People familiar with the first OS X 10.9.1 beta said it is identified as "build 13B27." The pre-release software is intended for testing purposes, and is not yet finalized for public release.
OS X 10.9.1 will presumably mark the first update for Mavericks since it debuted on the Mac App Store for free in late October. All Mac users with compatible systems running Snow Leopard or above can upgrade to Mavericks at no cost.
A minor update for Mavericks was issued last week to patch an issue with the native Mail app for Gmail users. It was issued via the Mac App Store.
Mavericks, named after a Northern California surf spot, brings several new features to the OS X operating system, though Apple also paid considerable attention to enhancing performance and battery life with its latest major release. Stats published soon after the release of Mavericks found that public adoption was three times faster than that of Apple's $20 Mountain Lion upgrade from 2012.
As Apple prepares its first maintenance update for Mavericks, the company is also working on its next major OS X release, version 10.10. Traffic data to AppleInsider published earlier this month revealed that testing of the unnamed future operating system has been growing steadily.