Update, October 2026: The full HSK 3.0 exam specification is now out: the exam syllabus (November 2025) and the official sample papers (September 2026). Under the syllabus, Band 3 covers 1,000 words cumulatively, not about 2,245 (that is the 2021 standard figure), and Band 6 covers 5,400. HSK 3.0 launches officially with the December 13, 2026 sitting; see HSK 3.0 starts December 13, 2026.
HSK 3.0 is the largest overhaul of the HSK exam in over a decade. Short answer if you are deciding what to study: learn the HSK 3.0 vocabulary, while the band 1–6 exam format keeps using the version currently in use until the full spec is published.