How do I poll for new and changed Hacker News content?

Use GET /v1/hackernews/maxitem for the current high-water maxItemId to catch brand-new ids, and GET /v1/hackernews/updates for changedItemIds/changedUsernames to catch edits to existing items and profiles. Neither returns full bodies — hydrate the ids you care about with /items/{id}, /stories/{id}, or /users/{username} after filtering.