This thread: (https://www.elitetrader.com/et/threads/td-ameritrade-will-offer-btc-futures.315669/) started off as a discussion about TD Ameritrade providing Bitcoin futures trading, but more generally:
Interactive Brokers: long positions only
https://www.interactivebrokers.com/en/index.php?f=25379
https://ibkr.info/article/3049
"Due to the extreme volatility of cryptocurrencies, clients will be unable to assume a short position including as part of a spread. The only time a short order will be allowed will be in the case of a roll trade that results in a long position. In addition, market orders will not be accepted."
https://www.bloomberg.com/news/arti...eek-100-margin-on-some-bitcoin-futures-trades
"Interactive Brokers Group Inc., which has said it handled 53 percent of the first day’s trading in Cboe’s bitcoin futures, will require a margin of 50 percent for long investments, and about 240 percent for short selling, based on current rates, according to Interactive spokeswoman Kalen Holliday."
Looking now at the updated "Knowledge Base" article, (https://ibkr.info/article/3049),
the 240% margin for short positions looks to be based on a flat rate of $40,000 margin for a short position.
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