I note that some people in my feed are able to make posts that seem to exceed the 500-character limit I face.

Is this a client-based option? Something controlled by the #mastodon instance one is on, or am I following accounts from other parts of the #fediverse (like blogging platforms) without realizing it?

Because... I'd love to make the occasional longer-form post... without it being broken up in to self-replies.