Get all posts without pagination

Yes, but you’ll have to be authenticated. Unauthenticated requests to the API will return the number of posts defined in the Settings > Reading section of the WP-Admin.

After you’re authenticated, you can make a query like so:

https://example.com/wp-json/posts?filter[posts_per_page]=-1

to get all of the posts. Also note that this may depend on your server’s capabilities, because loading thousands of posts might cause the server to run out of memory and thus error out.