The merger will make it the biggest blank-check company deal ever.

Grab's agreement with a special purpose acquisition company (SPAC) backed by Altimeter Capital includes a $4 billion private investment in public equity (PIPE) from a group of Asian and global investors including Fidelity International and Janus Henderson.

Singapore-based Grab declined to comment. There was no response from Silicon Valley-based Altimeter to an emailed request for comment.

The two fund managers also did not respond to an emailed query.

The sources declined to be identified due to the sensitivity of the matter.

The nearly $40 billion valuation is based on a proforma equity value, two of the sources said.

(Reporting by Anshuman Daga; Editing by Muralikumar Anantharaman)

By Anshuman Daga