Bill Ackman's special purpose acquisition company, Pershing Square Tontine Holdings, raised its IPO target to $4 billion from $3 billion, according to a Monday regulatory filing. The SPAC now aims to go public with 200 million units priced at $20 each. The new target should set a fresh record for SPAC IPO proceeds. Ackman hasn't yet revealed which company he aims to buy following the offering, but his firm has revealed interest in "high-quality, venture-backed businesses" otherwise deemed "mature unicorns." Visit the Business Insider homepage for more stories.