Pre-release Update 1 was released on October 10, 2004. Version numbers are:

Kickstart 51.15
Workbench 51.1
U-Boot 1.1.1 (04-Oct-2004)

This release is available as a free update and bundled with new AmigaOnes. It adds support for the MicroA1 (ľA1). The official list of things included in the update is:

• Kernel-Level Altivec support.
• Much improved compatibility/speed of 68k emulation (JIT not included yet).
• Improved 68k FPU emulation.
• Fully PowerPC-native Picasso96/graphics system.
• Fully PowerPC-native MUI.
• USB support for input devices.
• Support for onboard serial and parallel hardware.
• Driver support for the SiI0680 IDE adaptor (including UDMA support).
• Improved PIO mode VIA driver.
• Improved Internet capabilities and better Ethernet support.
• Printing support.
• Improved audio hardware support, including new drivers.
• Comprehensive bug fixes, speed improvements, added features and functionality across all system components.
• and much more...

Shown in the Workbench 1 screenshot are some of the following features:

• Underlined icon is a filesystem link (in this case a soft-link to a disk, the information window below shows where it links to) (v50).
• Default icons can now be made transparent (such as the Projects icon, the underlined Music one is a real icon) (v51).
• "Assign" and "Mount" options on the "insert disk" requester. (new for v51).
• The little boxes on the Shell and USBInspector icons signify that they are "left out" (new for v51).
• Screen titlebar is configurable (v50, updated in v51).
• DOS Preferences (new for v51).
• Workbench Preferences (updated for v51).
• USB Preferences (new for v51).
• USB Inspector (new for v51).
• KeyShow now correctly shows the layout of a PC keyboard (v50 showed an Amiga keyboard—I assume it now looks at the keymap setting in Input prefs).
• The Grim Reaper (updated for v51).
• Ram Disk is now RAM Disk (v51).