diff --git a/README.md b/README.md
index 5853a7568..e21fb4983 100644
--- a/README.md
+++ b/README.md
@@ -281,6 +281,12 @@ candidate models, their harnesses, and the router name sent with each recorded
 decision. Feedback investigations can compare the selection with that original
 menu without querying the router again.
 
+Claude and Codex routing reasons summarize the task profile in plain language, such as
+"This task has a clear target and limited scope." A separate sentence explains when
+model availability requires a higher tier. Custom gateway notices are retained, and
+older or unrecognized responses keep their original wording. Diagnostic records keep
+the displayed reason in `rationale` and the gateway's full explanation in `raw_rationale`.
+
 On Windows, Claude smart routing uses subagent hooks only. If first-prompt routing
 is enabled, ug warns and falls back to subagent routing because the first-prompt
 wrapper requires a Unix terminal.
diff --git a/src/ucode/smart_routing/rationale.py b/src/ucode/smart_routing/rationale.py
new file mode 100644
index 000000000..78cafebad
--- /dev/null
+++ b/src/ucode/smart_routing/rationale.py
@@ -0,0 +1,64 @@
+"""Plain-language explanations of structured task-router decisions."""
+
+_PROFILE_REASONS = (
+    (
+        "localization_burden",
+        "open_search",
+        "This task needs investigation to find what needs attention.",
+    ),
+    ("scope", "cross_cutting", "This task spans several components."),
+    ("environment_burden", "live_external", "This task depends on live systems or data."),
+    ("reasoning_depth", "open_ended", "Solving this task requires exploring possible approaches."),
+    ("verification_strength", "weak", "There is no clear way to check the result of this task."),
+    ("scope", "connected", "This task involves several related components."),
+    ("reasoning_depth", "multi_step", "This task involves several dependent steps."),
+    ("localization_burden", "bounded_search", "This task needs a focused search."),
+)
+
+
+def format_rationale(selection: dict, rationale: str) -> str:
+    """Summarize task_v3 profiles, preserving unfamiliar responses and gateway notices."""
+    params = selection.get("params")
+    if not isinstance(params, dict) or params.get("router_version") != "task_v3":
+        return rationale
+    task_tier, served_tier = params.get("task_tier"), params.get("served_tier")
+    tiers = ("Low", "Medium", "High")
+    if task_tier not in tiers or served_tier not in tiers:
+        return rationale
+    if tiers.index(served_tier) < tiers.index(task_tier):
+        return rationale
+
+    evidence = params.get("evidence_spans")
+    if not isinstance(evidence, list) or len(evidence) != 1 or not isinstance(evidence[0], str):
+        return rationale
+    ending = f" Request: “{evidence[0]}”."
+    if task_tier != served_tier:
+        ending += f" Your configured model availability requires service at {served_tier}."
+    # Only replace the known generated portion; custom gateway notices follow it.
+    _, separator, notice = rationale.partition(ending)
+    if not separator:
+        return rationale
+
+    profile = params.get("task_profile")
+    if params.get("profiler_status") == "unavailable":
+        if task_tier != "High" or served_tier != "High":
+            return rationale
+        reason = "The task could not be assessed, so a high-capability model was selected."
+    elif params.get("profiler_status") == "ok" and isinstance(profile, dict):
+        reason = next(
+            (text for field, value, text in _PROFILE_REASONS if profile.get(field) == value),
+            "",
+        )
+        if (
+            not reason
+            and profile.get("localization_burden") == "explicit_target"
+            and profile.get("scope") == "localized"
+        ):
+            reason = "This task has a clear target and limited scope."
+        if not reason:
+            return rationale
+    else:
+        return rationale
+    if task_tier != served_tier:
+        reason += " A higher-tier model was selected because the requested tier isn't available."
+    return " ".join(part for part in (reason, notice.strip()) if part)
diff --git a/src/ucode/smart_routing/routing.py b/src/ucode/smart_routing/routing.py
index efc352c4d..6286c767d 100644
--- a/src/ucode/smart_routing/routing.py
+++ b/src/ucode/smart_routing/routing.py
@@ -23,6 +23,8 @@
 from pathlib import Path
 from typing import Any
 
+from ucode.smart_routing.rationale import format_rationale
+
 ROUTER_NAME = "task_v3"
 ROUTER_NAME_ENV_VAR = "SMART_ROUTER_NAME"
 ROUTING_PATH = "/ai-gateway/routing/v1/routes:select"
@@ -94,6 +96,7 @@ class RoutingDecision:
     rationale: str = ""
     route_options: tuple[tuple[str, str | None], ...] = ()
     router_name: str = ""
+    raw_rationale: str | None = None
 
     def display_message(
         self,
@@ -262,14 +265,17 @@ def select_route(
     model = resolve(raw_model)
     if model is None:
         return None, f"router selected unsupported model {raw_model!r}"
-    rationale = payload.get("rationale") if isinstance(payload, dict) else None
+    raw_rationale = payload.get("rationale")
+    raw_rationale = raw_rationale if isinstance(raw_rationale, str) else ""
+    rationale = format_rationale(payload["route_selection"][0], raw_rationale)
     return (
         RoutingDecision(
             model=model,
             raw_model=raw_model,
-            rationale=rationale if isinstance(rationale, str) else "",
+            rationale=rationale,
             route_options=offered_routes,
             router_name=router_name,
+            raw_rationale=raw_rationale if rationale != raw_rationale else None,
         ),
         None,
     )
@@ -424,6 +430,9 @@ def write_decision_record(
             # Persisted for diagnosis: an empty value means the gateway returned
             # no rationale (vs. a placement bug in how we surface it).
             "rationale": decision.rationale,
+            "raw_rationale": decision.raw_rationale
+            if decision.raw_rationale is not None
+            else decision.rationale,
             "at": time.time(),
         },
     )
diff --git a/tests/test_routing_rationale.py b/tests/test_routing_rationale.py
new file mode 100644
index 000000000..03b4add21
--- /dev/null
+++ b/tests/test_routing_rationale.py
@@ -0,0 +1,26 @@
+from ucode.smart_routing.rationale import format_rationale
+
+
+def test_plain_language_reason():
+    selection = {
+        "params": {
+            "router_version": "task_v3",
+            "task_tier": "Low",
+            "served_tier": "Low",
+            "profiler_status": "ok",
+            "evidence_spans": ["Inspect the parser."],
+            "task_profile": {"localization_burden": "explicit_target", "scope": "localized"},
+        }
+    }
+    rationale = (
+        "Routed to Low because its task-only profile is low: "
+        "an explicit target, localized scope, direct reasoning. Request: “Inspect the parser.”."
+    )
+    assert (
+        format_rationale(selection, rationale) == "This task has a clear target and limited scope."
+    )
+
+
+def test_unknown_response_is_preserved():
+    rationale = "A custom routing explanation."
+    assert format_rationale({}, rationale) == rationale