diff --git a/src/proxy.ts b/src/proxy.ts
index 82c503b..7d5e303 100644
--- a/src/proxy.ts
+++ b/src/proxy.ts
@@ -287,6 +287,10 @@ const PROVIDER_ERROR_PATTERNS = [
   /billing/i,
   /insufficient.*balance/i,
   /credits/i,
+  /payment required/i,
+  /x402[_-]?payment[_-]?failed/i,
+  /merchant_status\"?\s*:\s*402/i,
+  /endpoint requires x402 payment/i,
   /quota.*exceeded/i,
   /rate.*limit/i,
   /model.*unavailable/i,
@@ -1379,7 +1383,7 @@ async function proxyRequest(
           );
           const existingSession = sessionId ? sessionStore.getSession(sessionId) : undefined;
 
-          if (existingSession) {
+          if (existingSession && existingSession.routingProfile === routingProfile) {
             // Use the session's pinned model instead of re-routing
             console.log(
               `[ClawRouter] Session ${sessionId?.slice(0, 8)}... using pinned model: ${existingSession.model}`,
@@ -1389,6 +1393,13 @@ async function proxyRequest(
             bodyModified = true;
             sessionStore.touchSession(sessionId!);
           } else {
+            if (existingSession && sessionId) {
+              console.log(
+                `[ClawRouter] Session ${sessionId.slice(0, 8)}... profile changed (${existingSession.routingProfile ?? "unknown"} -> ${routingProfile}), re-routing`,
+              );
+              sessionStore.clearSession(sessionId);
+            }
+
             // No session or expired - route normally
             // Extract prompt from messages
             type ChatMessage = { role: string; content: string };
@@ -1431,7 +1442,12 @@ async function proxyRequest(
 
             // Pin this model to the session for future requests
             if (sessionId) {
-              sessionStore.setSession(sessionId, routingDecision.model, routingDecision.tier);
+              sessionStore.setSession(
+                sessionId,
+                routingDecision.model,
+                routingDecision.tier,
+                routingProfile ?? undefined,
+              );
               console.log(
                 `[ClawRouter] Session ${sessionId.slice(0, 8)}... pinned to model: ${routingDecision.model}`,
               );
diff --git a/src/session.ts b/src/session.ts
index 277fe51..95c63bd 100644
--- a/src/session.ts
+++ b/src/session.ts
@@ -9,6 +9,7 @@
 export type SessionEntry = {
   model: string;
   tier: string;
+  routingProfile?: "free" | "eco" | "auto" | "premium";
   createdAt: number;
   lastUsedAt: number;
   requestCount: number;
@@ -72,7 +73,12 @@ export class SessionStore {
   /**
    * Pin a model to a session.
    */
-  setSession(sessionId: string, model: string, tier: string): void {
+  setSession(
+    sessionId: string,
+    model: string,
+    tier: string,
+    routingProfile?: "free" | "eco" | "auto" | "premium",
+  ): void {
     if (!this.config.enabled || !sessionId) {
       return;
     }
@@ -88,10 +94,12 @@ export class SessionStore {
         existing.model = model;
         existing.tier = tier;
       }
+      existing.routingProfile = routingProfile;
     } else {
       this.sessions.set(sessionId, {
         model,
         tier,
+        routingProfile,
         createdAt: now,
         lastUsedAt: now,
         requestCount: 1,
diff --git a/test/premium-compat.ts b/test/premium-compat.ts
new file mode 100644
index 0000000..09d6df5
--- /dev/null
+++ b/test/premium-compat.ts
@@ -0,0 +1,180 @@
+/**
+ * Regression tests for premium payment compatibility issues:
+ * 1) x402 wrapped payment failures should be treated as provider errors and fallback.
+ * 2) Session pinning should not override routing profile switches (premium -> eco).
+ *
+ * Usage:
+ *   bun run test/premium-compat.ts
+ */
+
+import { createServer, type IncomingMessage, type ServerResponse } from "node:http";
+import type { AddressInfo } from "node:net";
+import { startProxy } from "../src/proxy.js";
+
+type MockState = {
+  modelCalls: string[];
+  wrappedPaymentFailureModels: Set<string>;
+};
+
+async function startMockApi(state: MockState): Promise<{ port: number; close: () => Promise<void> }> {
+  const server = createServer(async (req: IncomingMessage, res: ServerResponse) => {
+    const chunks: Buffer[] = [];
+    for await (const chunk of req) {
+      chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk));
+    }
+
+    try {
+      const body = JSON.parse(Buffer.concat(chunks).toString()) as { model?: string };
+      const model = body.model || "unknown";
+      state.modelCalls.push(model);
+
+      if (state.wrappedPaymentFailureModels.has(model)) {
+        // Real-world shape observed in logs: 400 with embedded x402 payment failure details.
+        res.writeHead(400, { "Content-Type": "application/json" });
+        res.end(
+          JSON.stringify({
+            error:
+              'Payment required: {"error":"x402_payment_failed","merchant_status":402,"merchant_body":"{\\"error\\":\\"Payment Required\\",\\"message\\":\\"This endpoint requires x402 payment\\"}"}',
+          }),
+        );
+        return;
+      }
+
+      res.writeHead(200, { "Content-Type": "application/json" });
+      res.end(
+        JSON.stringify({
+          id: "chatcmpl-test",
+          object: "chat.completion",
+          created: Date.now(),
+          model,
+          choices: [{ index: 0, message: { role: "assistant", content: `ok:${model}` } }],
+          usage: { prompt_tokens: 10, completion_tokens: 10, total_tokens: 20 },
+        }),
+      );
+    } catch {
+      res.writeHead(400, { "Content-Type": "application/json" });
+      res.end(JSON.stringify({ error: "Invalid request body" }));
+    }
+  });
+
+  const port = 25000 + Math.floor(Math.random() * 1000);
+  await new Promise<void>((resolve, reject) => {
+    server.once("error", reject);
+    server.listen(port, "127.0.0.1", () => {
+      server.removeListener("error", reject);
+      resolve();
+    });
+  });
+
+  return {
+    port,
+    close: () => new Promise<void>((resolve) => server.close(() => resolve())),
+  };
+}
+
+let passed = 0;
+let failed = 0;
+function assert(condition: boolean, msg: string): void {
+  if (condition) {
+    console.log(`  ✓ ${msg}`);
+    passed++;
+  } else {
+    console.error(`  ✗ FAIL: ${msg}`);
+    failed++;
+  }
+}
+
+async function run(): Promise<void> {
+  console.log("\n═══ Premium Compatibility Tests ═══\n");
+
+  const state: MockState = {
+    modelCalls: [],
+    wrappedPaymentFailureModels: new Set(),
+  };
+
+  const mockApi = await startMockApi(state);
+  const proxyPort = 26000 + Math.floor(Math.random() * 1000);
+  const proxy = await startProxy({
+    walletKey: `0x${"1".repeat(64)}`,
+    apiBase: `http://127.0.0.1:${mockApi.port}`,
+    port: proxyPort,
+    skipBalanceCheck: true,
+    sessionConfig: { enabled: true, headerName: "x-session-id" },
+  });
+
+  // Test 1: wrapped x402 payment failure must fallback to free model.
+  {
+    console.log("--- Test 1: wrapped x402 failure triggers fallback ---");
+    state.modelCalls.length = 0;
+    state.wrappedPaymentFailureModels = new Set(["xai/grok-code-fast-1"]);
+
+    const res = await fetch(`${proxy.baseUrl}/v1/chat/completions`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({
+        model: "xai/grok-code-fast-1",
+        messages: [{ role: "user", content: "hello" }],
+        max_tokens: 128,
+      }),
+    });
+
+    assert(res.ok, `request succeeds via fallback: ${res.status}`);
+    assert(
+      state.modelCalls.join(",") === "xai/grok-code-fast-1,nvidia/gpt-oss-120b",
+      `fallback chain used expected models: ${state.modelCalls.join(", ")}`,
+    );
+  }
+
+  // Test 2: session pin should not cross routing profiles.
+  {
+    console.log("--- Test 2: session profile switch re-routes ---");
+    state.modelCalls.length = 0;
+    state.wrappedPaymentFailureModels = new Set();
+    const sessionId = `sess-${Date.now()}`;
+    const prompt = "Prove step by step that sqrt(2) is irrational.";
+
+    const premiumRes = await fetch(`${proxy.baseUrl}/v1/chat/completions`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json", "x-session-id": sessionId },
+      body: JSON.stringify({
+        model: "premium",
+        messages: [{ role: "user", content: prompt }],
+        max_tokens: 256,
+      }),
+    });
+    assert(premiumRes.ok, `premium request ok: ${premiumRes.status}`);
+
+    const ecoRes = await fetch(`${proxy.baseUrl}/v1/chat/completions`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json", "x-session-id": sessionId },
+      body: JSON.stringify({
+        model: "eco",
+        // Keep tier intent but alter body to avoid request dedup cache hits.
+        messages: [{ role: "user", content: `${prompt} Give a shorter version.` }],
+        max_tokens: 256,
+      }),
+    });
+    assert(ecoRes.ok, `eco request ok: ${ecoRes.status}`);
+
+    const firstModel = state.modelCalls[0];
+    const secondModel = state.modelCalls[1];
+    assert(!!firstModel && !!secondModel, `captured two model calls: ${state.modelCalls.join(", ")}`);
+    assert(
+      secondModel !== "anthropic/claude-sonnet-4",
+      `eco request should not reuse premium pinned model: ${secondModel}`,
+    );
+  }
+
+  await proxy.close();
+  await mockApi.close();
+
+  console.log("\n═══════════════════════════════════");
+  console.log(`  ${passed} passed, ${failed} failed`);
+  console.log("═══════════════════════════════════\n");
+  process.exit(failed > 0 ? 1 : 0);
+}
+
+run().catch((err) => {
+  console.error("Test failed:", err);
+  process.exit(1);
+});