Pre-Whistler

Odyssey - Not much is known about this build, as it was never leaked. It is only known that it was merged with Neptune to become Whistler.

Neptune 5111 - Almost identical to Windows 2000. The only changes were basically speed and a new HTML Help. This is pre-Whistler. It was combined with Odyssey to form Whistler.  -December 27, 1999

Whistler

Whistler 2211 - The first leaked Whistler build. Basically Neptune, with some minor bug fixes. -March 20, 2000

Whistler 2223.1 - Still no major changes from Windows 2000. There were some minor GUI updates in this build. April 17, 2000

Whistler 2239 - The first Whistler Advanced Server build. It had an updated Configure your Server wizard, as well as some GUI changes.

Whistler 2250 - The first major change from Windows 2000. This was the first build that included support for Visual Styles. It shipped with an obviously unfinished and buggy one, but it worked. Any build before this was an internal leak. -July 13, 2000

Whistler 2257 - This build improved upon the theme in 2250 with the beginnings of the well-known Watercolor theme. It had the first new-style start menu (2250 had it, but it was hidden). -Internal leak -August 24, 2000

Whistler 2267 - Another Advanced Server build. This included the Watercolor theme, as well as more enhancements to the Configure your Server wizard, among others. -October 3, 2000

Whistler 2276 - This build contained a new background wallpaper, and more enhancements to the Watercolor theme, but it was much buggier than previous builds. This was another official build.

Whistler 2287 - This was basically a massive bug fix for 2276. It was much more stable than 2276, and contained slight changes to the UI as well. Another official build.

Whistler 2296 (Beta 1) - This was the first major milestone build for Whistler. It provided many UI enhancements, especially in the Explorer folder views. -October 31, 2000

Whistler 2410 - This build saw a massive update to the Watercolor theme. Being over 100 builds from Beta 1, it contained many changes. The icons were completely different, the start menu was enhanced, the Explorer folder view was further changed, and there were many, many bug fixes. -January 4, 2001

Whistler 2416 - This build featured another new icon set, as well as a larger start menu than 2410. -January 16, 2001

Whistler 2419 - This was not that much of a change from 2416, except for 2 things: 1, the start menu was bloated even further than it already was, and 2, this was the first build containing Windows Product Activation. This was the last build to contain the Watercolor theme. -January 23, 2001

Whistler 2428 - Luna. Need I say more? I hope not, because that's about it; Luna replaced Watercolor as the theme, and the logon screen was changed. -February 13, 2001

Whistler 2439 - Speed enhancements, slight UI improvements. -Internal leak

Whistler 2446 - This build featured many enhancements to the Luna UI, including a divider arrow between the taskbar and systray and some new wallpapers. -March 5, 2001

Whistler 2454 - Not much different from 2446; a couple bug fixes, driver updates, etc. -Internal leak

Whistler 2458 - Noticeably faster than 2454, and not as buggy.

Whistler 2462 (Beta 2) - This had to be the biggest release of Whistler. Not that much was changed from 245x, except for speed improvements and logon screen enhancements, but over 400 people hit #windowsxp for about a week straight, and it was probably similar other places too. -March 23, 2001

Whistler 2463 - One bug with remote desktop corrected. -Internal leak
 

Windows XP

Windows XP 2465 - The first interim after Beta 2, and probably the buggiest as well. This contained a new background wallpaper set, and the UI said Windows XP in many places instead of Whistler for the first time. However, it caused problems with certain programs, including Office XP, and was generally unstable. -April 26, 2001

Windows XP 2469 - This was the first build that was very hard to crack. Well, no, not hard: impossible. There was never a true crack for this build. The Reset workaround was developed for this build. Direct3D didn't work in 2469 either, so this was a very unpopular build. -May 12, 2001

Windows XP 2474 - The first build which contained Windows Messenger, which is basically MSN Messenger combined with NetMeeting. The build was buggy and somewhat slow, but that's to be expected of internal leaks, which this was.

Windows XP 2475 - This build was almost identical to 2474, but less buggy, and it did not have Windows Messenger in it. -May 24, 2001

Windows XP 2481 - Finally, a major update to the UI. This build had 2 new themes, Metallic and Homestead. It also boasted a major improvement in speed and stability over 2475. This build was leaked to IRC before MS released it to technical beta testers. -June 6, 2001

Windows XP 2485 - This build was faster than 2481, but not quite as stable. -Internal leak

Windows XP 2486 - Speed of 2485, stability of 2481, and renamed themes to Silver and Olive. -June 15, 2001

Windows XP 2494 - Not much different from 2486. Microsoft was just polishing up for RC1 in this build. -June 21, 2001

Windows XP 2495 - This build actually leaked before 2494 was released, so there must have been something wrong with it, but nobody really found out what. If you know, let us know :) -Internal leak

Windows XP 2498 - Nobody really cared about this build, because it leaked at the same time as 2499, so I don't have any info on it. If you do, let me know. -Internal leak

Windows XP 2499 - Nobody really cared about this build either, to tell the truth. It had some improvements over 94/95 in speed, and some bug fixes, but that's really about it. -Internal leak

Windows XP 2502 - Speed, bug fixes, blah blah; you wont hear that much after this, really :)

Windows XP 2504 - Once again, speed improvements, bug fixes -Internal leak

Windows XP 2505 (Release Candidate 1) - The first feature-complete version of XP. This was the first build available to the public, except for beta 2 if you were one of the first 20,000 people to sign up for the Windows Preview Program. -June 29, 2001

Windows XP 2509 - Very buggy build. Some DirectX things didn't work properly or at all. IE version contained commas instead of periods, which isn't that big of a deal, but it's still kind of funny :) -Internal leak

Windows XP 2517 - Fixed many of the bugs in 2509, and was faster, too. -Internal leak

Windows XP 2520 - The only interim between RC1 and RC2. Stable and fast. -July 24, 2001

Windows XP 2525 - Bug fixes from 2520. -Internal leak

Windows XP 2526 (Release Candidate 2) - Faster than 2520 and less buggy, and performs better in Quake 3 than any other build according to A-KO^. -July 28, 2001

Windows XP 2531 - Not too different from RC2. Slightly faster. -Internal leak

Windows XP 2532 - Almost identical to 2531. Only a couple bug fixes, most likely. -Internal leak

Windows XP 2535 - Bug fixes, and the wallpaper reverted to the old grassy one as opposed to the newer Windows logo backgrounds. -August 7th

Windows XP 2542 - Bug fixes, and finalized WPA. Previous keys do not work on this build. Beta tester keys work for 30 days instead of 14 with no activation. Pro and home have separate keys now.

Windows XP 2600 - Not much changed except for the jump in builds. -Internal leak

Windows XP 2600 (RTM) - The same as build 2600 that was leaked, but no 180 day time bomb. -August 24, 2001