diff --git a/docs/02-setup/04-env-variables.md b/docs/02-setup/04-env-variables.md
index 22a25790..29aa94ec 100644
--- a/docs/02-setup/04-env-variables.md
+++ b/docs/02-setup/04-env-variables.md
@@ -60,6 +60,10 @@ SITES_RULE=Host(`mysite.example.com`)
 SITES_RULE=Host(`a.example.com`) || Host(`b.example.com`)
 ```
 
+> Note: `SITES` currently supplies the host list that goes into the `Host(...)` rules. Once the Traefik v3 transition is completed, the plan is to switch to `SITES_RULE` (full rule expression) and deprecate `SITES` to map the Traefik Rule Syntax.
+
+> Currently the used syntax is pinned to v2 via `--core.defaultRuleSyntax=v2`).
+
 ---
 
 ## Site Configuration
diff --git a/overrides/compose.https.yaml b/overrides/compose.https.yaml
index c9c0f525..13555363 100644
--- a/overrides/compose.https.yaml
+++ b/overrides/compose.https.yaml
@@ -14,6 +14,9 @@ services:
     command:
       - --providers.docker=true
       - --providers.docker.exposedbydefault=false
+      # Keep v2 rule syntax for now
+      # Ensure compatibility with existing labels (will be removed if v3 transition is complete)
+      - --core.defaultRuleSyntax=v2
       - --entrypoints.web.address=:80
       - --entrypoints.web.http.redirections.entrypoint.to=websecure
       - --entrypoints.web.http.redirections.entrypoint.scheme=https
diff --git a/overrides/compose.proxy.yaml b/overrides/compose.proxy.yaml
index feada975..a47b3a7e 100644
--- a/overrides/compose.proxy.yaml
+++ b/overrides/compose.proxy.yaml
@@ -12,6 +12,9 @@ services:
     command:
       - --providers.docker
       - --providers.docker.exposedbydefault=false
+      # Keep v2 rule syntax for now
+      # Ensure compatibility with existing labels (will be removed if v3 transition is complete)
+      - --core.defaultRuleSyntax=v2
       - --entrypoints.web.address=:80
     ports:
       - ${HTTP_PUBLISH_PORT:-80}:80
diff --git a/overrides/compose.traefik-ssl.yaml b/overrides/compose.traefik-ssl.yaml
index 0bdf45fe..2563363c 100644
--- a/overrides/compose.traefik-ssl.yaml
+++ b/overrides/compose.traefik-ssl.yaml
@@ -24,6 +24,9 @@ services:
       - --providers.docker=true
       # Do not expose all Docker services, only the ones explicitly exposed
       - --providers.docker.exposedbydefault=false
+      # Keep v2 rule syntax for now
+      # Ensure compatibility with existing labels (will be removed if v3 transition is complete)
+      - --core.defaultRuleSyntax=v2
       # Create an entrypoint http listening on port 80
       - --entrypoints.http.address=:80
       # Create an entrypoint https listening on port 443
diff --git a/overrides/compose.traefik.yaml b/overrides/compose.traefik.yaml
index 15885363..e36fcd2b 100644
--- a/overrides/compose.traefik.yaml
+++ b/overrides/compose.traefik.yaml
@@ -25,6 +25,9 @@ services:
       - --providers.docker=true
       # Do not expose all Docker services, only the ones explicitly exposed
       - --providers.docker.exposedbydefault=false
+      # Keep v2 rule syntax for now
+      # Ensure compatibility with existing labels (will be removed if v3 transition is complete)
+      - --core.defaultRuleSyntax=v2
       # Create an entrypoint http listening on port 80
       - --entrypoints.http.address=:80
       # Enable the access log, with HTTP requests