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PHP Fibers will appear in PHP 8.1 later this year. Fibers are a lightweight flow of execution (also called coroutines) Fibers run in parallel, but they are not sent directly to the CPU. They are similar to threads in a computer program, but are not scheduled by the operating system. PHP core will still be synchronous after Fibers introduced, but that doesn't mean your application can't do two things at the same time. Fibers allow fine control of the main program execution and the Fiber execution.