Threads is completely free while Twitter blue subscription costs about Rs 650 per month. Note that the basic Twitter version is free.
Threads is currently only available on mobile and does not have a web version as of now. Twitter is available both on mobile and web.
Threads allows you to post upto 500 characters while Twitter keeps upto 280 character for a basic version.
Those who are verified on Instagram will automatically be verified on Threads as well. In Twitter, you have to purchase the monthly subscription to get the blue tick.
Threads allows you to post website links, videos, Gifs and images along with carousels. The carousels, sliding photos upto 10, feature is missing on Twitter.
Engagement
Threads user can sign-up via their Instagram ID while Twitter user has to sign-up in a usual way
Threads neither has a discover feature nor a search feature at this time. Twitter provides more curated and choice-based content.
Threads doesn’t allow to message directly to others. Twitter has the feature.