Dual Core 4, or DC4, is the newest polyphasic schedule in the Dual Core family of schedules. However, similar to Dual Core 3, it also has 2 core sleeps of one-cycle length each, with the addition of one nap. The total sleep is 4 hours and 20 minutes, which hovers around the very bare minimum amount for adaptability.
As a typical Dual Core schedule, DC4 inherits all the characteristics from Segmented sleep, with the repartitioning of SWS and REM into respective core sleeps. The last nap, being placed around 6 PM, is intended to provide more alertness. While looking very similar to DC3, the purpose of DC4 is to transition to Uberman sleep, with 2 core sleeps to eventually be reduced to 2 20m naps. To prepare for the transition, all sleep blocks on DC4 look equidistant in scheduling to resemble the wake gap between each nap on Uberman, which is approximately ~3h40m to 4h.
Because of the 2 core sleeps, which facilitate ideally all SWS, the remaining naps provide REM sleep to keep a healthy balance of homeostatic pressure. The first nap is expected to be teemed with REM sleep, thanks to its position in REM peak. Other naps provide potentially less amount of REM sleep, as well as some NREM2.
Although DC4 even has more sleep than DC3, up to date no one has successfully adapted to DC4. Attempts are very rare. There used to be one attempt that almost resulted in a successful adaptation by the inventor of this schedule, but he had to quit due to the entanglement of some medicine use. It may even be more difficult than DC3, because of the extra nap that will stagnate sleep onset, and it will likely take longer for naps on this schedule to stick. The other sleep blocks closely resemble DC3, so this adaptation will be along the lines of E3/Bimaxion, if not more difficult to manage. SWS and REM wakes during the cores will be intensified during stage 3, and extensive alarm setup is required. The sharp repartitioning of sleep stages at first may induce SWS into the 2 afternoon naps, causing a lot of grogginess upon awakening.
Because DC4 is intended to be a transitional schedule to Uberman, it is not considered a long-term schedule. The wake gap between each sleep is too small for most real-life activities, with the comprehensive forfeit of social life. While posing a Uberman-rhythm between each sleep and the total sleep appears to be sustainable for an extended period of time, the clumsiness in scheduling just adds to the burdens. DC4 is vastly inferior to DC3, and the transition to Uberman can take several months. So far, it remains a hypothetical polyphasic schedule that has not been far from being fully tested, and notably no one has adapted to Uberman from this schedule, either.
With all the downsides, DC4's use is mostly to learn to nap with the high number of naps per day. It can be used as a less extreme form of Naptation thanks to 2 core sleeps. Sleepers can choose to start this schedule temporarily as a way to learn how to learn the short naps, recover on monophasic afterwards, and start a polyphasic attempt anew, including Uberman if desired. DC4 may also act as a fallback schedule if Uberman or E5 happens to fail, but no one has pulled this off so far. With everything being mostly hypothetical, there is little to no use in attempting this schedule. DC3 would be the more preferable choice.