Which datatype to use for field @version?

using the usual™ ELK-Stack we see a field conflict in Kibana for the field "@version".

Since this blocks our migration to Elasticsearch 2.x, I'd like to create a field mapping for "@version", but with which datatype? long or string (analyzed:false) ?

Logstash: 1.5.x
Elasticsearch: 1.7.x

AFAICT that field has always been a string.

I thought about setting this field to long since the default value was integer.

Right now we won't use the field anyway, just asking to improve our index mappings and make this more static/stable. Looks like we also will stick to string then.

Thank you.