diff --git a/packages/mcp-core/src/api-client/client.test.ts b/packages/mcp-core/src/api-client/client.test.ts
index 63d21b7cd..ce7052fc0 100644
--- a/packages/mcp-core/src/api-client/client.test.ts
+++ b/packages/mcp-core/src/api-client/client.test.ts
@@ -10,6 +10,19 @@ import { parseSentryUrl } from "../internal/url-helpers";
 import { SentryApiService } from "./client";
 import { ApiNotFoundError, ApiPermissionError, ApiServerError } from "./errors";
 
+// Many tests in this file replace `globalThis.fetch` directly. Snapshot and
+// restore it around every test so a mock never leaks into later tests that
+// rely on MSW interception.
+let savedFetch: typeof globalThis.fetch;
+
+beforeEach(() => {
+  savedFetch = globalThis.fetch;
+});
+
+afterEach(() => {
+  globalThis.fetch = savedFetch;
+});
+
 describe("API bearer token validation", () => {
   it("removes edge padding before sending a request", async () => {
     let authorization: string | null = null;
@@ -2412,6 +2425,30 @@ describe("API query builders", () => {
       expect(params.getAll("environment")).toEqual(["production", "staging"]);
       expect(requestOptions?.method).toBeUndefined();
     });
+
+    it("returns null when the validate endpoint is unavailable (404)", async () => {
+      const apiService = new SentryApiService({
+        host: "sentry.example.com",
+        accessToken: "test-token",
+      });
+
+      mswServer.use(
+        http.get(
+          "https://sentry.example.com/api/0/organizations/test-org/events/validate/",
+          () => HttpResponse.json({ detail: "Not Found" }, { status: 404 }),
+        ),
+      );
+
+      const result = await apiService.validateEvents({
+        organizationSlug: "test-org",
+        dataset: "spans",
+        fields: ["span.duration"],
+        query: "",
+        orderby: ["-span.duration"],
+      });
+
+      expect(result).toBeNull();
+    });
   });
 
   describe("Web URL builders", () => {
diff --git a/packages/mcp-core/src/api-client/client.ts b/packages/mcp-core/src/api-client/client.ts
index 40590529b..47989e95a 100644
--- a/packages/mcp-core/src/api-client/client.ts
+++ b/packages/mcp-core/src/api-client/client.ts
@@ -3875,7 +3875,7 @@ export class SentryApiService {
       end?: string;
     },
     opts?: RequestOptions,
-  ): Promise<EventsValidationResult> {
+  ): Promise<EventsValidationResult | null> {
     const queryParams = new URLSearchParams();
     queryParams.set("dataset", normalizeEventsDataset(dataset));
     if (project) {
@@ -3900,12 +3900,20 @@ export class SentryApiService {
       queryParams.append("orderby", value);
     }
 
+    // The events validation endpoint was added to Sentry in mid-2026 and is
+    // absent on older deployments (notably self-hosted instances before that
+    // release). A 404 therefore means "validation is not supported here"
+    // rather than a bad request, so return `null` and let callers skip the
+    // validation gate instead of failing the whole search.
     const response = await this.request(
       apiPath`/organizations/${organizationSlug}/events/validate/` +
         `?${queryParams.toString()}`,
       undefined,
-      { ...opts, allowStatuses: [400] },
+      { ...opts, allowStatuses: [400, 404] },
     );
+    if (response.status === 404) {
+      return null;
+    }
     const body = await this.parseJsonResponse(response);
     return EventsValidationResponseSchema.parse(body);
   }
diff --git a/packages/mcp-core/src/tools/catalog/search-events.test.ts b/packages/mcp-core/src/tools/catalog/search-events.test.ts
index ab030f013..50f4eca69 100644
--- a/packages/mcp-core/src/tools/catalog/search-events.test.ts
+++ b/packages/mcp-core/src/tools/catalog/search-events.test.ts
@@ -2951,6 +2951,75 @@ describe("search_events", () => {
     expect(result).toContain("span1");
   });
 
+  it("runs the search when the validate endpoint is unavailable (404)", async () => {
+    let eventsRequestUrl: URL | undefined;
+
+    mockGenerateText.mockResolvedValueOnce(
+      mockAIResponse(
+        "errors",
+        "level:error",
+        ["issue", "title", "timestamp"],
+        undefined,
+        "-timestamp",
+        { statsPeriod: "24h" },
+      ),
+    );
+
+    // Simulate an older/self-hosted Sentry that does not expose the
+    // `/events/validate/` endpoint.
+    mswServer.use(
+      http.get(
+        "https://sentry.io/api/0/organizations/test-org/events/validate/",
+        () => HttpResponse.json({ detail: "Not Found" }, { status: 404 }),
+      ),
+      http.get(
+        "https://sentry.io/api/0/organizations/test-org/events/",
+        ({ request }) => {
+          eventsRequestUrl = new URL(request.url);
+          return HttpResponse.json({
+            data: [
+              {
+                id: "issue1",
+                title: "Database Error",
+                level: "error",
+                timestamp: "2024-01-15T10:30:00Z",
+              },
+            ],
+          });
+        },
+      ),
+    );
+
+    const result = await searchEvents.handler(
+      {
+        organizationSlug: "test-org",
+        regionUrl: null,
+        projectSlug: null,
+        dataset: "errors",
+        query: "level:error",
+        fields: null,
+        sort: null,
+        period: "24h",
+        limit: 10,
+        includeExplanation: false,
+      },
+      {
+        constraints: {
+          organizationSlug: null,
+          regionUrl: null,
+          projectSlug: null,
+        },
+        accessToken: "test-token",
+        userId: "1",
+      },
+    );
+
+    // Validation is skipped, so the search still executes and returns data.
+    expect(eventsRequestUrl).toBeDefined();
+    expect(eventsRequestUrl!.searchParams.get("dataset")).toBe("errors");
+    expect(result).toContain("Database Error");
+  });
+
   it("fails complete structured requests honestly without an external repair loop", async () => {
     let validateCalls = 0;
 
diff --git a/packages/mcp-core/src/tools/support/search-events/search.ts b/packages/mcp-core/src/tools/support/search-events/search.ts
index 508dd4513..157dfb17d 100644
--- a/packages/mcp-core/src/tools/support/search-events/search.ts
+++ b/packages/mcp-core/src/tools/support/search-events/search.ts
@@ -1000,18 +1000,29 @@ export async function runSearchEvents(
     environment: environment ?? undefined,
     ...timeParams,
   });
-  recordEventsSearchValidationTelemetry({
-    attempt: 0,
-    validation: lastValidation,
-  });
 
-  if (!lastValidation.valid) {
-    const formatted = formatEventsValidationResults(lastValidation);
-    throw new UserInputError(
-      formatted
-        ? `Search validation failed:\n${formatted}`
-        : "Search validation failed.",
+  // `null` means the target deployment does not expose the validation
+  // endpoint (e.g. older self-hosted Sentry). Skip the gate and run the
+  // search directly instead of failing with a misleading 404.
+  if (lastValidation === null) {
+    getActiveSpan()?.setAttribute(
+      "app.search_events.validation.unsupported",
+      true,
     );
+  } else {
+    recordEventsSearchValidationTelemetry({
+      attempt: 0,
+      validation: lastValidation,
+    });
+
+    if (!lastValidation.valid) {
+      const formatted = formatEventsValidationResults(lastValidation);
+      throw new UserInputError(
+        formatted
+          ? `Search validation failed:\n${formatted}`
+          : "Search validation failed.",
+      );
+    }
   }
 
   const finalRequestFields = buildRequestFields(dataset, fields);
diff --git a/packages/mcp-core/src/tools/support/search-events/utils.ts b/packages/mcp-core/src/tools/support/search-events/utils.ts
index d2753b58e..1c421d397 100644
--- a/packages/mcp-core/src/tools/support/search-events/utils.ts
+++ b/packages/mcp-core/src/tools/support/search-events/utils.ts
@@ -884,6 +884,14 @@ export function recordEventsSearchValidationTelemetry({
   }
 }
 
+/**
+ * Validate a candidate events search against Sentry's validation endpoint.
+ *
+ * Returns `null` when the target deployment does not expose the
+ * `/events/validate/` endpoint (e.g. older self-hosted Sentry instances). A
+ * `null` result means validation is unavailable and callers should proceed
+ * with the search rather than treating it as a failure.
+ */
 export async function validateEventsSearch(
   apiService: SentryApiService,
   {
@@ -909,7 +917,7 @@ export async function validateEventsSearch(
     start?: string;
     end?: string;
   },
-): Promise<EventsValidationResult> {
+): Promise<EventsValidationResult | null> {
   return apiService.validateEvents({
     organizationSlug,
     dataset,
@@ -963,6 +971,11 @@ export async function assertEventsSearchIsValid(
     end,
   });
 
+  // `null` means the deployment does not support validation; skip the gate.
+  if (validationResults === null) {
+    return;
+  }
+
   if (!validationResults.valid) {
     const formatted = formatEventsValidationResults(validationResults);
     throw new UserInputError(
@@ -1246,6 +1259,16 @@ export function createValidateEventsSearchTool(options: {
         end,
       });
 
+      // The deployment does not expose the validation endpoint; treat the
+      // candidate as valid so the search can proceed.
+      if (validation === null) {
+        return {
+          valid: true,
+          message:
+            "Events validation is not supported by this Sentry instance; skipped.",
+        };
+      }
+
       recordEventsSearchValidationTelemetry({
         attempt: 0,
         validation,