diff --git a/nix/host-modules/otel.nix b/nix/host-modules/otel.nix
index 66d89855..75e3ec49 100644
--- a/nix/host-modules/otel.nix
+++ b/nix/host-modules/otel.nix
@@ -181,6 +181,23 @@
         let
           otel = config.services.hyperhive.otel;
           listen = "${config.services.hyperhive.network.bridgeIp}:${toString otel.collector.port}";
+          # `otel.protocol` describes the UPSTREAM link and always did.
+          # Inserting a collector splits the path in two, and the
+          # upstream half is the one that has to keep honouring it — so
+          # the exporter is chosen by it, rather than the option quietly
+          # becoming "how agents talk to the collector". The agent half
+          # is pinned to OTLP/HTTP by the receiver below (derived in
+          # hive-c0re/environment.nix).
+          grpcUpstream = otel.protocol == "grpc";
+          upstreamName = if grpcUpstream then "otlp" else "otlphttp";
+          upstream = {
+            endpoint = otel.endpoint;
+            # The value is interpolated by the collector at runtime from
+            # its environment, never by nix. `EnvironmentFile` below is
+            # what puts it there.
+            headers.${otel.collector.upstreamHeaderName} = "\${env:${otel.collector.upstreamHeaderName}}";
+          }
+          // lib.optionalAttrs (otel.protocol == "http/json") { encoding = "json"; };
         in
         {
           assertions = [
@@ -215,16 +232,10 @@
             validateConfigFile = true;
             settings = {
               receivers.otlp.protocols.http.endpoint = listen;
-              exporters.otlphttp = {
-                endpoint = otel.endpoint;
-                # The value is interpolated by the collector at runtime
-                # from its environment, never by nix. `EnvironmentFile`
-                # below is what puts it there.
-                headers.${otel.collector.upstreamHeaderName} = "\${env:${otel.collector.upstreamHeaderName}}";
-              };
+              exporters.${upstreamName} = upstream;
               service.pipelines.metrics = {
                 receivers = [ "otlp" ];
-                exporters = [ "otlphttp" ];
+                exporters = [ upstreamName ];
               };
             };
           };