Agencies and brands suddenly have plenty of questions for Siri, which Apple is expected to extend from the iPhone to a new home-assistant device at its conference for developers next week.

Marketers and publishers are eager to see where they could fit into the device, but right now all they know is the world of Amazon and Google's assistants, where they've accumulated plenty of experience developing programs to answer consumers' commands.

Apple is late to the party. It also traditionally maintains tighter control over its ecosystem than its rivals.

"Amazon and Google have allowed broad third-party support, but brands may want to temper their expectations for any Siri additions," said Jon Reiling, AKQA's head of emerging technology for Atlanta and Washington, D.C., in an e-mail. "If their previous implementation of third-party Siri integration is anything to go by, Apple's concern for multilingual support, privacy and user experience means that they will remain gatekeepers for many elements of the user interaction."

So far, brands have taken most to Amazon, because its Alexa controls 70% of the voice-enabled speaker market in the U.S., according to eMarketer.

Alexa can take voice commands to order a Lyft, send a text message through AT&T, reserve a table through OpenTable and play videos from Amazon's library. Brands have the potential to score big when they become the go-to habit in a voice-assisted service.

"We've built prototypes for brands on Alexa and are working on one for Google Assistant," Azher Ahmed, exec VP-director of digital at DDB Chicago, said in an e-mail. The agency's emphasis is on services that naturally make sense for the way people use assistants and offer some kind of value, he said, as opposed to gimmicks designed just to force a brand's way onto a cool new platform.

Ahmed declined to identify the brands for which DDB is developing home-assistant apps.

Apple's Siri speaker will likely feature the "usual spit and polish" one expects from the hardware maker, Reiling said. Reports have indicated that the speaker will offer sound quality above Amazon and Google's devices.

Still, Siri does not have a reputation as the smartest smart assistant, and both Google and Amazon have superior machine learning technology. "Siri must differentiate in broad ways, beyond hardware," Reiling said. "The assistant is too quick to frustrate and too easy of a punchline."

Third-party developers could be the key to Apple's home-controlling devices, and it will look to dominate like it has with its app store, which has been the most innovative and lucrative. On Thursday, Apple said the App Store generated $70 billion for third-party developers since it first opened.

There will be room for that base of developers to build for Siri in the home. "If Apple releases this platform in the same way they released their watch and the iMessage platform, a native app developer will be able to simply build an extension for their app," Christian Brucculeri, CEO of Snaps, an Apple iPhone developer, said in an e-mail. "This would make sense as it'll allow Apple to leverage its massive installed app base to populate its speaker with experiences with the least amount of friction for consumers and developers."

But Apple often prefers its own services for music and other forms of media. That could make it hard, if not impossible, for Spotify and others to integrate with Siri in the home. Apple, of course, has Apple Music.