diff --git a/CHANGELOG.md b/CHANGELOG.md
index bb4d0129e5..b023f376bc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,7 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 
 ## [UNRELEASED]
 
-No user facing changes.
+- CodeQL Action v3 will be deprecated in December 2026.  The Action now logs a warning for customers who are running v3 but could be running v4. For more information, see [Upcoming deprecation of CodeQL Action v3](https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/).
 
 ## 4.31.2 - 30 Oct 2025
 
diff --git a/lib/analyze-action.js b/lib/analyze-action.js
index 04fac76278..07eeb5eb3b 100644
--- a/lib/analyze-action.js
+++ b/lib/analyze-action.js
@@ -87413,14 +87413,14 @@ async function checkDiskUsage(logger) {
   }
 }
 function checkActionVersion(version, githubVersion) {
-  if (!semver.satisfies(version, ">=3") && // do not log error if the customer is already running v3
+  if (!semver.satisfies(version, ">=4") && // do not log error if the customer is already running v4
   !process.env["CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */]) {
     if (githubVersion.type === 0 /* DOTCOM */ || githubVersion.type === 2 /* GHE_DOTCOM */ || githubVersion.type === 1 /* GHES */ && semver.satisfies(
       semver.coerce(githubVersion.version) ?? "0.0.0",
-      ">=3.11"
+      ">=3.20"
     )) {
       core3.error(
-        "CodeQL Action major versions v1 and v2 have been deprecated. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/"
+        "CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/"
       );
       core3.exportVariable("CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */, "true");
     }
diff --git a/lib/autobuild-action.js b/lib/autobuild-action.js
index 94f3208a99..298f50dbcd 100644
--- a/lib/autobuild-action.js
+++ b/lib/autobuild-action.js
@@ -83157,14 +83157,14 @@ async function checkDiskUsage(logger) {
   }
 }
 function checkActionVersion(version, githubVersion) {
-  if (!semver.satisfies(version, ">=3") && // do not log error if the customer is already running v3
+  if (!semver.satisfies(version, ">=4") && // do not log error if the customer is already running v4
   !process.env["CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */]) {
     if (githubVersion.type === 0 /* DOTCOM */ || githubVersion.type === 2 /* GHE_DOTCOM */ || githubVersion.type === 1 /* GHES */ && semver.satisfies(
       semver.coerce(githubVersion.version) ?? "0.0.0",
-      ">=3.11"
+      ">=3.20"
     )) {
       core3.error(
-        "CodeQL Action major versions v1 and v2 have been deprecated. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/"
+        "CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/"
       );
       core3.exportVariable("CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */, "true");
     }
diff --git a/lib/init-action.js b/lib/init-action.js
index 9cd3723250..456989a4ab 100644
--- a/lib/init-action.js
+++ b/lib/init-action.js
@@ -84734,14 +84734,14 @@ async function checkDiskUsage(logger) {
   }
 }
 function checkActionVersion(version, githubVersion) {
-  if (!semver.satisfies(version, ">=3") && // do not log error if the customer is already running v3
+  if (!semver.satisfies(version, ">=4") && // do not log error if the customer is already running v4
   !process.env["CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */]) {
     if (githubVersion.type === 0 /* DOTCOM */ || githubVersion.type === 2 /* GHE_DOTCOM */ || githubVersion.type === 1 /* GHES */ && semver.satisfies(
       semver.coerce(githubVersion.version) ?? "0.0.0",
-      ">=3.11"
+      ">=3.20"
     )) {
       core3.error(
-        "CodeQL Action major versions v1 and v2 have been deprecated. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/"
+        "CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/"
       );
       core3.exportVariable("CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */, "true");
     }
diff --git a/lib/resolve-environment-action.js b/lib/resolve-environment-action.js
index 4f6d48f3f9..03a9bf9e29 100644
--- a/lib/resolve-environment-action.js
+++ b/lib/resolve-environment-action.js
@@ -83169,14 +83169,14 @@ async function checkDiskUsage(logger) {
   }
 }
 function checkActionVersion(version, githubVersion) {
-  if (!semver.satisfies(version, ">=3") && // do not log error if the customer is already running v3
+  if (!semver.satisfies(version, ">=4") && // do not log error if the customer is already running v4
   !process.env["CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */]) {
     if (githubVersion.type === 0 /* DOTCOM */ || githubVersion.type === 2 /* GHE_DOTCOM */ || githubVersion.type === 1 /* GHES */ && semver.satisfies(
       semver.coerce(githubVersion.version) ?? "0.0.0",
-      ">=3.11"
+      ">=3.20"
     )) {
       core3.error(
-        "CodeQL Action major versions v1 and v2 have been deprecated. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/"
+        "CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/"
       );
       core3.exportVariable("CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */, "true");
     }
diff --git a/lib/setup-codeql-action.js b/lib/setup-codeql-action.js
index 18b293b2a8..b7e7ec6ca3 100644
--- a/lib/setup-codeql-action.js
+++ b/lib/setup-codeql-action.js
@@ -83245,14 +83245,14 @@ async function checkDiskUsage(logger) {
   }
 }
 function checkActionVersion(version, githubVersion) {
-  if (!semver.satisfies(version, ">=3") && // do not log error if the customer is already running v3
+  if (!semver.satisfies(version, ">=4") && // do not log error if the customer is already running v4
   !process.env["CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */]) {
     if (githubVersion.type === 0 /* DOTCOM */ || githubVersion.type === 2 /* GHE_DOTCOM */ || githubVersion.type === 1 /* GHES */ && semver.satisfies(
       semver.coerce(githubVersion.version) ?? "0.0.0",
-      ">=3.11"
+      ">=3.20"
     )) {
       core3.error(
-        "CodeQL Action major versions v1 and v2 have been deprecated. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/"
+        "CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/"
       );
       core3.exportVariable("CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */, "true");
     }
diff --git a/lib/upload-sarif-action.js b/lib/upload-sarif-action.js
index f927d490f9..65e75b23f7 100644
--- a/lib/upload-sarif-action.js
+++ b/lib/upload-sarif-action.js
@@ -86065,14 +86065,14 @@ async function checkDiskUsage(logger) {
   }
 }
 function checkActionVersion(version, githubVersion) {
-  if (!semver.satisfies(version, ">=3") && // do not log error if the customer is already running v3
+  if (!semver.satisfies(version, ">=4") && // do not log error if the customer is already running v4
   !process.env["CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */]) {
     if (githubVersion.type === 0 /* DOTCOM */ || githubVersion.type === 2 /* GHE_DOTCOM */ || githubVersion.type === 1 /* GHES */ && semver.satisfies(
       semver.coerce(githubVersion.version) ?? "0.0.0",
-      ">=3.11"
+      ">=3.20"
     )) {
       core3.error(
-        "CodeQL Action major versions v1 and v2 have been deprecated. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/"
+        "CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/"
       );
       core3.exportVariable("CODEQL_ACTION_DID_LOG_VERSION_DEPRECATION" /* LOG_VERSION_DEPRECATION */, "true");
     }
diff --git a/src/util.test.ts b/src/util.test.ts
index 0e3adc8f7e..03d7d89ec2 100644
--- a/src/util.test.ts
+++ b/src/util.test.ts
@@ -447,13 +447,21 @@ const CHECK_ACTION_VERSION_TESTS: Array<[string, util.GitHubVersion, boolean]> =
     ["2.2.1", { type: util.GitHubVariant.DOTCOM }, true],
     ["2.2.1", { type: util.GitHubVariant.GHE_DOTCOM }, true],
     ["2.2.1", { type: util.GitHubVariant.GHES, version: "3.10" }, false],
-    ["2.2.1", { type: util.GitHubVariant.GHES, version: "3.11" }, true],
-    ["2.2.1", { type: util.GitHubVariant.GHES, version: "3.12" }, true],
-    ["3.2.1", { type: util.GitHubVariant.DOTCOM }, false],
-    ["3.2.1", { type: util.GitHubVariant.GHE_DOTCOM }, false],
+    ["2.2.1", { type: util.GitHubVariant.GHES, version: "3.11" }, false],
+    ["2.2.1", { type: util.GitHubVariant.GHES, version: "3.12" }, false],
+    ["3.2.1", { type: util.GitHubVariant.DOTCOM }, true],
+    ["3.2.1", { type: util.GitHubVariant.GHE_DOTCOM }, true],
     ["3.2.1", { type: util.GitHubVariant.GHES, version: "3.10" }, false],
     ["3.2.1", { type: util.GitHubVariant.GHES, version: "3.11" }, false],
     ["3.2.1", { type: util.GitHubVariant.GHES, version: "3.12" }, false],
+    ["3.2.1", { type: util.GitHubVariant.GHES, version: "3.19" }, false],
+    ["3.2.1", { type: util.GitHubVariant.GHES, version: "3.20" }, true],
+    ["3.2.1", { type: util.GitHubVariant.GHES, version: "3.21" }, true],
+    ["4.2.1", { type: util.GitHubVariant.DOTCOM }, false],
+    ["4.2.1", { type: util.GitHubVariant.GHE_DOTCOM }, false],
+    ["4.2.1", { type: util.GitHubVariant.GHES, version: "3.19" }, false],
+    ["4.2.1", { type: util.GitHubVariant.GHES, version: "3.20" }, false],
+    ["4.2.1", { type: util.GitHubVariant.GHES, version: "3.21" }, false],
   ];
 
 for (const [
@@ -480,9 +488,7 @@ for (const [
     if (shouldReportError) {
       t.true(
         warningSpy.calledOnceWithExactly(
-          sinon.match(
-            "CodeQL Action major versions v1 and v2 have been deprecated.",
-          ),
+          sinon.match("CodeQL Action v3 will be deprecated in December 2026."),
         ),
       );
     } else {
diff --git a/src/util.ts b/src/util.ts
index 96ea0f9da2..7136119c5a 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -1114,38 +1114,38 @@ export async function checkDiskUsage(
 }
 
 /**
- * Prompt the customer to upgrade to CodeQL Action v3, if appropriate.
+ * Prompt the customer to upgrade to CodeQL Action v4, if appropriate.
  *
- * Check whether a customer is running v1 or v2. If they are, and we can determine that the GitHub
- * instance supports v3, then log an error prompting the customer to upgrade to v3.
+ * Check whether a customer is running v3. If they are, and we can determine that the GitHub
+ * instance supports v4, then log an error prompting the customer to upgrade to v4.
  */
 export function checkActionVersion(
   version: string,
   githubVersion: GitHubVersion,
 ) {
   if (
-    !semver.satisfies(version, ">=3") && // do not log error if the customer is already running v3
+    !semver.satisfies(version, ">=4") && // do not log error if the customer is already running v4
     !process.env[EnvVar.LOG_VERSION_DEPRECATION] // do not log error if we have already
   ) {
-    // Only error for versions of GHES that are compatible with CodeQL Action version 3.
+    // Only error for versions of GHES that are compatible with CodeQL Action version 4.
     //
-    // GHES 3.11 shipped without the v3 tag, but it also shipped without this warning message code.
-    // Therefore users who are seeing this warning message code have pulled in a new version of the
-    // Action, and with it the v3 tag.
+    // GHES 3.20 is the first version to ship with the v4 tag and this warning message code.
+    // Therefore, users who are seeing this warning message code are running on GHES 3.20 or newer,
+    // and should update to CodeQL Action v4.
     if (
       githubVersion.type === GitHubVariant.DOTCOM ||
       githubVersion.type === GitHubVariant.GHE_DOTCOM ||
       (githubVersion.type === GitHubVariant.GHES &&
         semver.satisfies(
           semver.coerce(githubVersion.version) ?? "0.0.0",
-          ">=3.11",
+          ">=3.20",
         ))
     ) {
       core.error(
-        "CodeQL Action major versions v1 and v2 have been deprecated. " +
-          "Please update all occurrences of the CodeQL Action in your workflow files to v3. " +
+        "CodeQL Action v3 will be deprecated in December 2026. " +
+          "Please update all occurrences of the CodeQL Action in your workflow files to v4. " +
           "For more information, see " +
-          "https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/",
+          "https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/",
       );
       // set LOG_VERSION_DEPRECATION env var to prevent the warning from being logged multiple times
       core.exportVariable(EnvVar.LOG_VERSION_DEPRECATION, "true");