According to CNBC, the biggest options trade on the Cboe VIX Index on Tuesday was an unusual $6 million purchase of deep in-the-money puts that may have been a rate-related bet ahead of Wednesday's Federal Reserve decision. Around 10 a.m. Chicago time, a trader bought 563 110-strike VIX puts expiring Oct. 21 for $5.1 million and $1.2 million of 130-strike puts expiring Nov. 18, with the VIX ending the session at 17.2.

The 110-strike puts cost $91 each and the 130-strike puts cost $110 each, putting the trade's breakeven at a little over $19. Noel Smith, founder and chief investment officer of Convex Asset Management, said the position could be part of a broader hedge involving short calls and futures. Brent Kochuba of SpotGamma said the trade may be aimed at exploiting the spread between VIX options and futures.