Likely, WiMAX standards will never be completely finalized.  Other standards such as the cable DOCSIS (now in Version 3.0) have continued to evolve, even once a very mature level of performance was realized.  However, it has evolved more slowly.  WiMAX moved swiftly through several updates even before testing standards were defined and products began to be widely available.  The technology has evolved from the base 802.16 standard through several updates during the last few years including:
802.16a
802.16c
And finally 802.16d or 802.16-2004
All of which are primarily Fixed WiMAX standards. 

802.16e or Mobile WiMAX was finalized late in 2005.  This version is not backwards compatible with the 802.16-2004 fixed standard. 

A newer iteration of WiMAX called 802.16m that more specifically addresses numerous mobile capabilities and should considerably improve bandwidth throughput is in the works.  There is some consideration that this standard could incorporate the emerging LTE standard as well, however wireless industry politics may preclude this.