it is available on EX4300 as you can see below.
root@jtac-ex4300-48t-r2616> request system software add /var/tmp/juniper.conf+.gz ?
Possible completions:
<[Enter]> Execute this command
best-effort-load Load succeeds if at least one statement is valid
delay-restart Don't restart processes
force Force addition of package (ignore warnings)
member Install package on member (0..9)
no-copy Don't save copies of package files
no-validate Don't check compatibility with current configuration
reboot Reboot system after adding package
unlink Remove the package after successful installation
upgrade-with-config-format
validate Check compatibility with current configuration
validate-on-host Validate configuration on host or user@host
validate-on-routing-engine Validate configuration on routing-engine
it is available on all Junos platforms.
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