diff --git a/CHANGELOG.md b/CHANGELOG.md
index c850c81985..8d285ce0fb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * General
   * Stop reporting db file sizes during init phase ([#3331](https://github.com/mozilla/glean/pull/3331))
   * Tiny performance improvement for putting tasks on the dispatcher ([#3318](https://github.com/mozilla/glean/pull/3318))
+  * Instrument the case when the `client_id.txt` file does not exist yet ([#3339](https://github.com/mozilla/glean/pull/3339))
 
 # v66.1.2 (2025-11-25)
 
diff --git a/glean-core/metrics.yaml b/glean-core/metrics.yaml
index eda34050ed..0e559ec806 100644
--- a/glean-core/metrics.yaml
+++ b/glean-core/metrics.yaml
@@ -1188,6 +1188,7 @@ glean.health:
       - permission-denied
       - io
       - c0ffee-in-file
+      - file-not-found
 
   file_write_error:
     type: labeled_counter
diff --git a/glean-core/src/core/mod.rs b/glean-core/src/core/mod.rs
index 5baa278a40..fd5866a80f 100644
--- a/glean-core/src/core/mod.rs
+++ b/glean-core/src/core/mod.rs
@@ -299,6 +299,11 @@ impl Glean {
             Ok(id) => Some(id),
             Err(ClientIdFileError::NotFound) => {
                 // That's ok, the file might just not exist yet.
+                glean
+                    .health_metrics
+                    .file_read_error
+                    .get("file-not-found")
+                    .add_sync(&glean, 1);
                 None
             }
             Err(ClientIdFileError::PermissionDenied) => {
diff --git a/glean-core/src/internal_metrics.rs b/glean-core/src/internal_metrics.rs
index ebc5fbd9ce..b0e405f64b 100644
--- a/glean-core/src/internal_metrics.rs
+++ b/glean-core/src/internal_metrics.rs
@@ -467,6 +467,7 @@ impl HealthMetrics {
                     Cow::from("permission-denied"),
                     Cow::from("io"),
                     Cow::from("c0ffee-in-file"),
+                    Cow::from("file-not-found"),
                 ]),
             ),
             file_write_error: LabeledMetric::<CounterMetric>::new(
diff --git a/glean-core/tests/clientid_textfile.rs b/glean-core/tests/clientid_textfile.rs
index 05f585ec25..11133f4a36 100644
--- a/glean-core/tests/clientid_textfile.rs
+++ b/glean-core/tests/clientid_textfile.rs
@@ -441,6 +441,25 @@ mod read_errors {
             .unwrap();
         assert_eq!(1, state);
     }
+
+    #[test]
+    fn file_not_found_is_reported() {
+        let (glean, temp) = new_glean(None);
+
+        glean.submit_ping_by_name("health", Some("pre_init"));
+        let mut pending = get_queued_pings(temp.path()).unwrap();
+        assert_eq!(1, pending.len());
+        let payload = pending.pop().unwrap().1;
+
+        let state = &payload["metrics"]["string"]["glean.health.exception_state"];
+        assert_eq!(&serde_json::Value::Null, state);
+
+        let state = payload["metrics"]["labeled_counter"]["glean.health.file_read_error"]
+            ["file-not-found"]
+            .as_i64()
+            .unwrap();
+        assert_eq!(1, state);
+    }
 }
 
 mod write_errors {