Mucking around with the format parameter on a siteinfo call I got this with "action=query&meta=siteinfo&format=wddx" This was just now, around 0220 GMT, September 29, and the site is English Wikipedia. <?xml version=\"1.0\"?> <wddxPacket version=\"1.0\"> <header/> <data> <struct> <var name=\"error\"> <struct> <var name=\"code\"> <string>internal_api_error_MWException</string> </var> <var name=\"info\"> <string>Exception Caught: Internal error in ApiFormatWddx::slowWddxPrinter: Unknown type boolean</string> </var> <var name=\"*\"> <string>#0 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiBase.php(913): wfDebugDieBacktrace('Internal error ...')#1 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiFormatWddx.php(109): ApiBase::dieDebug('ApiFormatWddx::...', 'Unknown type bo...')#2 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiFormatWddx.php(95): ApiFormatWddx-&gt;slowWddxPrinter(false, 16)#3 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiFormatWddx.php(95): ApiFormatWddx-&gt;slowWddxPrinter(Array, 12)#4 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiFormatWddx.php(95): ApiFormatWddx-&gt;slowWddxPrinter(Array, 8)#5 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiFormatWddx.php(62): ApiFormatWddx-&gt;slowWddxPrinter(Array, 4)#6 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiMain.php(454): ApiFormatWddx-&gt;execute()#7 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiMain.php(434): ApiMain-&gt;printResult(false)#8 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiMain.php(248): ApiMain-&gt;executeAction()#9 /usr/local/apache/common-local/wmf-deployment/includes/api/ApiMain.php(232): ApiMain-&gt;executeActionWithErrorHandling()#10 /usr/local/apache/common-local/wmf-deployment/api.php(116): ApiMain-&gt;execute()#11 /usr/local/apache/common-local/live-1.5/api.php(3): require('/usr/local/apac...')#12 {main}</string> </var> </struct> </var> </struct> </data> </wddxPacket>