[andrewla]

The implied price of tether by comparing the price of BTCUSDT vs BTCUSD (and, for that matter, all XXXUSDT and XXXUSD pairs) is consistent with the price indicated on Kraken. That exchange, as far as I'm aware, is the only USDUSDT exchange operating currently.

    At 2018-10-15T13:33:24Z:
    Kraken    USDTZUSD:    0.9248
    Gemini    BTCUSD:   6384.0
    Bitfinex  BTCUSDT:  6925.1
    G / bfx   USDTUSD:     0.9218

Technically, Bitfinex operates a USDUSDT exchange (at 1:1), but they are reporting banking problems [1], and its possible that liquidity flight is driving some of the differential. Their exchange is de facto BTCUSDT since Tether is the fastest path to USD liquidity available, especially at the moment.

[1] https://medium.com/bitfinex/fiat-deposit-update-october-15th...