The announcement comes less than one week after Apple Computer began offering its new operating system in stores. The long-anticipated and much-delayed release is the first major overhaul of the Mac OS since its 1984 introduction.
The beta, or test, version of AIM 4.5 does not have any new features beyond compatibility with OS X.
"We wanted to make sure that our AIM users who are using OS X on their computers have a version of AIM that they can use," said Jane Lennon, an AOL spokeswoman.
The AOL Time Warner subsidiary did not offer any time frame for when the final version of 4.5 will be available. "As with any new product we have in development, we will be testing it in every way possible," Lennon said.
Instant messaging has become a highly popular program, with most big Internet companies offering services. AOL's AIM service, once the leader in the IM market, has lost its dominance in recent months to Microsoft.
A recent report from Jupiter Media Metrix showed Microsoft's MSN Messenger with 29.5 million members compared with 29.1 million members for AIM.