docs: Mention new config system is complete (#17068)

* docs: Mention new config system is complete

* Fix typo

Co-authored-by: Amaresh  S M  <amareshsm13@gmail.com>

---------

Co-authored-by: Milos Djermanovic <milos.djermanovic@gmail.com>
Co-authored-by: Amaresh  S M  <amareshsm13@gmail.com>

Author: 3 people

docs/src/use/configure/configuration-files-new.md

@@ -9,7 +9,7 @@ eleventyNavigation:
 ---
 
 ::: warning
-This is an experimental feature. To opt-in, place an `eslint.config.js` file in the root of your project or set the `ESLINT_USE_FLAT_CONFIG` environment variable to `true`. To opt-out, even in the presence of an `eslint.config.js` file, set the environment variable to `false`. If you are using the API, you can use the configuration system described on this page by using the `FlatESLint` class, the `FlatRuleTester` class, or by setting `configType: "flat"` in the `Linter` class.
+This config system is feature complete but not enabled by default. To opt-in, place an `eslint.config.js` file in the root of your project or set the `ESLINT_USE_FLAT_CONFIG` environment variable to `true`. To opt-out, even in the presence of an `eslint.config.js` file, set the environment variable to `false`. If you are using the API, you can use the configuration system described on this page by using the `FlatESLint` class, the `FlatRuleTester` class, or by setting `configType: "flat"` in the `Linter` class.
 :::
 
 You can put your ESLint project configuration in a configuration file. You can include built-in rules, how you want them enforced, plugins with custom rules, shareable configurations, which files you want rules to apply to, and more.

docs/src/use/configure/configuration-files.md

@@ -8,6 +8,10 @@ eleventyNavigation:
 
 ---
 
+::: warning
+We are transitioning to a new config system in ESLint v9.0.0. The config system shared on this page is currently the default but will be deprecated in v9.0.0. You can opt-in to the new config system by following the instructions in the [documentation](configuration-files-new).
+:::
+
 You can put your ESLint project configuration in a configuration file. You can include built-in rules, how you want them enforced, plugins with custom rules, shareable configurations, which files you want rules to apply to, and more.
 
 ## Configuration File Formats