An index trader’s week has always had a hole in it. Futures stop on Friday evening and restart on Sunday evening, and in between there is news and no price. The first print on Sunday night arrives all at once, as a gap.
That hole now has a live market in it. Perpetual contracts on the S&P 500 and the Nasdaq 100 trade around the clock on Hyperliquid, weekends included. Their move since Friday’s close is the implied open.
How it is measured
The number is the perp’s price now against the perp’s own price at the last cash close. It is anchored to the perp’s own print at the bell, taken from the candle that ends there. That matters because a perp carries a standing difference to the index it tracks. Measuring the perp against itself cancels that difference, so the result is the move and nothing else.
If the perp has no print at the bell, there is no anchor and no number. A figure built on a stale anchor would look precise and be wrong.
What it is
It is a market price on another venue. Real traders with real money have the S&P 500 perp up or down by that much since Friday. On 4 October 2026 that market held about $349 million of open interest, so it is a market with weight behind it.
What it is not
It is not a forecast, and the difference is practical. Weekend depth is thinner than weekday depth. A move on thin depth can be one large order. When futures reopen, a much deeper market gets its say, and the two can disagree. The honest sentence is that the perps have the index up a tenth of a percent. The dishonest one is any promise about Monday’s first print.
It also says nothing about small caps. No liquid perp exists on the Russell 2000, so there is no implied open for IWM. Borrowing the S&P 500’s move would be inventing a number.
Which names are carrying it
An index move is the sum of its members, and a handful of members carry most of the weight. The seven largest names in both indexes each have a perp that trades through the weekend. Measured the same way, they show which names are behind the index move. If the index perp is up and one mega-cap accounts for most of it, that is a different Monday from one where all seven are up together.
Using it with the dealer map
The implied open tells you where the perps have price. The dealer map tells you what that level means: above or below the gamma flip, near a wall, inside the expected move. A weekend move that carries SPY across the flip changes the character of Monday’s open, which is the idea in the dealer map after an overnight gap. The Trader dashboard shows the implied open beside the map and sends a push when an index perp moves half a percent while the market is shut.