Which releases are supported for coexistence, fallback, and migration?

z/OS® V2R1 is coexistence, fallback, and migration supported with the following z/OS releases: V2R1, V1R13, and V1R12. This means that:

Coexistence of a V2R1 system with a V1R13 and V1R12 system is supported.
Fallback from a V2R1 system to a V1R13 or V1R12 system is supported.
Migration to a V2R1 system from a V1R13 or V1R12 system is supported.

Before z/OS V1R6, four consecutive releases were supported for coexistence, fallback, and migration. Starting with z/OS V1R6, the coexistence, fallback, and migration policy was aligned with the service policy. Because the service policy is a 3-year policy (described in Service policy), and because V1R6 was the start of the annual release cycle, as a general rule, three releases are supported for coexistence, fallback, and migration over a period of three years. You can think of this as an "n-2" rule, where n is the latest release. Thus, V2R1 minus 2 = R12 meaning that R12 is the earliest (oldest) release supported for coexistence, fallback, and migration with V2R1.

The current policy represents an increase of one year over the two-year period provided by the previous coexistence, fallback, and migration policy of four releases under a six-month release cycle. The intention of the current policy is to simplify and provide greater predictability to aid in release migrations.

Exceptions are:

In some cases, more than three releases may be coexistence, fallback, and migration supported if IBM® at its sole discretion chooses to provide service support for greater than three years for a release.
Any z/OS release having three or fewer months of service remaining at general availability of a new release will not be coexistence, fallback, or migration supported with the new release.

The z/OS coexistence, fallback, and migration policy applies to the elements and features of z/OS, not to customer-developed applications, vendor-developed applications, or IBM products that run on z/OS.

IBM performs platform (integration) testing and will provide service as necessary to support the z/OS coexistence, fallback, and migration policy.

See Table 1 for a summary of coexistence, fallback, and migration support for recent, current, and upcoming releases.

These statements represent the current intentions of IBM. IBM reserves the right to change or alter the coexistence, fallback, and migration policy in the future or to exclude certain releases beyond those stated. IBM development plans are subject to change or withdrawal without further notice. Any reliance on this statement of direction is at the relying party's sole risk and does not create any liability or obligation for IBM.

Table 1. Coexistence, fallback, and migration support for recent, current, and upcoming releases
z/OS release (see note 1)	Releases that are coexistence, fallback, and migration supported with the release in column one (see note 1)	Explanation (see note 2)
R6	R6, R5, R4, R3	General availability of R6 was September 2004. R2 was the oldest service-supported release at that time and therefore the oldest release that would be coexistence, fallback, and migration supported. However, its end-of-service date (October 2004) was within three months of R6 general availability (September 2004), so R3 became the oldest release supported for coexistence, fallback, and migration with R6.
R7	R7, R6, R5, R4	General availability of R7 was September 2005. R4 was the oldest release that was service supported at that time and therefore the oldest release supported for coexistence, fallback, and migration with R7.
R8	R8, R7, R6, R5	General availability of R8 was September 2006. R4 was the oldest release that was service supported at that time because its end-of-service date was extended by 18 months to 31 March 2007. However, R4 was not coexistence, fallback, and migration supported with R8. Therefore, R5 became the oldest release supported for coexistence, fallback, and migration with R8.
R9	R9, R8, R7	General availability of R9 was September 2007. R7 was the oldest release that was service supported at that time and therefore the oldest release supported for coexistence, fallback, and migration with R9.
R10	R10, R9, R8	General availability of R10 was September 2008. R8 was the oldest release that was service supported at that time and therefore the oldest release supported for coexistence, fallback, and migration with R10.
R11	R11, R10, R9	General availability of R11 was September 2009. R9 was the oldest release that was service supported at that time and therefore the oldest release supported for coexistence, fallback, and migration with R11.
R12	R12, R11, R10	General availability of R12 was September 2010. R10 was the oldest release that was service supported at that time and therefore the oldest release supported for coexistence, fallback, and migration with R12.
R13	R13, R12, R11	General availability of R13 was September 2011. R11 was the oldest release service supported at that time and therefore the oldest release supported for coexistence, fallback, and migration with R13.
V2R1	V2R1, V1R13, V1R12	General availability of V2R1 was September 2013. V1R12 was the oldest release service supported at that time, and therefore the oldest release supported for coexistence, fallback, and migration with V2R1.

Note:

For readability, the version numbers have been omitted from the releases shown. Also, release numbering of future releases (later than R13) is for illustrative purposes and is not a guarantee of actual release numbers.
Future general availability (GA) dates are projections based on a two-year release cycle (described in Two-year release cycle). Future end of service (EOS) dates are projections based on the 3-year service policy (described in Service policy).