If and only if the difficulty remains constant, the green, blue and red arrow indicate the price required to cover the marginal costs of BTC production with the Antminer S9, S15 and S17 respectively.
Furthermore the marginal costs for the Antminer 19 Pro are also plotted. The S19 is is expected to be released in May 2020.
Prices below those levels would imply miner losses. Even if miners believe in rising prices, it would be cheaper for them to buy BTC rather than to mine. After halving, the difficulty (or hashrate) would have to half in order to cover the marginal costs of S17 miners at current BTC prices.
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