diff --git a/lib/entry-points.js b/lib/entry-points.js
index f46c91b54..93c634319 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -186044,6 +186044,8 @@ async function getToolsInput(action, repositoryProperties) {
 }
 
 // src/languages/swift.ts
+var SWIFT_TRACED_UNSUPPORTED_MACOS = 27;
+var SWIFT_TRACED_UNSUPPORTED_XCODE = 27;
 async function isSwiftCompatible(action, config, codeql) {
   if (!config.languages.includes("swift" /* swift */)) {
     return;
@@ -186063,6 +186065,35 @@ async function isSwiftCompatible(action, config, codeql) {
     );
     return;
   }
+  if (version.major >= SWIFT_TRACED_UNSUPPORTED_MACOS) {
+    const baseMessage = [
+      `Traced Swift analysis is not supported on macOS ${SWIFT_TRACED_UNSUPPORTED_MACOS} or above.`,
+      `Configure your analysis to run on macOS ${SWIFT_TRACED_UNSUPPORTED_MACOS - 1} or below`,
+      `and XCode ${SWIFT_TRACED_UNSUPPORTED_XCODE - 1} or below.`
+    ].join(" ");
+    action.logger.warning(baseMessage);
+    addDiagnostic(
+      config,
+      "swift" /* swift */,
+      makeDiagnostic(
+        "codeql-action/unsupported-traced-swift-analysis-macos",
+        "Traced Swift analysis is not supported on this version of macOS",
+        {
+          attributes: {
+            languages: config.languages,
+            macOSVersion: version.toString()
+          },
+          markdownMessage: baseMessage,
+          severity: "warning",
+          visibility: {
+            cliSummaryTable: true,
+            statusPage: true,
+            telemetry: true
+          }
+        }
+      )
+    );
+  }
 }
 
 // src/status-report/tools-download.ts
diff --git a/src/languages/swift.test.ts b/src/languages/swift.test.ts
index 745f631b5..152775682 100644
--- a/src/languages/swift.test.ts
+++ b/src/languages/swift.test.ts
@@ -2,6 +2,7 @@ import test from "ava";
 import * as sinon from "sinon";
 
 import { getCodeQLForTesting } from "../codeql";
+import * as diagnostics from "../diagnostics";
 import { ActionsEnvVars } from "../environment";
 import {
   checkExpectedLogMessages,
@@ -10,6 +11,7 @@ import {
   initAllState,
   makeVersionInfo,
   RecordingLogger,
+  setupTests,
 } from "../testing-utils";
 import { ToolsFeature } from "../tools-features";
 import { withTmpDir } from "../util";
@@ -18,6 +20,8 @@ import { isSwiftCompatible } from "./swift";
 
 import { BuiltInLanguage } from ".";
 
+setupTests(test);
+
 test("isSwiftCompatible doesn't throw for non-Swift languages", async (t) => {
   for (const language of Object.values(BuiltInLanguage)) {
     if (language === BuiltInLanguage.swift) {
@@ -128,3 +132,60 @@ test("isSwiftCompatible warns if version string is not a semver", async (t) =>
       "Unable to determine version of macOS, got: unexpected",
     ]);
   }));
+
+// `addDiagnostic` changes global state and we must stub it, so this test must be serial.
+test.serial(
+  "isSwiftCompatible logs and adds diagnostic if macOS version is unsupported",
+  async (t) =>
+    withTmpDir(async (tmpDir) => {
+      const logger = new RecordingLogger();
+      const env = getTestEnv();
+      env.set(ActionsEnvVars.RUNNER_TEMP, tmpDir);
+
+      const codeql = await getCodeQLForTesting(
+        "codeql-for-testing",
+        logger,
+        env,
+      );
+      sinon.stub(codeql, "getVersion").resolves(makeVersionInfo("2.27.0"));
+
+      const addDiagnostic = sinon.stub(diagnostics, "addDiagnostic");
+
+      const config = createTestConfig({ languages: [BuiltInLanguage.swift] });
+      await isSwiftCompatible(
+        initAllState({
+          logger,
+          platform: "darwin",
+          osRelease: "27.0.0",
+          env,
+        }),
+        config,
+        codeql,
+      );
+
+      checkExpectedLogMessages(t, logger.messages, [
+        "Traced Swift analysis is not supported on macOS 27",
+      ]);
+
+      t.is(addDiagnostic.callCount, 1);
+      t.like(addDiagnostic.args[0], [
+        config,
+        BuiltInLanguage.swift,
+        {
+          attributes: {
+            languages: [BuiltInLanguage.swift],
+            macOSVersion: "27.0.0",
+          },
+          source: {
+            id: "codeql-action/unsupported-traced-swift-analysis-macos",
+            name: "Traced Swift analysis is not supported on this version of macOS",
+          },
+          visibility: {
+            cliSummaryTable: true,
+            statusPage: true,
+            telemetry: true,
+          },
+        } satisfies Partial<diagnostics.DiagnosticMessage>,
+      ]);
+    }),
+);
diff --git a/src/languages/swift.ts b/src/languages/swift.ts
index 3b6d70959..21172951b 100644
--- a/src/languages/swift.ts
+++ b/src/languages/swift.ts
@@ -1,12 +1,19 @@
 import { ActionState } from "../action-common";
 import { CodeQL } from "../codeql";
 import { Config } from "../config-utils";
+import { addDiagnostic, makeDiagnostic } from "../diagnostics";
 import { macOSVersion } from "../platform";
 import { ToolsFeature } from "../tools-features";
 import { ConfigurationError } from "../util";
 
 import { BuiltInLanguage } from ".";
 
+/** macOS 27 and above do not support traced extraction for Swift. */
+export const SWIFT_TRACED_UNSUPPORTED_MACOS = 27;
+
+/** Xcode 27 and above do not support traced extraction for Swift. */
+export const SWIFT_TRACED_UNSUPPORTED_XCODE = 27;
+
 /**
  * Determines whether we can run a Swift analysis on the current runner.
  *
@@ -49,4 +56,38 @@ export async function isSwiftCompatible(
     );
     return;
   }
+
+  if (version.major >= SWIFT_TRACED_UNSUPPORTED_MACOS) {
+    const baseMessage = [
+      `Traced Swift analysis is not supported on macOS ${SWIFT_TRACED_UNSUPPORTED_MACOS} or above.`,
+      `Configure your analysis to run on macOS ${SWIFT_TRACED_UNSUPPORTED_MACOS - 1} or below`,
+      `and XCode ${SWIFT_TRACED_UNSUPPORTED_XCODE - 1} or below.`,
+    ].join(" ");
+
+    // Log the message. This will also show up as a workflow annotation.
+    action.logger.warning(baseMessage);
+
+    // Create a diagnostic that will show up on the TSP.
+    addDiagnostic(
+      config,
+      BuiltInLanguage.swift,
+      makeDiagnostic(
+        "codeql-action/unsupported-traced-swift-analysis-macos",
+        "Traced Swift analysis is not supported on this version of macOS",
+        {
+          attributes: {
+            languages: config.languages,
+            macOSVersion: version.toString(),
+          },
+          markdownMessage: baseMessage,
+          severity: "warning",
+          visibility: {
+            cliSummaryTable: true,
+            statusPage: true,
+            telemetry: true,
+          },
+        },
+      ),
+    );
+  }
 }