There's been concerns: Elon Musk has said Twitter is at risk of declaring bankruptcy, many engineering staff have been laid off, rumors of lurking technical debt that could bring down the site irrecoverably, landlords not being paid on-time, Twitter is being rebranded to X and a new domain is being set up, and likely more-to-come.
Resolves YES if twitter.com is accessible by web browser as of market close, and any new message is able to be posted to the site. Otherwise NO. This market does not resolve NA.
Temporary outages do not count, and if it's unclear whether an outage is temporary or permanent the market can be extended by up to 1 week before it will just resolve NO.
If twitter.com redirects to any other site(such as x.com) or subdomain, then the new domain is considered twitter.com as long as any publicly-available messaging service is available there. It's acceptable to require free or paid signups. I will attempt to use my existing Twitter account, but if it's banned or disabled due to lack of payment I will rely on credible reporting that there is still an active messaging service on the domain.