diff --git a/extensions/ql-vscode/CHANGELOG.md b/extensions/ql-vscode/CHANGELOG.md
index d99259b4082..303cb8095fa 100644
--- a/extensions/ql-vscode/CHANGELOG.md
+++ b/extensions/ql-vscode/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## [UNRELEASED]
 
+- Remove support for CodeQL CLI versions older than 2.21.4. [#4285](https://github.com/github/vscode-codeql/pull/4285)
+
 ## 1.17.7 - 5 December 2025
 
 - Rename command "CodeQL: Trim Overlay Base Cache" to "CodeQL: Trim Cache to Overlay-Base" for consistency with "CodeQL: Warm Overlay-Base Cache for [...]" commands. [#4204](https://github.com/github/vscode-codeql/pull/4204)
diff --git a/extensions/ql-vscode/src/codeql-cli/cli.ts b/extensions/ql-vscode/src/codeql-cli/cli.ts
index cf6d5c2e333..a789e499dba 100644
--- a/extensions/ql-vscode/src/codeql-cli/cli.ts
+++ b/extensions/ql-vscode/src/codeql-cli/cli.ts
@@ -45,7 +45,7 @@ import type { LanguageClient } from "vscode-languageclient/node";
  * The oldest version of the CLI that we support. This is used to determine
  * whether to show a warning about the CLI being too old on startup.
  */
-export const OLDEST_SUPPORTED_CLI_VERSION = new SemVer("2.20.7");
+export const OLDEST_SUPPORTED_CLI_VERSION = new SemVer("2.21.4");
 
 /**
  * The version of the SARIF format that we are using.
diff --git a/extensions/ql-vscode/supported_cli_versions.json b/extensions/ql-vscode/supported_cli_versions.json
index c1c48a972bc..2f394bc24b1 100644
--- a/extensions/ql-vscode/supported_cli_versions.json
+++ b/extensions/ql-vscode/supported_cli_versions.json
@@ -3,6 +3,5 @@
   "v2.23.9",
   "v2.22.4",
   "v2.21.4",
-  "v2.20.7",
   "nightly"
 ]