What PHP 8.6 changes for WordPress plugins

These are the functions, constants and settings that PHP 8.6 removes, deprecates or no longer ships, with what to use instead. A removed function or constant stops a plugin with a fatal error when that code runs. A deprecated one keeps working and logs a notice.

PHP 8.6 is due on 19 November 2026. This list follows its upgrade notes and can change before the release.

Deprecated

• mb_ereg() and 15 more. Use the preg_ functions with the u modifier.

  mb_ereg(), mb_eregi(), mb_ereg_replace(), mb_eregi_replace(), mb_ereg_replace_callback(), mb_ereg_match(), mb_split(), mb_regex_encoding(), mb_regex_set_options(), mb_ereg_search(), mb_ereg_search_init(), mb_ereg_search_pos(), mb_ereg_search_regs(), mb_ereg_search_getregs(), mb_ereg_search_getpos(), mb_ereg_search_setpos()
• is_long(), is_integer(). Use is_int().
• is_double(). Use is_float().
• doubleval(). Use floatval().
• spl_object_hash(). Use spl_object_id().
• spl_classes(). Use ReflectionExtension::getClassNames().
• strcoll(). Use Collator::compare().
• metaphone(). Use a phonetic matching library.
• mysqli_get_charset(). Use mysqli_character_set_name().
• mysqli_stmt_init(). Use mysqli_prepare().
• SORT_LOCALE_STRING. Use Collator::sort() or Collator::asort().

Bumpcheck also checks syntax changes, such as array offsets with curly braces and constructors named after their class. The full list is on the plugin page.