Twitter’s already building a competitor to the hot social audio app Clubhouse, but apparently, it’s discussed outright acquiring the company, too. Bloomberg reports today that Twitter held discussions with Clubhouse about purchasing the app for around $4 billion.

These conversations have reportedly stalled, and it’s unclear why. It’s also unclear whether Twitter or Clubhouse approached the other first, which could speak to how either platform is feeling about the competition in the social audio space. Bloomberg also reported yesterday that Clubhouse is now looking to raise money at a $4 billion valuation; it’s possible that number came out of these Twitter discussions, or that Clubhouse is shopping that figure around.

Clubhouse launched last year and popularized the idea of hosting live audio conversations. Celebrities, tech CEOs, and regular folks have since tuned in and hosted rooms. More than 10 million people have reportedly downloaded the app, which is currently invite-only and iOS-only.

The app also faces lots of competitors, including Facebook, Twitter, Discord, LinkedIn, and Slack, among others. These other platforms already come with built-in user bases of millions of people, as well as fully built web, iOS, and Android apps. Still, Clubhouse is rapidly trying to innovate. It’s staffed up in recent months and hired an engineer to build its Android app. It also, this week, launched tipping within the app as a way for creators to make money. (It says it won’t be taking a cut of that revenue.)

For its part, Twitter Spaces has already launched on both iOS and Android. The company also plans to launch a web version and to open hosting abilities up to all users this month. Why Twitter would want to acquire Clubhouse doesn’t totally make sense, unless it simply wanted to wipe the competition out and gain its dedicated user base and buzzy name. Either way, Clubhouse and Twitter now will both continue to face each other in the journey to dominate social audio.