diff --git a/datadog-sidecar-ffi/src/lib.rs b/datadog-sidecar-ffi/src/lib.rs
index 7cc6a3267d..d18dd943fd 100644
--- a/datadog-sidecar-ffi/src/lib.rs
+++ b/datadog-sidecar-ffi/src/lib.rs
@@ -723,6 +723,30 @@ pub unsafe extern "C" fn ddog_sidecar_session_set_process_tags(
     MaybeError::None
 }
 
+/// Records the default service name for the session. Empty = user-defined
+/// (sidecar emits `svc.user:true`); non-empty = auto-resolved with that name
+/// (sidecar emits `svc.auto:<name>`).
+#[no_mangle]
+#[allow(clippy::missing_safety_doc)]
+pub unsafe extern "C" fn ddog_sidecar_session_set_default_service_name(
+    transport: &mut Box<SidecarTransport>,
+    default_service_name: ffi::CharSlice,
+) -> MaybeError {
+    let source = if default_service_name.is_empty() {
+        datadog_sidecar::service::ServiceNameSource::UserDefined
+    } else {
+        datadog_sidecar::service::ServiceNameSource::AutoResolved(
+            default_service_name.to_utf8_lossy().into_owned(),
+        )
+    };
+    try_c!(blocking::set_session_default_service_name(
+        transport,
+        Some(source),
+    ));
+
+    MaybeError::None
+}
+
 #[repr(C)]
 pub struct TracerHeaderTags<'a> {
     pub lang: ffi::CharSlice<'a>,
diff --git a/datadog-sidecar/src/service/blocking.rs b/datadog-sidecar/src/service/blocking.rs
index 99b84af008..fb7c324d97 100644
--- a/datadog-sidecar/src/service/blocking.rs
+++ b/datadog-sidecar/src/service/blocking.rs
@@ -258,6 +258,14 @@ pub fn set_session_process_tags(
     Ok(())
 }
 
+pub fn set_session_default_service_name(
+    transport: &mut SidecarTransport,
+    service_name_source: Option<crate::service::ServiceNameSource>,
+) -> io::Result<()> {
+    lock_sender(transport)?.set_session_default_service_name(service_name_source);
+    Ok(())
+}
+
 /// Sends a trace as bytes.
 pub fn send_trace_v04_bytes(
     transport: &mut SidecarTransport,
diff --git a/datadog-sidecar/src/service/mod.rs b/datadog-sidecar/src/service/mod.rs
index bc5930fc78..8810c20b44 100644
--- a/datadog-sidecar/src/service/mod.rs
+++ b/datadog-sidecar/src/service/mod.rs
@@ -83,3 +83,9 @@ pub enum SidecarAction {
     AddTelemetryMetricPoint((String, f64, Vec<Tag>)),
     PhpComposerTelemetryFile(PathBuf),
 }
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Serialize)]
+pub enum ServiceNameSource {
+    UserDefined,
+    AutoResolved(String),
+}
diff --git a/datadog-sidecar/src/service/runtime_info.rs b/datadog-sidecar/src/service/runtime_info.rs
index d05de803b3..5f40004049 100644
--- a/datadog-sidecar/src/service/runtime_info.rs
+++ b/datadog-sidecar/src/service/runtime_info.rs
@@ -142,7 +142,7 @@ impl ActiveApplication {
             .expect("Expecting remote config invariants to be set early")
             .clone();
 
-        let process_tags = session.process_tags.lock_or_panic().clone();
+        let process_tags = session.process_tags_with_svc_source();
 
         if *session.remote_config_enabled.lock_or_panic() {
             self.remote_config_guard = Some(
diff --git a/datadog-sidecar/src/service/sender.rs b/datadog-sidecar/src/service/sender.rs
index f3bc672fd0..91b41ee183 100644
--- a/datadog-sidecar/src/service/sender.rs
+++ b/datadog-sidecar/src/service/sender.rs
@@ -35,6 +35,7 @@ use tracing::trace;
 struct SidecarOutbox {
     set_session_config: Option<SidecarInterfaceRequest>,
     set_session_process_tags: Option<SidecarInterfaceRequest>,
+    set_session_default_service_name: Option<SidecarInterfaceRequest>,
     set_universal_service_tags: Option<SidecarInterfaceRequest>,
     set_request_config: Option<SidecarInterfaceRequest>,
     clear_queue_id: Option<SidecarInterfaceRequest>,
@@ -43,10 +44,11 @@ struct SidecarOutbox {
 }
 
 impl SidecarOutbox {
-    fn slots_mut(&mut self) -> [&mut Option<SidecarInterfaceRequest>; 7] {
+    fn slots_mut(&mut self) -> [&mut Option<SidecarInterfaceRequest>; 8] {
         [
             &mut self.set_session_config,
             &mut self.set_session_process_tags,
+            &mut self.set_session_default_service_name,
             &mut self.set_universal_service_tags,
             &mut self.set_request_config,
             &mut self.clear_queue_id,
@@ -122,6 +124,9 @@ fn coalesce(outbox: &mut SidecarOutbox, incoming: SidecarInterfaceRequest) {
         SidecarInterfaceRequest::SetSessionProcessTags { .. } => {
             outbox.set_session_process_tags = Some(incoming);
         }
+        SidecarInterfaceRequest::SetSessionDefaultServiceName { .. } => {
+            outbox.set_session_default_service_name = Some(incoming);
+        }
         SidecarInterfaceRequest::SetUniversalServiceTags { .. } => {
             outbox.set_universal_service_tags = Some(incoming);
         }
@@ -236,6 +241,19 @@ impl SidecarSender {
         self.try_drain_outbox();
     }
 
+    pub fn set_session_default_service_name(
+        &mut self,
+        service_name_source: Option<crate::service::ServiceNameSource>,
+    ) {
+        coalesce(
+            &mut self.outbox,
+            SidecarInterfaceRequest::SetSessionDefaultServiceName {
+                service_name_source,
+            },
+        );
+        self.try_drain_outbox();
+    }
+
     #[allow(clippy::too_many_arguments)]
     pub fn set_universal_service_tags(
         &mut self,
diff --git a/datadog-sidecar/src/service/session_info.rs b/datadog-sidecar/src/service/session_info.rs
index efa0204715..dee6cec678 100644
--- a/datadog-sidecar/src/service/session_info.rs
+++ b/datadog-sidecar/src/service/session_info.rs
@@ -18,7 +18,7 @@ use libdd_common::{tag::Tag, MutexExt};
 use tracing::{debug, error, info, trace, warn};
 
 use crate::service::agent_info::AgentInfoGuard;
-use crate::service::{InstanceId, QueueId, RuntimeInfo};
+use crate::service::{InstanceId, QueueId, RuntimeInfo, ServiceNameSource};
 
 /// `SessionInfo` holds information about a session.
 ///
@@ -45,6 +45,7 @@ pub(crate) struct SessionInfo {
     pub(crate) pid: Arc<AtomicI32>,
     pub(crate) remote_config_enabled: Arc<Mutex<bool>>,
     pub(crate) process_tags: Arc<Mutex<Vec<Tag>>>,
+    pub(crate) service_name_source: Arc<Mutex<Option<ServiceNameSource>>>,
     pub(crate) stats_config: Arc<Mutex<Option<crate::service::stats_flusher::StatsConfig>>>,
 }
 
@@ -130,6 +131,31 @@ impl SessionInfo {
         self.runtimes.lock_or_panic()
     }
 
+    pub(crate) fn process_tags_with_svc_source(&self) -> Vec<Tag> {
+        let mut tags = self.process_tags.lock_or_panic().clone();
+        if let Some(source) = self.service_name_source.lock_or_panic().as_ref() {
+            let (key, value) = match source {
+                ServiceNameSource::UserDefined => ("svc.user", "true".to_string()),
+                ServiceNameSource::AutoResolved(name) => ("svc.auto", name.clone()),
+            };
+            if let Ok(tag) = Tag::new(key, value) {
+                tags.push(tag);
+            }
+        }
+        tags
+    }
+
+    pub(crate) fn refresh_stats_process_tags(&self) {
+        if let Some(stats) = self.stats_config.lock_or_panic().as_mut() {
+            stats.process_tags = self
+                .process_tags_with_svc_source()
+                .iter()
+                .map(|t| t.to_string())
+                .collect::<Vec<_>>()
+                .join(",");
+        }
+    }
+
     pub(crate) fn get_telemetry_config(
         &self,
     ) -> MutexGuard<'_, Option<libdd_telemetry::config::Config>> {
diff --git a/datadog-sidecar/src/service/sidecar_interface.rs b/datadog-sidecar/src/service/sidecar_interface.rs
index ff6313ba36..35406c7bad 100644
--- a/datadog-sidecar/src/service/sidecar_interface.rs
+++ b/datadog-sidecar/src/service/sidecar_interface.rs
@@ -69,6 +69,11 @@ pub trait SidecarInterface {
     /// * `process_tags` - The process tags.
     async fn set_session_process_tags(process_tags: Vec<Tag>);
 
+    /// Records the source of the default service name for the session.
+    async fn set_session_default_service_name(
+        service_name_source: Option<crate::service::ServiceNameSource>,
+    );
+
     /// Removes the application entry for the given queue ID from the instance.
     ///
     /// # Arguments
diff --git a/datadog-sidecar/src/service/sidecar_server.rs b/datadog-sidecar/src/service/sidecar_server.rs
index e4841081a6..45ee68f0ee 100644
--- a/datadog-sidecar/src/service/sidecar_server.rs
+++ b/datadog-sidecar/src/service/sidecar_server.rs
@@ -416,7 +416,7 @@ impl SidecarInterface for ConnectionSidecarHandler {
                 .unwrap_or("unknown-service");
             let env = entry.get().env.as_deref().unwrap_or("none");
 
-            let process_tags = session.process_tags.lock_or_panic().clone();
+            let process_tags = session.process_tags_with_svc_source();
 
             // Pre-compute session config so both the primary and retry get_or_create calls
             // can use it without re-locking the session.
@@ -697,8 +697,8 @@ impl SidecarInterface for ConnectionSidecarHandler {
             } else {
                 config.hostname.clone()
             },
-            process_tags: config
-                .process_tags
+            process_tags: session
+                .process_tags_with_svc_source()
                 .iter()
                 .map(|t| t.to_string())
                 .collect::<Vec<_>>()
@@ -762,6 +762,22 @@ impl SidecarInterface for ConnectionSidecarHandler {
             .unwrap_or_default();
         let session = self.server.get_session(session_id);
         *session.process_tags.lock_or_panic() = process_tags;
+        session.refresh_stats_process_tags();
+    }
+
+    async fn set_session_default_service_name(
+        &self,
+        _peer: PeerCredentials,
+        service_name_source: Option<crate::service::ServiceNameSource>,
+    ) {
+        let session_id = self
+            .session_id
+            .get()
+            .map(|s| s.as_str())
+            .unwrap_or_default();
+        let session = self.server.get_session(session_id);
+        *session.service_name_source.lock_or_panic() = service_name_source;
+        session.refresh_stats_process_tags();
     }
 
     async fn shutdown_runtime(&self, _peer: PeerCredentials, instance_id: InstanceId) {
diff --git a/datadog-sidecar/src/service/telemetry.rs b/datadog-sidecar/src/service/telemetry.rs
index 201f72fb33..3896220f7d 100644
--- a/datadog-sidecar/src/service/telemetry.rs
+++ b/datadog-sidecar/src/service/telemetry.rs
@@ -701,7 +701,7 @@ fn get_telemetry_client(
         return None;
     };
 
-    let process_tags = session.process_tags.lock_or_panic().clone();
+    let process_tags = session.process_tags_with_svc_source();
 
     Some(sidecar.telemetry_clients.get_or_create(
         service_name,