Zabbix agents starting with version 1.4 are compatible with Zabbix 4.0. However, you may need to review the configuration of older agents as some parameters have changed, for example, parameters related to logging for versions before 3.0.
To take full advantage of new and improved items, improved performance and reduced memory usage, use the latest 4.0 agent.
Note that Zabbix agent newer than 4.0 cannot be used with Zabbix server 4.0.
Zabbix 4.0.x server can only work with Zabbix 4.0.x proxies. Zabbix 4.0.x proxies can only work with Zabbix 4.0.x server.
Warnings about using incompatible Zabbix daemon versions are logged since Zabbix 4.0.8.
XML files, exported with 1.8, 2.0, 2.2, 2.4, 3.0, 3.2 and 3.4 are supported for import in Zabbix 4.0.