Google is buying an arm of Twitter that makes software tools for mobile app developers, shifting a Boston-area engineering team to a new corporate parent as financially troubled Twitter continues shedding assets and executives.

The companies announced the deal Wednesday. It was not immediately clear how many Twitter employees would join Google, and financial terms were not disclosed.

“As we embark on 2017, we are focusing on our core products and business to best position Twitter for long-term growth,’’ chief executive Jack Dorsey said in a blog post. Twitter said it will retain an undisclosed number of employees at its Cambridge office, working on projects that include data science and live video.

Twitter’s developer-software tools division, headquartered in Cambridge, is called Fabric. It was created after Twitter’s 2013 acquisition of Crashlytics, a Cambridge mobile-app developer software startup, in a cash-and-stock deal worth about $300 million.

Former Crashlytics executives took on prominent roles at Twitter after the acquisition. The most notable was Crashlytics cofounder Jeff Seibert, who became a senior product director. On Wednesday, he said that he is leaving the company.

Former Crashlytics engineering director Rich Paret stayed in Cambridge to oversee Fabric and several other projects as a Twitter vice president. In a blog post Wednesday, Paret said Fabric’s services are now used on 2.5 billion mobile devices.

The sale comes as Twitter struggles to add large numbers of users and beef up its digital advertising business. In October, the company announced plans to lay off about 350 people, and several executives left in 2016. This week, Twitter shut down Vine, a short-form video app.

Twitter has been the subject of acquisition rumors for months. Its stock, which traded above $50 per share less than two years ago, closed at $17.11 Wednesday, up 0.9 percent.

Curt Woodward can be reached at curt.woodward@globe.com. Follow him on Twitter @curtwoodward.