That seems pretty high to me though, you can arbitrage on Coinbase and Gemini which are both US based regulated exchanges (they have licenses, insurance, and audits) with what I would expect to be less than 7%/month risk. Perhaps there just aren't many arbitragers with access to the futures market and knowledge of Gemini/Coinbase yet. I'd arbitrage it myself but I have no retail brokerage access to shorting the future contracts.
Further evidence the market just isn't acting efficiently yet: volume of 3.43k contracts today, which is only $61M. The 24 hour trade volume of the top 5 Bitcoin exchanges is $5 billion.
> Right now 1 BTC on Gemini (the reference exchange for CBOE Bitcoin futures) is $16,600 and the futures price is $17,800 for a 1 or 2 month contract.
> Since the risk free rate is about 0.125% monthly and this spread is 7.2%,
> it looks like the market is pricing the counter-party risk at about 7% for one or two month durations.