is constrained by legacy technology. The foreign-based firms see that conundrum as their way in.

"In the U.S., banks see core systems as a commodity, and in other countries they see it as a way to power innovation," said Falk Rieker, global head of banking for the German tech giant SAP. "To achieve the digital customer experience everyone wants, you need an agile, open tech platform. Banks should be investing now."

Like SAP, Temenos is also aggressively targeting the U.S.

"Our No. 1 strategic goal right now is in the U.S.," Mossman said. "We have tried on a couple of occasions in the past, but it was just sending over an executive or two and sticking our toe in the water."

The ramped-up effort seems to be paying off; Mossman said Temenos has poached a "large, retail bank" from one of the "Big Three" core vendors, referring to Fiserv, FIS and Jack Henry, to use its T24 core banking software. Mossman said the contract is being finalized and that an announcement would likely come "within 60 days."

As part of its renewed focus on the U.S. market, Temenos turned to acquisitions, buying TriNovus, a compliance software firm, and Akcelerant, a provider of software for loans, collections and risk management. (Mossman founded Akcelerant.)

The deals gave Temenos a valuable entry point to reaching domestic banks. But getting U.S. banks to switch their core providers is still a difficult proposition because of the incumbents and the magnitude of negotiating a core-processing deal, Mossman said.

"We have a good pipeline [of banks Temenos is talking to], but it's such a long, drawn-out process," he said. "Still, we're seeing more banks willing to have this conversation than 12 to 18 months ago."

He said Temenos' infrastructure is based on application programming interfaces. That makes it appealing because banks, particularly larger ones, are looking for "progressive renovation" when it comes to core systems replacement. In other words, Temenos' system allows for a gradual replacement.

"From a tech perspective, you don't have to go through a full, big-bang type of implementation," he said.

SAP is also making a pointed effort to break into the U.S. The firm's financial services unit is a small but growing part of its overall business, counting Standard Bank of South Africa and Sberbank of Russia among its clients.

But the company is looking to 2017 and beyond to make a big push in the U.S., as more banks here embrace cloud technology, APIs and the concept of open banking, Rieker said.

To that end, SAP made upgrades to its most recent core solution, called Banking Services 9.0, to embrace APIs, Rieker said. It features applications that can be layered on top of existing technology to enable real-time digital banking, he said.

"Customers can implement these new features without going through a lengthy release upgrade processes, thereby reducing cost as well as time to market," Rieker said.

Other non-U.S.-based core providers are getting in on the game as well. Goldman Sachs recently announced that it is using software from the Indian technology firm Infosys to power Marcus, the online lending subsidiary it launched two months ago.

One company that straddles both the startup and global core vendor worlds is Leveris, which launched this year after spending three years building a core banking and lending platform. Its chief technology officer and several engineers previously helped build Air Bank, a startup digital bank in the Czech Republic. The Irish company already has a "healthy pipeline in Europe and southeast Asia, but we are speaking with a few banks in the U.S. already," said Aidan Lawlor, Leveris' head of marketing.

Global core vendors in general are making greater efforts to make inroads in the U.S. banking industry, said Brad Smith, managing director with Cornerstone Advisors.

"The sales calling efforts" from non-U.S. core providers "seem to have become more aggressive overall and more aggressive downstream, calling on smaller banks as well as the big ones," he said. "Banks are starting to hear more from companies like Temenos and SAP and others."

Even though these firms can point to the many banks around the world using their core software, they still face a hurdle in convincing U.S. institutions that their technology can comply with this country's unique regulatory structure, Smith said.

"Banks are asking the question: can these international products help us comply with the multitude of state and federal regulations?" he said. "To take a flier on a system not yet proven in the U.S., that's a risk profile a lot of CIOs – or CEOs or CFOs – don't have yet. They don't want to be first, but they very well might be interested in being seventh or tenth."

However, there's one outside core vendor that has seemingly already passed this test. Perhaps the most notable example of a foreign core provider's platform being used in a U.S. bank is Tata Consultancy Services of India, which in 2013 announced that the $55 billion-asset Zions Bancorp. would implement its TCS BaNCS core technology. Also noteworthy is the Spanish Bank BBVA's 2011 announcement that its U.S. subsidiary Compass would adopt Accenture's Alnova core banking product. The bank had already been using Alnova in nine other countries.

"Apart from getting our name out there, it showed that a U.S. bank had a comfort level with us, and validated that our product is compliance-ready," for U.S. banking regulations, said Ashvini Saxena, head of America for TCS.

Still, even with that recognition, even TCS finds it difficult to spur U.S. banks from their inertia on replacing core systems.

Banks' technology infrastructure is "a set of solutions built over a period of time. It's a very complex environment they have and they're scared of touching something as big as this," he said.

Banks want to meet the digital demands of its customers, Saxena said. However, rather than replacing a core system, they look for incremental patches.

"They add front-end applications. But you can't keep doing that," Saxena said. "If a bank really wants to be a nimble and digital enterprise, it can't become that without touching the core applications."

Request for comment to FIS and Jack Henry were not immediately returned, but Fiserv said it is developing technology to serve the banks' needs of the future.

"Fiserv is uniquely positioned to bring value to our clients not only through the depth of the solution set we bring to the table, but on the ability to offer new capabilities like card controls and real-time alerts that are built around data from the core platform," Byron Vielehr, Fiserv's president for depository institution services, said in an email. "We are continually exploring and actively evaluating the different ways new technologies – including cloud-based services – can drive enhanced value for our clients and their customers."