Downloading and installing Flex SDK builds from

The Flex SDK is constantly changing and improving. Every day bugs are getting fixed, features are being added or improved. If you want to use the latest code, you’ll need to know where to download the Flex SDK from and how to add the new SDK to Flex Builder.

New builds of the Flex SDK can be downloaded from the Flex SDK Downloads page on the site. Currently, this page gives you links to download the latest Gumbo nightly build, the latest Flex 3 nightly build, or the various Flex 3 Compiler Modules. There are three main SDK build types:

  • Latest Milestone Release Builds — Releases are builds that have been declared major releases by the development team – Releases are the right builds for people who want to be on a stable, tested release, and don’t need the latest greatest features and improvements. There are generally a few milestone releases on a given branch and will be signified by incrementing the first minor number (e.g., 3.1).

    The Flex team creates signed versions of the major RSLs for every milestone release.

  • Stable Builds — Stable builds have been found to be stable enough for most people to use. They are promoted from nightly build by the architecture team after they have been used for a few days and deemed reasonable. The latest stable build is the right build for people who want to stay up to date with what is going on in the latest development stream, and don’t mind putting up with a few problems in order to get the latest and greatest features and bug fixes. The latest stable build is the one the development team likes people to be using because of the valuable and timely feedback; however it should be understood that the only fully supported versions are milestones (e.g., Adobe technical support supports milestones, though may point to fixes in stable builds) . The development team attempts to put out a stable build on active branches within 60 days of each other. Stable builds are signified by incrementing the second minor number (e.g., 3.0.1).

    The Flex team dos not currently create signed versions of the major RSLs for stable builds as it would begin negating the value of the framework cache (that said, we’ll be keeping an eye on things and re-evaluating as necessary).

  • Nightly Builds — Nightly builds are produced every night from whatever has been released into the HEAD of the SVN repository. They are untested and may have problems. Some possibly will not work at all. These drops are normally only useful to developers actually working on the Flex Project, but may be used to monitor how a given feature is progressing. Nightly builds follow the numbering of the last stable build, with only the third minor number incrementing (and matching the last revision number from Subversion).

[source SDK Build Types]

The next important thing to understand is the different types of Flex SDKs available:

  • Free Adobe Flex SDK — An official Adobe product, with released versions found at The Adobe Flex SDK contains everything you will need to build and deploy Flex RIAs. It is licensed under the Adobe Flex SDK license because it contains a mixture of open and closed source components (see license info above). The Flex framework source code included in this package is called out explicitly as licensed under the MPL. However, if you want just the open source stuff, you should look at the Open Source Flex SDK.
  • Open Source Flex SDK — For users who want a package that contains only open source code, we offer the Open Source Flex SDK, which is available from this site. This package is entirely under the MPL, including its binaries. It contains the majority of the Flex SDK (compilers, framework, debugger) but does not include anything that is not open source like the Adobe Flash Player, Adobe AIR, or the advanced font encoding libraries. This SDK is capable of creating Flex applications and can be used in whatever fashion the MPL allows. If you have questions regarding the use of code licensed under the MPL, you should consult with an attorney.
  • Adobe Add-ons for Open Source Flex SDK — This package contains all of the items that are in the Adobe Flex SDK and not in the Open Source Flex SDK. Downloading this file will allow you to bring the Open Source Flex SDK to parity with the Adobe Flex SDK. This package includes the Adobe Flash Player, Adobe AIR, the advanced font encoding libraries, and the code that allows licensing of things like the Data Visualization components. All of these elements are licensed under the Adobe Flex SDK license.

[source Flex SDK Downloads]

Downloading and installing Flex SDK builds into Flex Builder 3

  1. To download the Flex 3 SDK, navigate to the following URL:
  2. Download the latest nightly build. You can download either of the available SDK types (Adobe Flex SDK, Open Source Flex SDK, or Adobe Add-ons — see the previous list for explanations between the differnt types). For this example I am downloading the latest nightly build of the Adobe Flex SDK.
  3. Save the nightly build to your hard drive and extract the files from the .ZIP file
  4. In Flex Builder 3, select Window > Preferences from the main menu to open the Flex Builder Preferences dialog box. To add, edit, or remove a Flex SDK, select Flex > Installed Flex SDKs.
  5. Click the Add button to launch the Add Flex SDK dialog box and click the Browse button to navigate to the directory where you extracted the nightly SDK build in a previous step.
  6. Click OK to apply your changes and add the new Flex SDK. If you want to set the newly downloaded SDK as your default SDK, click the check box to the left of the SDK name. Click OK to dismiss this dialog.

That’s it! You’ve successfully downloaded and installed the latest and greatest version of the Flex SDK into Flex Builder.

If you want to compile your code against this new SDK you can select Project > Properties from the main menu, select Flex Compiler from the menu on the left, and select your new SDK from the dropdown menu in the Flex SDK version section.

Also worth mentioning is that you can manage your installed SDKs via the Project Properties dialog menu by clicking the Configure Flex SDKs link, which takes you to the Installed Flex SDKs preferences.

Happy Flexing!

24 thoughts on “Downloading and installing Flex SDK builds from

  1. Thks Peter,

    I’ll try to upgrade it now ;), because I’ve tried an SDK and it show me “This component is based on ?????, which is not a visuel component. Switch to source mode to edit it.”

    When I be back to SDK 3.0, It doesn’t show that msg…

    thks Peter,

  2. Still having the same msg, I’ve tested todays version of SDK “Thu Aug 21, 2008”

    I think I miss something like copy some files from 3.0 SDK, any Idea?

    Thks in advance,

  3. Reda Makhchan,

    Can you file a bug against the Flex SDK at and include your source code that works in the Flex SDK 3.0 but not in 3.1 or 3.2?
    Also, if you post the bug number here, a few of us can vote/subscribe to the issue.


  4. Peter,

    Do you happen to know why the nightly builds do not include any of the charting components? We use flex charts but would like to upgrade to new versions of the sdk, however, using the ones on the open source site won’t compile due to the missing charts. When you download flex builder 3.0, it comes with the charts embedded in the sdk.


  5. Brian,

    Good question. I believe this is the answer you are looking for, “Using Flex 3 Builds in Flex Builder”:

    If your application uses Flex Builder Professional features such as data visualization components or automated testing, you will need to copy those elements from the latest milestone SDK that came with Flex Builder into your newly downloaded SDK. The relevant files that you need to copy are:
    {sdkdir}/frameworks/rsls/datavisualization_3.0.0.477.* (or updated build numbers for later builds)
    {sdkdir}/fbpro (if you care about source)


  6. Hi Peter,

    Thanks for the response. With the nice feature Flex builder has for installing different SDKs, it would be nice if it is all bundled together. This makes it more challenging for upgrading to a new version for a large team of developers. Are there any downfalls to upgrading to a new version of rpc.swc without a matching version of the BlazeDS jars?


  7. Hi there,

    After I’ve installed and switched to SDK 3.1.0, I’ve lost my accessibility to flash library. (ex. when I write “import flash.” I see just “errors” as a suggestion nor events, nor display etc.) Is it normal? Can you help me how can I add the entirely flash lib in to my all projects like before.

    Thanks for now

  8. Trevor,
    Here is the reciept:
    Windows + Flex SDK + Flex Builder 3.0.194161
    To fix it:
    1) move /frameworks/libs/player/9/playerglobal.swc to /frameworks/libs/player/playerglobal.swc
    2) edit /frameworks/flex-config.xml


  9. Sorry, xml was cutted
    find node external-library-path in /frameworks/flex-config.xml
    and replace libs/player/{targetPlayerMajorVersion}/playerglobal.swc with libs/player/playerglobal.swc,
    that’s all

  10. Hi Peter,

    Nice article and blog.

    I am new to flex development.
    I am looking for information about fix to following bug:

    It is mentioned that fix will be release in Gumbo SDK.
    Is Gumbo SDK officially released?
    If yes, then why the bug is still open?

    Gurpreet Singh

  11. Gurpreet Singh,

    I’m not familiar with that bug, but I can answer your questions.
    1) Flex “Gumbo” is not officially released. It is still in alpha/beta, although you can download the nightly builds of the Flex Gumbo SDK from
    Flex Gumbo is currently scheduled to be released in the second half of 200, at least ccording to the following page:

    2) The bug is still open because it hasn’t been fixed yet, but it should be fixed before Flex Gumbo ships.


  12. Hi Peter, Thanks for your cool article!

    Here I met a problem when I try to instal Flex SDK(flex_sdk_4.0.0.5931). I followed your steps, step 1 to 4 was successful, but when I try the step 5, it says “Directory does not contain a Flex SDK” . It’s so pity that I spend many hours on it, but no result.

    May be it’s a fool question, but I really hope you can give me some ideas.

    Thanks in advance!

  13. sugar,

    It looks like 5931 is a bad build. I get the same error message when trying to add the SDK to Flex Builder. I did download and successfully use build 5900 though.

    Sorry, I’ll see if we can remove build 5931 from the list of nightly builds.


  14. Hi Peter:

    Thanks for all the great info you provide.

    I need to get started with Gumbo, and I need to use the data visualization and automation components. BTW, I own Flex Builder Professional.

    I’ve downloaded Gumbo and built a simple project successfully, but don’t know where to find the right libraries for data visualization and automation. In your response to Brian above, you mention copying these files from the latest milestone release, which works for me in 3.x.

    What should I do for 4.x? I’ve searched on the web for an answer, but so far have come up empty.


  15. Hey,
    nice blog, really!
    Is there an option or a compiler setting to hide the embed file in the release build? In fact I would like have just one big file instead of having a couple of files and img-directories!


  16. Hi Peter,
    i want to add air 2.5 sdk for android in FB4.
    i use these steps as per you define above, but when i compile project by selecting Air 2.5 sdk it shows an error message
    ‘An unknown sdk’.

    What can i do now?

  17. I have very basic question is there any setup script for Flex 4 or we need to use it using IDE as eclipse?

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