Mark Zuckerberg has tried for years to take on Twitter. Now he may finally have his best chance to deliver a knockout blow to the social network at a turbulent moment.

On Thursday, Meta is expected to launch Threads, which the company describes as a "text-based conversation app" and whose promotional screenshots resemble Twitter's layout.

Twitter, meanwhile, has been stuck in a days-long crisis of its own apparent making after it deliberately throttled users' ability to view tweets. The company claims the move is temporary and aimed at defeating automated bots and artificial intelligence companies that use Twitter data to train their algorithms.

Whatever the reason for Twitter's decision to make using its platform more difficult, the net result is that it's never been easier for users to switch away. The current crisis also comes after months of uncertainty about the platform's future, which has laid the groundwork for a growing list of Twitter alternatives.

Poised to benefit are rivals including Meta's Threads; the decentralized social network Mastodon, which according to its creator saw a spike in signups over the weekend; and Bluesky, backed by Twitter co-founder Jack Dorsey, which had to pause new signups on Saturday due to overwhelming interest.

Unlike Mastodon and Bluesky, however, Meta has enormous resources to throw at Threads, and a huge existing user base in Facebook and Instagram to which it can cross-promote its new app.

Meta has tried to muscle in on rivals before, with mixed success. Instagram's Stories feature, a Snapchat clone, quickly became more popular than Snapchat itself. Other standalone apps from the company such as Poke, Slingshot and Lifestage have each stumbled, however, in the face of a dominant defender and little demand from consumers for an alternative.

But Threads is launching at a time when its chief competitor — Twitter — has engaged in multiple acts of apparent self-sabotage and when much of its audience now seems up for grabs.

Twitter owner Elon Musk may sense the unique threat Meta poses to the company he bought for $44 billion. The Threads launch prompted some barbs from Musk directed at Meta and appeared to be the spark for a potential cage match between himself and Zuckerberg.

Twitter's terrible week

Under Musk, Twitter has stumbled through crisis after crisis, from mass layoffs that hit its content moderation teams to more frequent system outages to the rocky rollout of a controversial new verification system. Twitter's own investors have repeatedly marked down the company's estimated value since the acquisition.

But the events of the past week may ultimately do more to drive users away than almost anything else Musk has done to date.

On Friday, Twitter made tweets inaccessible to anyone who wasn't logged in, reducing the reach of the platform's content. Tweets that were once visible to anyone with a web browser suddenly were required to have an account to view the content.

Musk said the change was a "temporary emergency measure" in response to "data pillage" by third parties, and it now appears to have been reverted, but the move caught many users by surprise — and it was only the first of several jarring changes over the weekend.

On Saturday, Musk announced further "temporary limits" that restricted the number of tweets that users can view on any given day. Paid members of the company's Twitter Blue subscription service would be limited to reading 6,000 tweets a day, Musk said, while non-subscribers would be limited to reading 600 tweets a day. After a swift backlash by users, Musk was — twice — forced to increase the limits: first to 8,000 and 800 tweets a day respectively, and then to 10,000 and 1,000 tweets a day.

Twitter's newly appointed CEO, Linda Yaccarino, later defended the decision.

"When you have a mission like Twitter -- you need to make big moves to keep strengthening the platform," Yaccarino tweeted. In a blog post, the company said the current limits affect only a "small percentage" of users and that the impact to advertising has been "minimal."

Then, on Monday, Twitter announced that users will soon be required to pay to use Tweetdeck, a longtime free Twitter app beloved by professional users that allows them to view multiple Twitter feeds at once and to display custom search results or Twitter lists. The change will take effect in August and will require Tweetdeck users to be Twitter Blue subscribers to maintain access.

Can Twitter disappear?

For years, Twitter has been the go-to social platform for real-time news and commentary. What always allowed the company to punch above its weight was the presence of numerous celebrities, world leaders, businesspeople and other high-profile power users, along with the platform's openness and accessibility.

Twitter's success reflects an immutable law of social media: The more of your friends that are on a social network, the harder it tends to be to leave that network for another. Nobody wants to be the only person in a friend group using a new app by themselves.

But every so often, something big happens and a platform once thought to be essential or enduring goes extinct, or becomes a shadow of its former self, as users abandon it in droves for something else. Behind these sea-changes are usually two related phenomena.

The first is a shift in the critical mass of users that otherwise helps a platform retain its staying power, also known as "network effects." The second is a change in "switching costs," or the deterrent to users represented by the inconvenience, loss of social connections, or sometimes even the actual financial costs of switching platforms or providers.

It's rare to see these dynamics play out in real time, but the internet may now be reaching another one of those turning points.

What's happening with Twitter is that the company has sharply reduced users' switching costs. By restricting its own core functions and availability, Twitter has significantly lowered the barriers to trying a new app and increased the costs of trying to use Twitter the way it was before.

The more Twitter users head for the exits, the more its alternatives benefit from network effects.

Even if Twitter's changes are as temporary as the company claims, some damage is already done. On Sunday, Mastodon founder Eugen Rochko said the platform's active userbase rose by 110,000 in a single day, and by nearly 300,000 by the end of the weekend, reflecting higher usage by both new members and existing members alike. Bluesky reported system slowdowns as a result of "record-high traffic" and a "large influx" of new users.

Now, with Threads, Meta seems eager to capture some of the upside, too.