diff --git a/changelog.d/fixes/11557-shed-redundant-routing-segments.md b/changelog.d/fixes/11557-shed-redundant-routing-segments.md
new file mode 100644
index 0000000000..7a4b3228b1
--- /dev/null
+++ b/changelog.d/fixes/11557-shed-redundant-routing-segments.md
@@ -0,0 +1 @@
+- fix(chat): shed any of the matched provider-node's routing identifiers (public prefix or internal id) before model lookup, so composites like `<connId>/<connId>/<model>` no longer reach upstream verbatim (#11557)
diff --git a/src/sse/services/model.ts b/src/sse/services/model.ts
index c7cbfef9b5..aa317dcb96 100644
--- a/src/sse/services/model.ts
+++ b/src/sse/services/model.ts
@@ -388,17 +388,34 @@ async function lookupModelMeta(
 /**
  * When a custom provider node is matched by its raw internal `node.id` (e.g. a combo
  * step addressing `<connId>/...` — see #2778), `parsed.model` was never split on the
- * node's own `prefix`, unlike the alias-addressing path where `parseModel` already
- * strips it. If the caller naively concatenates `owned_by` (the node's prefix, as
- * listed by /api/models) with the raw model id, the resulting model string carries a
- * redundant leading `${node.prefix}/` segment that the upstream provider does not
- * recognize, causing a 400. Strip it so `<connId>/<prefix>/<rawModelId>` normalizes to
- * the same `<rawModelId>` the bare alias form resolves to (#6772).
+ * node's own identifiers, unlike the alias-addressing path where `parseModel` already
+ * strips the prefix. If the caller naively concatenates routing segments with the raw
+ * model id, the resulting model string carries redundant leading segments that the
+ * upstream provider does not recognize, causing deterministic 404s (retried).
+ *
+ * Observed in production traffic: `<connId>/<connId>/<model>` — requests addressed
+ * by the node's internal id (#2778) left a second `<connId>/` segment in parsed.model
+ * that the historical strip (prefix alone, #6772) never saw, and the composite went
+ * upstream verbatim. We now shed ANY of the matched node's routing identifiers (prefix AND internal id), repeatedly, until stable.
+ * A legitimate namespace different from these identifiers is untouched (#493);
+ * an operator naming their prefix identically to one of their catalog namespaces
+ * sees that namespace shed — accepted limitation, precedent #6772.
  */
-function stripRedundantNodePrefix(model: string, nodePrefix: unknown): string {
-  if (typeof nodePrefix !== "string" || !nodePrefix) return model;
-  const redundant = `${nodePrefix}/`;
-  return model.startsWith(redundant) ? model.slice(redundant.length) : model;
+function stripRedundantNodeRoutingSegments(model: string, routingIds: unknown[]): string {
+  let out = model;
+  let changed = true;
+  while (changed) {
+    changed = false;
+    for (const seg of routingIds) {
+      if (typeof seg !== "string" || !seg) continue;
+      const redundant = `${seg}/`;
+      if (out.startsWith(redundant)) {
+        out = out.slice(redundant.length);
+        changed = true;
+      }
+    }
+  }
+  return out;
 }
 
 /**
@@ -457,10 +474,10 @@ export async function getModelInfo(modelStr) {
         (node) => node.prefix === prefixToCheck || node.id === prefixToCheck
       );
       if (matchedOpenAI) {
-        const normalizedModel = stripRedundantNodePrefix(
-          parsed.model as string,
-          matchedOpenAI.prefix
-        );
+        const normalizedModel = stripRedundantNodeRoutingSegments(parsed.model as string, [
+          matchedOpenAI.prefix,
+          matchedOpenAI.id,
+        ]);
         const { modelId, metadata } = await lookupModelMeta(
           matchedOpenAI.id as string,
           normalizedModel
@@ -479,10 +496,10 @@ export async function getModelInfo(modelStr) {
         (node) => node.prefix === prefixToCheck || node.id === prefixToCheck
       );
       if (matchedAnthropic) {
-        const normalizedModel = stripRedundantNodePrefix(
-          parsed.model as string,
-          matchedAnthropic.prefix
-        );
+        const normalizedModel = stripRedundantNodeRoutingSegments(parsed.model as string, [
+          matchedAnthropic.prefix,
+          matchedAnthropic.id,
+        ]);
         const { modelId, metadata } = await lookupModelMeta(
           matchedAnthropic.id as string,
           normalizedModel
diff --git a/tests/unit/model-connid-prefix-normalization-6772.test.ts b/tests/unit/model-connid-prefix-normalization-6772.test.ts
index 430aa1a7c0..c7b6fca7b4 100644
--- a/tests/unit/model-connid-prefix-normalization-6772.test.ts
+++ b/tests/unit/model-connid-prefix-normalization-6772.test.ts
@@ -84,3 +84,98 @@ test("#6772 RED: `<connId>/<prefix>/<rawModelId>` (naive owned_by+id concat) mus
       `"${RAW_MODEL_ID}" — got "${info.model}" instead (double-namespaced, will 400 upstream)`
   );
 });
+
+// ── shedding redundant routing segments (node prefix AND internal id) ──
+
+const AC_CONN_ID = "anthropic-compatible-a1111111-probeshed";
+const AC_PREFIX = "acustpfx";
+
+test.before(async () => {
+  await providersDb.createProviderNode({
+    id: AC_CONN_ID,
+    type: "anthropic-compatible",
+    name: "probe shed",
+    prefix: AC_PREFIX,
+    baseUrl: "https://proxy.example.com",
+    chatPath: "/v1/messages",
+    modelsPath: "/v1/models",
+  });
+  await modelsDb.addCustomModel(
+    AC_CONN_ID,
+    RAW_MODEL_ID,
+    "vova gpt-5.5",
+    "manual",
+    "chat-completions",
+    ["chat"]
+  );
+});
+
+test("shed measured production-log shape: `<connId>/<connId>/<bare>` sheds to `<bare>`", async () => {
+  const info = (await getModelInfo(`${CONN_ID}/${CONN_ID}/gpt-oss-20b`)) as {
+    provider?: string;
+    model?: string;
+  };
+  assert.equal(info.provider, CONN_ID);
+  assert.equal(info.model, "gpt-oss-20b", `got "${info.model}"`);
+});
+
+test("shed full logged composite: double connId + namespace keeps the namespace after shed", async () => {
+  // Real production log shape: `<connId>/<connId>/openai/gpt-oss-20b:free`.
+  // Shedding removes the matched node's OWN identifiers only; the `openai/`
+  // namespace is out of scope — this test pins that exact promise.
+  const info = (await getModelInfo(`${CONN_ID}/${CONN_ID}/openai/gpt-oss-20b:free`)) as {
+    provider?: string;
+    model?: string;
+  };
+  assert.equal(info.provider, CONN_ID);
+  assert.equal(info.model, "openai/gpt-oss-20b:free", `got "${info.model}"`);
+});
+
+test("shed mixed addressing: `<prefix>/<connId>/<raw>` sheds to `<raw>`", async () => {
+  const info = (await getModelInfo(`${PREFIX}/${CONN_ID}/${RAW_MODEL_ID}`)) as {
+    provider?: string;
+    model?: string;
+  };
+  assert.equal(info.provider, CONN_ID);
+  assert.equal(info.model, RAW_MODEL_ID, `got "${info.model}"`);
+});
+
+test("shed #493 guard: legitimate namespace distinct from the node's identifiers stays intact", async () => {
+  const info = (await getModelInfo(`${CONN_ID}/zai-org/GLM-5-FP8`)) as {
+    provider?: string;
+    model?: string;
+  };
+  assert.equal(info.provider, CONN_ID);
+  assert.equal(info.model, "zai-org/GLM-5-FP8", `got "${info.model}"`);
+});
+
+test("shed SYNTHETIC triple stack: `<connId>/<prefix>/<connId>/<raw>` sheds to `<raw>`", async () => {
+  const info = (await getModelInfo(`${CONN_ID}/${PREFIX}/${CONN_ID}/${RAW_MODEL_ID}`)) as {
+    provider?: string;
+    model?: string;
+  };
+  assert.equal(info.provider, CONN_ID);
+  assert.equal(info.model, RAW_MODEL_ID, `got "${info.model}"`);
+});
+
+test("shed accepted limitation (#6772 precedent): operator prefix equal to a catalog namespace is shed", async () => {
+  // An operator naming their prefix like a real upstream namespace sees that
+  // namespace shed — indistinguishable without querying the catalog.
+  // DOCUMENTARY LOCK: same input as the "bare alias form" baseline above — no
+  // new behavioral coverage; pins the accepted limitation as shedding, not refusal.
+  const info = (await getModelInfo(`${PREFIX}/${RAW_MODEL_ID}`)) as {
+    provider?: string;
+    model?: string;
+  };
+  assert.equal(info.provider, CONN_ID);
+  assert.equal(info.model, RAW_MODEL_ID);
+});
+
+test("shed anthropic-compatible parity: `<acConnId>/<acPrefix>/<raw>` sheds to `<raw>`", async () => {
+  const info = (await getModelInfo(`${AC_CONN_ID}/${AC_PREFIX}/${RAW_MODEL_ID}`)) as {
+    provider?: string;
+    model?: string;
+  };
+  assert.equal(info.provider, AC_CONN_ID);
+  assert.equal(info.model, RAW_MODEL_ID, `got "${info.model}"`);
+});