X-Cache-Hits
List indicating number of cache hits in each node.
Fastly writes this header into responses. It is proprietary to Fastly.
Fastly appends this non-standard header to responses by default, and sets it to the value of obj.hits.
The hit count is per-cache-server, not per-data-center, and cache hits will not be evenly distributed across cache nodes due to clustering, making this value of very limited use in most cases.
This header may report results from multiple cache servers, if shielding or Next-gen WAF at Edge is enabled, or if you use custom VCL code that invokes the restart statement.
Other than in the case of a restart, any positive value in this header indicates that the request was satisfied from cache and not forwarded to origin (or Next-gen WAF at Edge)
You can remove this header, or make it subject to Fastly-Debug, by using VCL in the vcl_deliver subroutine (after the #FASTLY deliver placeholder in custom VCL, or in a 'deliver' VCL snippet):
if (!req.http.Fastly-Debug) { unset resp.http.X-Cache-Hits;}