diff --git a/platform/backend/src/routes/internal-mcp-catalog.env.test.ts b/platform/backend/src/routes/internal-mcp-catalog.env.test.ts
index b2f680bbf0..d2fe85def6 100644
--- a/platform/backend/src/routes/internal-mcp-catalog.env.test.ts
+++ b/platform/backend/src/routes/internal-mcp-catalog.env.test.ts
@@ -701,6 +701,77 @@ spec:
     });
   });
 
+  // =========================================================================
+  // 4. AUTH METHOD SWITCHING
+  // =========================================================================
+  describe("AUTH METHOD SWITCHING", () => {
+    test("4.1 switches from OAuth to Bearer — clears oauthConfig", async () => {
+      // Create catalog with OAuth config
+      const catalog = await InternalMcpCatalogModel.create({
+        name: "test-oauth-to-bearer",
+        serverType: "remote",
+        serverUrl: "https://example.com/mcp",
+        oauthConfig: {
+          name: "test-oauth-to-bearer",
+          server_url: "https://example.com/mcp",
+          client_id: "test-client-id",
+          redirect_uris: ["https://localhost/callback"],
+          scopes: ["read", "write"],
+          default_scopes: ["read", "write"],
+          supports_resource_metadata: true,
+        },
+      });
+
+      expect(catalog.oauthConfig).not.toBeNull();
+
+      // Switch to Bearer by setting oauthConfig to null and providing userConfig
+      const updated = await InternalMcpCatalogModel.update(catalog.id, {
+        oauthConfig: null,
+        userConfig: {
+          access_token: {
+            type: "string",
+            title: "Access Token",
+            description: "Bearer token for authentication",
+            required: true,
+            sensitive: true,
+          },
+        },
+      });
+
+      expect(updated?.oauthConfig).toBeNull();
+      expect(updated?.userConfig).toHaveProperty("access_token");
+    });
+
+    test("4.2 switches from OAuth to no auth — clears oauthConfig and userConfig", async () => {
+      // Create catalog with OAuth config
+      const catalog = await InternalMcpCatalogModel.create({
+        name: "test-oauth-to-none",
+        serverType: "remote",
+        serverUrl: "https://example.com/mcp",
+        oauthConfig: {
+          name: "test-oauth-to-none",
+          server_url: "https://example.com/mcp",
+          client_id: "test-client-id",
+          redirect_uris: ["https://localhost/callback"],
+          scopes: ["read", "write"],
+          default_scopes: ["read", "write"],
+          supports_resource_metadata: true,
+        },
+      });
+
+      expect(catalog.oauthConfig).not.toBeNull();
+
+      // Switch to no auth
+      const updated = await InternalMcpCatalogModel.update(catalog.id, {
+        oauthConfig: null,
+        userConfig: {},
+      });
+
+      expect(updated?.oauthConfig).toBeNull();
+      expect(updated?.userConfig).toEqual({});
+    });
+  });
+
   // =========================================================================
   // Edge Cases
   // =========================================================================
diff --git a/platform/backend/src/routes/internal-mcp-catalog.ts b/platform/backend/src/routes/internal-mcp-catalog.ts
index 49cbbc7af6..5b4363ca58 100644
--- a/platform/backend/src/routes/internal-mcp-catalog.ts
+++ b/platform/backend/src/routes/internal-mcp-catalog.ts
@@ -395,6 +395,12 @@ const internalMcpCatalogRoutes: FastifyPluginAsyncZod = async (fastify) => {
         delete restBody.oauthConfig.client_secret;
       }
 
+      // Handle switching away from OAuth: clean up old client secret
+      if (restBody.oauthConfig === null && originalCatalogItem.clientSecretId) {
+        await secretManager().deleteSecret(originalCatalogItem.clientSecretId);
+        restBody.clientSecretId = null;
+      }
+
       // Handle local config secrets - either via Readonly Vault or direct values
       if (localConfigVaultPath && localConfigVaultKey) {
         // Readonly Vault flow for local config secrets
diff --git a/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.test.ts b/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.test.ts
index 8e465ac19e..882f657b97 100644
--- a/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.test.ts
+++ b/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.test.ts
@@ -1,5 +1,9 @@
+import type { McpCatalogFormValues } from "./mcp-catalog-form.types";
 import { formSchema } from "./mcp-catalog-form.types";
-import { stripEnvVarQuotes } from "./mcp-catalog-form.utils";
+import {
+  stripEnvVarQuotes,
+  transformFormToApiData,
+} from "./mcp-catalog-form.utils";
 
 describe("stripEnvVarQuotes", () => {
   describe("real-world environment variable examples", () => {
@@ -290,3 +294,62 @@ describe("formSchema", () => {
     });
   });
 });
+
+describe("transformFormToApiData", () => {
+  const baseFormValues: McpCatalogFormValues = {
+    name: "test-server",
+    serverType: "remote",
+    serverUrl: "https://example.com/mcp",
+    authMethod: "none",
+    oauthConfig: undefined,
+  };
+
+  it("oauthConfig is null when authMethod is bearer", () => {
+    const result = transformFormToApiData({
+      ...baseFormValues,
+      authMethod: "bearer",
+    });
+    expect(result.oauthConfig).toBeNull();
+  });
+
+  it("oauthConfig is null when authMethod is raw_token", () => {
+    const result = transformFormToApiData({
+      ...baseFormValues,
+      authMethod: "raw_token",
+    });
+    expect(result.oauthConfig).toBeNull();
+  });
+
+  it("oauthConfig is null when authMethod is none", () => {
+    const result = transformFormToApiData({
+      ...baseFormValues,
+      authMethod: "none",
+    });
+    expect(result.oauthConfig).toBeNull();
+  });
+
+  it("oauthConfig is set when authMethod is oauth", () => {
+    const result = transformFormToApiData({
+      ...baseFormValues,
+      authMethod: "oauth",
+      oauthConfig: {
+        client_id: "test-id",
+        client_secret: "test-secret",
+        redirect_uris: "https://localhost/callback",
+        scopes: "read,write",
+        supports_resource_metadata: true,
+      },
+    });
+    expect(result.oauthConfig).not.toBeNull();
+    expect(result.oauthConfig?.client_id).toBe("test-id");
+  });
+
+  it("null oauthConfig survives JSON serialization", () => {
+    const result = transformFormToApiData({
+      ...baseFormValues,
+      authMethod: "bearer",
+    });
+    const roundTripped = JSON.parse(JSON.stringify(result));
+    expect(roundTripped.oauthConfig).toBeNull();
+  });
+});
diff --git a/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.utils.ts b/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.utils.ts
index ba45b00a65..49f2b32636 100644
--- a/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.utils.ts
+++ b/platform/frontend/src/app/mcp-catalog/_parts/mcp-catalog-form.utils.ts
@@ -116,7 +116,7 @@ export function transformFormToApiData(
       },
     };
     // Clear oauthConfig when using Bearer Token
-    data.oauthConfig = undefined;
+    data.oauthConfig = null;
   } else if (values.authMethod === "raw_token") {
     // Handle Token (no prefix) configuration
     data.userConfig = {
@@ -129,11 +129,11 @@ export function transformFormToApiData(
       },
     };
     // Clear oauthConfig when using Token
-    data.oauthConfig = undefined;
+    data.oauthConfig = null;
   } else {
     // No authentication - clear both configs
     data.userConfig = {};
-    data.oauthConfig = undefined;
+    data.oauthConfig = null;
   }
 
   // Handle labels