What Linux kernel version did Android 1.0 use?

Android 1.0 used the Linux 2.6.25 kernel.

Released in September 2008 with the HTC Dream (also sold as the T-Mobile G1), Android 1.0 was built on a Linux-based foundation. The early platform documentation specifically identifies Linux 2.6.25 for ARM as its tested kernel base, matching the ARM processor architecture used by first-generation Android phones.

The kernel is the operating system’s low-level core: it manages memory, processes, hardware drivers, networking, and security boundaries. Android added its own framework, libraries, runtime, and application APIs above that Linux layer, so “Android 1.0” and “Linux 2.6.25” describe different parts of the same software stack.

A common mix-up is Android 1.5, or Cupcake, which moved to Linux 2.6.27. Later Android releases used substantially newer kernels, and manufacturers often customized them for particular chipsets. Thus, the answer refers to the original Android 1.0 platform baseline, not every kernel shipped on every early handset.