SLI, Crossfire, need any special API to take advantage of

A coworker and myself are in a disagreement over whether games or apps can take advantage of SLI or Crossfire tech.

He says the program/software/game must be specifically written to see any speed increase out of SLI.

I disagree. I say the OS sees the SLI cards as just one card and displays it accordingly. He says that a special API or code has to be written to take advantage of the technology of dual/quad cards. He says it won't be able to natively take advantage of the tech till Direct X 10.

Who is right?

Any links to support what I'm discussing here?

Thanks in advance.