API 1.3 and ArcGIS 10.1?

[AdrianaCalleja]

I have developed some of applications on Flex 3 using API 1.3, now I'm going to migrate from ArcGIS 10 to ArcGIS 10.1 , so I need to know if it is probable that I will have trouble with some classes or functions included in the older API. 

Should I migrate my applications to API 3.3?

Thanks in advance,

Adriana C

[BjornSvensson]

I have developed some of applications on Flex 3 using API 1.3, now I'm going to migrate from ArcGIS 10 to ArcGIS 10.1 , so I need to know if it is probable that I will have trouble with some classes or functions included in the older API. 

I think that it will probably work fine -  using 1.3 API and 10.1 server.  See http://forums.arcgis.com/threads/72880-Can-Flex-Viewer-1.x-access-ArcGIS-Server-10.1

Should I migrate my applications to API 3.3?

While you don't need to, it might be a good idea. Version 1.x is no longer supported by Esri and most people on the forum are using version 3.x.  If you are just planning to change a URL to point to the new server, staying with 1.x might make sense. But otherwise, my recommendation would be to go with the latest API.
http://support.esri.com/en/content/productlifecycles
http://downloads.esri.com/support/product%20life%20cycle/online_gis/ArcGISWebMappingAPIs_PLC.pdf