Solaris 10 was originally launched in January 2005, and over it’s lifespan has introduced a ton of ground breaking features, like the ZFS volume manager/filesystem, DTrace, Zones, Service Management Facility, Trusted Extensions and more. But eventually all good things must some to an end, and with the launch of Solaris 11 in 2010, it has become time for Oracle to start the process to move Solaris 10 to its expected end of life in 2021.
To start the process, at the beginning on 2018, Solaris 10 entered extended support. Extended support is basically the same as Premier Support, other than a few major changes. First, there is a support uplift with Extended Support, if you need Solaris 10, expect to pay a little more for support. Also Extended Support is more about providing a bridge to the Sustaining support stage, so it includes limited bug fixes with less commitment to interoperability updates and third party platform certifications.Now it is not all doom and gloom, you still can call for help, and all the normal support streams like MOS are still available. The official changes can be found in Doc ID 1272947.1
This is all good, but there is still a need for Oracle customers to access patches that were available before Solaris 10 went into Extended Support. This is especially useful when you need to patch Solaris 10 so P2V migrations can be performed when moving to new servers like the M12-2. The patch set is now available in MOS as a Patchset CPU, which can be downloaded from here. As part of the move to Extended Support, Solaris 10 patchsets are released on a quarterly basis, so if you have opted for Extended Support, plan on downloading once a quarter.
That being said, if you are on Solaris 10, you really should consider moving to Solaris 11, there are even more features in Solaris 11. and Solaris 11 development is still ongoing, with 11.4 released to Open BETA not long ago.