diff --git a/apps/cli/lib/run-wp-cli-command.ts b/apps/cli/lib/run-wp-cli-command.ts
index 92f15a1cfa..897f99a10f 100644
--- a/apps/cli/lib/run-wp-cli-command.ts
+++ b/apps/cli/lib/run-wp-cli-command.ts
@@ -41,6 +41,7 @@ import {
 } from './native-php/php-process';
 import { loadImportedRuntimeStartOptionsNative } from './pull/runtime-start-options';
 import { isServerRunning, sendWpCliCommand } from './wordpress-server-manager';
+import { getWpCliPhpIniArgs, WP_CLI_PHP_INI_ENTRIES } from './wp-cli-php-ini';
 import { stripLeadingShebang } from './wp-cli-shebang';
 import type { SiteData } from 'cli/lib/cli-config/core';
 import type { ReadableStream as WebReadableStream } from 'node:stream/web';
@@ -197,7 +198,13 @@ async function runNativeWpCliCommand(
 	const nativeArgs = applyWpCliCommandOptions( 'native', args, options );
 	const child = spawn(
 		getPhpBinaryPath( phpVersion ),
-		[ ...defaultArgs, getWpCliPharPath(), `--path=${ site.path }`, ...nativeArgs ],
+		[
+			...defaultArgs,
+			...getWpCliPhpIniArgs(),
+			getWpCliPharPath(),
+			`--path=${ site.path }`,
+			...nativeArgs,
+		],
 		{
 			cwd: site.path,
 			stdio: options.stdio === 'inherit' ? 'inherit' : [ 'ignore', 'pipe', 'pipe' ],
@@ -318,6 +325,7 @@ export async function runWpCliCommand(
 			'openssl.cafile': '/tmp/ca-bundle.crt',
 			'curl.cainfo': '/tmp/ca-bundle.crt',
 			allow_url_fopen: 1,
+			...WP_CLI_PHP_INI_ENTRIES,
 		} );
 
 		await php.setSpawnHandler( createNoopSpawnHandler() );
diff --git a/apps/cli/lib/tests/wp-cli-php-ini.test.ts b/apps/cli/lib/tests/wp-cli-php-ini.test.ts
new file mode 100644
index 0000000000..861b476b14
--- /dev/null
+++ b/apps/cli/lib/tests/wp-cli-php-ini.test.ts
@@ -0,0 +1,37 @@
+import { Readable } from 'node:stream';
+import { describe, expect, it } from 'vitest';
+import { WpCliResponse } from 'cli/lib/run-wp-cli-command';
+import { getWpCliPhpIniArgs, WP_CLI_PHP_INI_ENTRIES } from 'cli/lib/wp-cli-php-ini';
+
+const PHP_85_DEPRECATION =
+	'Deprecated: Case statements followed by a semicolon (;) are deprecated, use a colon (:) instead in phar:///wp-cli.phar/vendor/react/promise/src/functions.php on line 369\n';
+const JSON_STDOUT = '[{"name":"akismet","status":"active"}]\n';
+
+describe( 'WP-CLI PHP ini policy', () => {
+	it( 'configures native -d arguments that route diagnostics to stderr', () => {
+		expect( getWpCliPhpIniArgs() ).toEqual( [
+			'-d',
+			`error_reporting=${ WP_CLI_PHP_INI_ENTRIES.error_reporting }`,
+			'-d',
+			'display_errors=stderr',
+			'-d',
+			'log_errors=0',
+		] );
+		expect( Number( WP_CLI_PHP_INI_ENTRIES.error_reporting ) ).toBe( 32767 & ~8192 );
+	} );
+
+	it( 'keeps JSON stdout parseable when PHP diagnostics are on stderr', async () => {
+		expect( () => JSON.parse( `${ PHP_85_DEPRECATION }${ JSON_STDOUT }` ) ).toThrow();
+
+		const response = new WpCliResponse(
+			Readable.from( [ Buffer.from( JSON_STDOUT ) ] ),
+			Readable.from( [ Buffer.from( PHP_85_DEPRECATION ) ] ),
+			Promise.resolve( 0 )
+		);
+
+		expect( JSON.parse( await response.stdoutText ) ).toEqual( [
+			{ name: 'akismet', status: 'active' },
+		] );
+		expect( await response.stderrText ).toBe( PHP_85_DEPRECATION );
+	} );
+} );
diff --git a/apps/cli/lib/wp-cli-php-ini.ts b/apps/cli/lib/wp-cli-php-ini.ts
new file mode 100644
index 0000000000..0f1866ab12
--- /dev/null
+++ b/apps/cli/lib/wp-cli-php-ini.ts
@@ -0,0 +1,15 @@
+const E_ALL = 32767;
+const E_DEPRECATED = 8192;
+
+export const WP_CLI_PHP_INI_ENTRIES = {
+	error_reporting: String( E_ALL & ~E_DEPRECATED ),
+	display_errors: 'stderr',
+	log_errors: 0,
+} as const;
+
+export function getWpCliPhpIniArgs(): string[] {
+	return Object.entries( WP_CLI_PHP_INI_ENTRIES ).flatMap( ( [ key, value ] ) => [
+		'-d',
+		`${ key }=${ value }`,
+	] );
+}