Junos 12.1R7 will be the last pure 12.1 release for SRX, J-Series and LN. After the release of Junos 12.1R7, any issue found in versions Junos 12.1 will be addressed in a version of Junos 12.1X44. Junos 12.1X44 is an Extended EOL release and as such Juniper will provide support for 36 months through 1/18/16 on this release. Junos 12.1X44 functionality is a superset of Junos 12.1 with EEOL support to provide a long-lived code base allowing customers to standardize on this release.
Juniper is doing everything possible to make this transition as seamless as possible for our customers. If you have any questions or concerns regarding this change please reach out to the SRX PLM department .