PHP 8.6, scheduled for release on November 19, 2026, introduces several notable features: partial function application (PFA) for prefilling closure parameters, readonly property defaults (now allowed when implementing interfaces with property hooks), a new low-level Polling API for I/O multiplexing with epoll/WSAPoll backends, a built-in clamp() function, new isReadable/isWriteable reflection methods, function parameter doc comments via ReflectionParameter::getDocComment(), a SortDirection enum, debuggable enums via __debugInfo(), and improved session security defaults (HttpOnly, SameSite=Lax). The release also includes a large set of deprecations covering legacy functions (is_double, is_integer, is_long, doubleval, strcoll, metaphone, spl_classes, spl_object_hash), ArrayIterator methods, SplFileObject CSV methods, returning from finally blocks and constructors/destructors, and reserving keywords like let, is, and namespace for future syntax.