From @dildog:

Click 'Tweet' in the web ui

F12 Remove 'disable' on the tweet button

Click it, and go to 'network', right click on the request and copy as cURL

Then, add &weighted_character_count=true as a param to the end of the url

Then, resubmit the tweet with curl. — Rob Graham٩(●̮̮̃●̃) (@ErrataRob) September 27, 2017

User @ErrataRob posted one of the techniques (via @dildog), which involves meddling with the Chrome browser. As you can tell from the thread above, this method requires a bit of legwork. But, there is an easier way.

Here's a quick TamperMonkey script that force enables 280 character tweets in the Twitter web client.https://t.co/uUhW0CKekS — Prof. 9 (@Prof9) September 27, 2017

Twitter user @prof9 tweeted a link to a Tampermonkey script for Chrome that's much easier to set up, and offers the same result: Longer tweets. To get it working, first install Tampermonkey, and then head to this Github repository and click the raw button to install the script. Be sure to enable it in Tampermonkey, and then hit up Twitter.com and tweet away. All the current methods floating around are related to the Twitter web client. And, you'll probably have to be quick, as Twitter is likely scrambling to find a fix.