Site Kit by Google on PHP 8.6: deprecation notices and the fix

On PHP 8.6 (due 19 November 2026), Site Kit by Google 1.190.0 logs deprecation notices when the affected code runs. We found 4 places in its code that PHP 8.6 flags. Nothing stops working; the notices go to your PHP error log and show on pages where errors are displayed.

Tested on 28 October 2026 with the official PHP 8.6.0RC4 build and WordPress 7.1.1, plugin version 1.190.0 (5,000,000+ active installs) from WordPress.org, activated alone with default settings.

The messages you will see

Deprecated: Function is_integer() is deprecated since 8.6, use is_int() instead

Deprecated: Function spl_object_hash() is deprecated since 8.6, consider using spl_object_id() instead

Deprecated: Using "is" as a class name is deprecated since 8.6

Where they come from

File:line	What	When PHP 8.6 complains	In our WordPress test
`includes/Core/Expirables/Expirable_Items.php:125`	calls `is_integer()` / `is_long()` `if ( is_integer( $ttl ) ) {`	When this code runs	not on the pages we opened
`third-party/guzzlehttp/guzzle/src/HandlerStack.php:244` (bundled library)	calls `spl_object_hash()` `return 'callable(' . \spl_object_hash($fn) . ')';`	When this code runs	not on the pages we opened
`third-party/guzzlehttp/promises/src/Is.php:6` (bundled library)	bundled Guzzle Promises `Is` class	Compile time: logged when PHP loads the file	not on the pages we opened
`third-party/phpseclib/phpseclib/phpseclib/Net/SSH2.php:4746` (bundled library)	calls `spl_object_hash()` `return '{' . spl_object_hash($this) . '}';`	When this code runs	not on the pages we opened

The fix

Site owners: you don't need to change anything to keep the site working. Keep display_errors off on the live site, and update Site Kit by Google when a release mentions PHP 8.6. If a notice shows on your pages, set define( 'WP_DEBUG_DISPLAY', false ); in wp-config.php.

Plugin developers, line by line:

calls is_integer() / is_long(): Use is_int().
calls spl_object_hash(): Use spl_object_id(), or update the bundled library that calls it.
bundled Guzzle Promises Is class: This is the bundled Guzzle Promises library's Is class. Update the bundled guzzlehttp/promises to 2.6.0 or 3.1.0 (released 18 October 2026), which use the new State class internally.

What a PHP 8.6 deprecation notice does, and what it doesn't

Nothing stops working on PHP 8.6. A deprecation is a warning that the code will break in a future major version (PHP 9, no date yet). The plugin keeps working.
It lands in your logs. With log_errors on (the usual hosting default) every notice goes to the PHP error log, and with WP_DEBUG_LOG to wp-content/debug.log.
It can show on the page. If display_errors is on, or WP_DEBUG is on without WP_DEBUG_DISPLAY set to false, the notice is printed into the page. That breaks AJAX/JSON responses and can cause "headers already sent" warnings. Keep display off on live sites.
Compile-time notices are logged when PHP compiles the file. With OPcache that happens once after a restart or cache reset, so you see a few lines, not one per visit. Function notices (spl_object_hash(), is_integer()…) are logged every time that code runs.

All 39 affected plugins out of the 100 most popular, and the 61 with no findings: PHP 8.6 and WordPress plugins.

Sources

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