Dick Costolo (l), Adam Bain (r). Photos: Steve Jennings/Getty Images, Romeo Gacad/AFP/Getty Images.

Former Twitter CEO Dick Costolo and former Twitter COO Adam Bain have launched a San Francisco-based startup advisory and investment firm called 01 Advisors, Axios has learned from multiple sources.

The bottom line: Costolo and Bain have been angel investing and advising together for the past couple of years, including in companies like TripActions, but are now formalizing their efforts.

  • 01 Advisors is also raising a fund so that it can get equity beyond "advisory shares." In this way, it's a bit similar to how Tusk Ventures, led by former Uber and Michael Bloomberg campaign adviser Bradley Tusk, operates.
  • Former Twitter investor relations executive David Rivinus is also involved, in addition to Costolo and Bain.

Update: After this story was published, 01 Advisors disclosed in an SEC filing that it has secured $135 million for a fund targeting a total of $200 million.

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