diff --git a/crates/aisix-core/src/models/passthrough_route.rs b/crates/aisix-core/src/models/passthrough_route.rs
index 8465dcb4..350bee4a 100644
--- a/crates/aisix-core/src/models/passthrough_route.rs
+++ b/crates/aisix-core/src/models/passthrough_route.rs
@@ -379,6 +379,30 @@ pub fn passthrough_route_coupling() -> Value {
                 }
             }
         },
+        // Cross-mode leftovers are configuration errors, not ignored
+        // fields: a companion outside its mode is never consulted, so a
+        // row carrying one is rejected rather than half-honored. The CP
+        // enforces the identical rule on create and patch.
+        {
+            "title": "auth_header_name only in header_key mode",
+            "if": {
+                "anyOf": [
+                    { "title": "auth_mode omitted (defaults to gateway_key)", "not": { "required": ["auth_mode"] } },
+                    { "title": "auth_mode: gateway_key or anonymous", "properties": { "auth_mode": { "enum": ["gateway_key", "anonymous"] } }, "required": ["auth_mode"] }
+                ]
+            },
+            "then": { "not": { "required": ["auth_header_name"] } }
+        },
+        {
+            "title": "anonymous_key_id only in anonymous mode",
+            "if": {
+                "anyOf": [
+                    { "title": "auth_mode omitted (defaults to gateway_key)", "not": { "required": ["auth_mode"] } },
+                    { "title": "auth_mode: gateway_key or header_key", "properties": { "auth_mode": { "enum": ["gateway_key", "header_key"] } }, "required": ["auth_mode"] }
+                ]
+            },
+            "then": { "not": { "required": ["anonymous_key_id"] } }
+        },
         // credential_mode couplings: inject needs a real ProviderKey id; a
         // forward_client route carrying one is a configuration error, not
         // an ignored field.
@@ -516,6 +540,39 @@ mod coupling_tests {
         assert!(validate_passthrough_route(&doc).is_err());
     }
 
+    #[test]
+    fn cross_mode_leftover_companions_are_rejected() {
+        // A companion outside its mode is never consulted at runtime, so
+        // both validators refuse the row instead of half-honoring it.
+        // auth_header_name without header_key (auth_mode absent = gateway_key).
+        let mut doc = base();
+        doc["auth_header_name"] = json!("x-aisix-api-key");
+        assert!(validate_passthrough_route(&doc).is_err());
+        assert!(validate_passthrough_route_lenient(&doc).is_err());
+        // anonymous_key_id on an explicit header_key route.
+        let doc = json!({
+            "name": "r", "path_prefix": "/p",
+            "target_url": "https://u.example", "provider_key_id": "pk",
+            "auth_mode": "header_key", "auth_header_name": "x-aisix-api-key",
+            "anonymous_key_id": "ak-1"
+        });
+        assert!(validate_passthrough_route(&doc).is_err());
+        // auth_header_name on an anonymous route.
+        let doc = json!({
+            "name": "r", "path_prefix": "/p",
+            "target_url": "https://u.example", "provider_key_id": "pk",
+            "auth_mode": "anonymous", "anonymous_key_id": "ak-1",
+            "source_cidrs": ["10.0.0.0/8"],
+            "auth_header_name": "x-aisix-api-key"
+        });
+        assert!(validate_passthrough_route(&doc).is_err());
+        // source_cidrs is deliberately NOT mode-coupled: an extra IP
+        // allowlist is honored on every mode.
+        let mut doc = base();
+        doc["source_cidrs"] = json!(["10.0.0.0/8"]);
+        assert!(validate_passthrough_route(&doc).is_ok());
+    }
+
     #[test]
     fn credential_bearing_header_slots_are_rejected() {
         for field in ["auth_header_name", "identity_header"] {
diff --git a/crates/aisix-obs/src/otlp_http_sink.rs b/crates/aisix-obs/src/otlp_http_sink.rs
index ad3d53c7..d0059f3b 100644
--- a/crates/aisix-obs/src/otlp_http_sink.rs
+++ b/crates/aisix-obs/src/otlp_http_sink.rs
@@ -743,6 +743,16 @@ fn build_otlp_span(record: &SinkRecord, exporter_name: &str) -> Value {
             &event.client_user_agent,
         ));
     }
+    // End-user identity a passthrough route's `identity_header` extracted —
+    // the per-employee attribution of the forward-proxy scenario. Not gated
+    // on the protocol so a future handler that learns to populate it exports
+    // it without touching this sink.
+    if !event.client_identity.is_empty() {
+        attributes.push(attr_string_capped(
+            "aisix.client_identity",
+            &event.client_identity,
+        ));
+    }
     // JWT identity attribution (AISIX-Cloud#564): who the request ran as
     // when it authenticated with a JWT — the identity behind the (possibly
     // shared) api_key_id.
@@ -802,6 +812,14 @@ fn build_otlp_span(record: &SinkRecord, exporter_name: &str) -> Value {
                 attributes.push(attr_string("aisix.mcp.server_name", &event.mcp_server_name));
             }
         }
+        "passthrough" => {
+            if !event.passthrough_route_name.is_empty() {
+                attributes.push(attr_string(
+                    "aisix.passthrough.route_name",
+                    &event.passthrough_route_name,
+                ));
+            }
+        }
         _ => {}
     }
     // Opt-in captured content (#519 B.2) — present ONLY on a record built by
@@ -841,6 +859,7 @@ fn operation_name(event: &UsageEvent) -> &'static str {
     match event.inbound_protocol.as_str() {
         "a2a" => "invoke_agent",
         "mcp" => "execute_tool",
+        "passthrough" => "passthrough",
         _ => "chat",
     }
 }
@@ -867,6 +886,9 @@ fn span_name(event: &UsageEvent) -> String {
     let target = match event.inbound_protocol.as_str() {
         "a2a" => &event.a2a_agent_name,
         "mcp" => &event.mcp_tool_name,
+        // A route name is a registered resource like an agent name, so it is
+        // operator-bounded — but it still passes the length cap below.
+        "passthrough" => &event.passthrough_route_name,
         _ => return "chat.completions".to_string(),
     };
     if target.is_empty() || target.len() > MAX_SPAN_NAME_TARGET {
@@ -1535,6 +1557,44 @@ mod tests {
         assert_eq!(string_at("aisix.a2a.task_state"), "working");
     }
 
+    #[test]
+    fn a_passthrough_relay_exports_route_and_identity_not_a_chat_span() {
+        // The passthrough handler emits usage events with
+        // `inbound_protocol = "passthrough"`; without the explicit branch a
+        // Copilot relay exported as a bare `chat.completions` span with the
+        // route and the device-injected end-user identity recorded nowhere.
+        let mut ev = sample_event();
+        ev.inbound_protocol = "passthrough".into();
+        ev.passthrough_route_name = "copilot-chat".into();
+        ev.client_identity = "alice@example.com".into();
+
+        let body = build_otlp_traces_payload(&ev, "test-exp");
+        let span = &body["resourceSpans"][0]["scopeSpans"][0]["spans"][0];
+        assert_eq!(span["name"], "passthrough copilot-chat");
+        let attrs = span["attributes"].as_array().unwrap();
+        let find = |k: &str| attrs.iter().find(|a| a["key"] == k);
+        let string_at = |k: &str| find(k).unwrap()["value"]["stringValue"].clone();
+        assert_eq!(string_at("gen_ai.operation.name"), "passthrough");
+        assert_eq!(string_at("aisix.passthrough.route_name"), "copilot-chat");
+        assert_eq!(string_at("aisix.client_identity"), "alice@example.com");
+    }
+
+    #[test]
+    fn client_identity_exports_without_a_protocol_gate() {
+        // The identity attribute must not depend on the passthrough branch:
+        // any handler that populates the field gets it exported.
+        let mut ev = sample_event();
+        ev.client_identity = "bob@example.com".into();
+        let body = build_otlp_traces_payload(&ev, "test-exp");
+        let span = &body["resourceSpans"][0]["scopeSpans"][0]["spans"][0];
+        let attrs = span["attributes"].as_array().unwrap();
+        let id = attrs
+            .iter()
+            .find(|a| a["key"] == "aisix.client_identity")
+            .unwrap();
+        assert_eq!(id["value"]["stringValue"], "bob@example.com");
+    }
+
     #[test]
     fn a_streamed_a2a_call_carries_its_event_count() {
         // A unary call has no count, and exporting a zero would read as "the
diff --git a/crates/aisix-proxy/src/attempt.rs b/crates/aisix-proxy/src/attempt.rs
index b434c3e2..42b52a1c 100644
--- a/crates/aisix-proxy/src/attempt.rs
+++ b/crates/aisix-proxy/src/attempt.rs
@@ -291,6 +291,7 @@ pub(crate) fn attempt_reached_upstream(err: &ProxyError) -> bool {
         ProxyError::Bridge(be) => be.reached_upstream(),
         ProxyError::ContentFiltered(_) => true,
         ProxyError::MissingAuth
+        | ProxyError::MissingRouteAuthHeader(_)
         | ProxyError::InvalidApiKey
         | ProxyError::ApiKeyExpired
         | ProxyError::ApiKeyDisabled
diff --git a/crates/aisix-proxy/src/error.rs b/crates/aisix-proxy/src/error.rs
index fbb21333..5e36fef4 100644
--- a/crates/aisix-proxy/src/error.rs
+++ b/crates/aisix-proxy/src/error.rs
@@ -166,6 +166,13 @@ impl ErrorEnvelope {
 pub enum ProxyError {
     #[error("missing or malformed Authorization header")]
     MissingAuth,
+    /// A `header_key` passthrough route saw no gateway key in its configured
+    /// header. Named separately from [`ProxyError::MissingAuth`] because on
+    /// these routes `Authorization` deliberately carries the caller's own
+    /// upstream credential — telling the integrator to fix `Authorization`
+    /// points at exactly the wrong header.
+    #[error("missing or malformed {0} header (this route's gateway API key header)")]
+    MissingRouteAuthHeader(String),
     #[error("invalid API key")]
     InvalidApiKey,
     /// The presented key exists but its `expires_at` deadline has
@@ -336,7 +343,8 @@ pub(crate) fn guardrail_block_message(side: &str, guardrail_name: Option<&str>)
 impl ProxyError {
     pub fn status(&self) -> StatusCode {
         match self {
-            ProxyError::MissingAuth
+            ProxyError::MissingRouteAuthHeader(_)
+            | ProxyError::MissingAuth
             | ProxyError::InvalidApiKey
             | ProxyError::ApiKeyExpired
             | ProxyError::ApiKeyDisabled
@@ -369,7 +377,8 @@ impl ProxyError {
 
     pub fn kind(&self) -> &'static str {
         match self {
-            ProxyError::MissingAuth
+            ProxyError::MissingRouteAuthHeader(_)
+            | ProxyError::MissingAuth
             | ProxyError::InvalidApiKey
             | ProxyError::ApiKeyExpired
             | ProxyError::ApiKeyDisabled
diff --git a/crates/aisix-proxy/src/passthrough_route.rs b/crates/aisix-proxy/src/passthrough_route.rs
index a9512038..809024ac 100644
--- a/crates/aisix-proxy/src/passthrough_route.rs
+++ b/crates/aisix-proxy/src/passthrough_route.rs
@@ -352,10 +352,7 @@ pub async fn entry(
                 status,
                 elapsed,
             );
-            crate::usage_attr::emit_error_usage_event(
-                &state,
-                &snapshot,
-                "passthrough_route",
+            let mut event = crate::usage_attr::build_error_usage_event(
                 "passthrough",
                 &request_id,
                 "",
@@ -364,6 +361,16 @@ pub async fn entry(
                 error.kind(),
                 &client,
             );
+            // The route matched before the pipeline failed, so a rejected
+            // request still attributes to it — an operator triaging 401s
+            // per route needs the name on the event, not just in the log.
+            event.passthrough_route_name = route_name.clone();
+            crate::usage_attr::emit_prepared_usage_event(
+                &state,
+                &snapshot,
+                "passthrough_route",
+                event,
+            );
             error.into_response()
         }
     }
@@ -917,7 +924,7 @@ async fn authenticate(
                 .and_then(|v| v.to_str().ok())
                 .map(|v| v.strip_prefix("Bearer ").unwrap_or(v).trim().to_string())
                 .filter(|v| !v.is_empty())
-                .ok_or(ProxyError::MissingAuth)?;
+                .ok_or_else(|| ProxyError::MissingRouteAuthHeader(name.to_string()))?;
             crate::auth::authenticate_token(state, &token, ctx).await
         }
         PassthroughAuthMode::Anonymous => {
diff --git a/crates/aisix-proxy/src/usage_attr.rs b/crates/aisix-proxy/src/usage_attr.rs
index 95afed50..69481c6a 100644
--- a/crates/aisix-proxy/src/usage_attr.rs
+++ b/crates/aisix-proxy/src/usage_attr.rs
@@ -354,6 +354,30 @@ pub(crate) fn emit_error_usage_event(
     error_class: &str,
     client: &ClientContext,
 ) {
+    let event = build_error_usage_event(
+        inbound_protocol,
+        request_id,
+        requested_model,
+        api_key_id,
+        status_code,
+        error_class,
+        client,
+    );
+    emit_prepared_usage_event(state, snap, label, event);
+}
+
+/// The [`emit_error_usage_event`] event without the emission, for a caller
+/// that attributes handler-specific fields (e.g. the passthrough route name)
+/// before handing it to [`emit_prepared_usage_event`].
+pub(crate) fn build_error_usage_event(
+    inbound_protocol: &'static str,
+    request_id: &str,
+    requested_model: &str,
+    api_key_id: &str,
+    status_code: u16,
+    error_class: &str,
+    client: &ClientContext,
+) -> UsageEvent {
     let mut event = UsageEvent {
         request_id: request_id.to_string(),
         occurred_at: chrono::Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Secs, true),
@@ -367,6 +391,15 @@ pub(crate) fn emit_error_usage_event(
         ..Default::default()
     };
     apply_jwt_identity(&mut event, client.jwt.as_ref());
+    event
+}
+
+pub(crate) fn emit_prepared_usage_event(
+    state: &ProxyState,
+    snap: &AisixSnapshot,
+    label: &'static str,
+    event: UsageEvent,
+) {
     state.usage_sink.try_emit(label, event.clone());
     let exporters = live_exporters(state, snap);
     state
diff --git a/schemas/resources/passthrough_route.schema.json b/schemas/resources/passthrough_route.schema.json
index 2fcc6f53..9a7c7caa 100644
--- a/schemas/resources/passthrough_route.schema.json
+++ b/schemas/resources/passthrough_route.schema.json
@@ -240,6 +240,78 @@
         ]
       }
     },
+    {
+      "if": {
+        "anyOf": [
+          {
+            "not": {
+              "required": [
+                "auth_mode"
+              ]
+            },
+            "title": "auth_mode omitted (defaults to gateway_key)"
+          },
+          {
+            "properties": {
+              "auth_mode": {
+                "enum": [
+                  "gateway_key",
+                  "anonymous"
+                ]
+              }
+            },
+            "required": [
+              "auth_mode"
+            ],
+            "title": "auth_mode: gateway_key or anonymous"
+          }
+        ]
+      },
+      "then": {
+        "not": {
+          "required": [
+            "auth_header_name"
+          ]
+        }
+      },
+      "title": "auth_header_name only in header_key mode"
+    },
+    {
+      "if": {
+        "anyOf": [
+          {
+            "not": {
+              "required": [
+                "auth_mode"
+              ]
+            },
+            "title": "auth_mode omitted (defaults to gateway_key)"
+          },
+          {
+            "properties": {
+              "auth_mode": {
+                "enum": [
+                  "gateway_key",
+                  "header_key"
+                ]
+              }
+            },
+            "required": [
+              "auth_mode"
+            ],
+            "title": "auth_mode: gateway_key or header_key"
+          }
+        ]
+      },
+      "then": {
+        "not": {
+          "required": [
+            "anonymous_key_id"
+          ]
+        }
+      },
+      "title": "anonymous_key_id only in anonymous mode"
+    },
     {
       "if": {
         "anyOf": [
diff --git a/tests/e2e/src/cases/passthrough-route-e2e.test.ts b/tests/e2e/src/cases/passthrough-route-e2e.test.ts
index d7f6c65b..e9676fe1 100644
--- a/tests/e2e/src/cases/passthrough-route-e2e.test.ts
+++ b/tests/e2e/src/cases/passthrough-route-e2e.test.ts
@@ -281,6 +281,25 @@ describe("passthrough-route e2e: explicit routes, BYO credentials, 410 tombstone
     // …and the gateway's side-channel headers did not.
     expect(hit.headers["x-aisix-api-key"]).toBeUndefined();
     expect(hit.headers["x-aisix-user"]).toBeUndefined();
+
+    // Missing gateway key: the 401 must point at the route's configured
+    // header, not `Authorization` — on this route Authorization carries the
+    // caller's own upstream credential and is exactly the wrong thing to fix.
+    const noKey = await harnessRequest(`${app!.proxyUrl}/v1/chat/completions`, {
+      method: "POST",
+      headers: {
+        host: "ai-upstream.example.com",
+        authorization: "Bearer employee-official-token",
+        "content-type": "application/json",
+      },
+      body: JSON.stringify({ model: "gpt-4o", messages: [] }),
+    });
+    expect(noKey.statusCode).toBe(401);
+    const noKeyBody = (await noKey.body.json()) as {
+      error?: { message?: string };
+    };
+    expect(noKeyBody.error?.message).toContain("x-aisix-api-key");
+    expect(noKeyBody.error?.message).not.toContain("Authorization");
   });
 
   test("anonymous route binds the configured principal behind source_cidrs", async (ctx) => {