If you collect these free V5 exclusives now (Haruka, Eristence, the Cross-lingual modes), they will likely be forward-compatible with V6.

Historically, "free" in the Vocaloid world usually refers to one of three things:

The release of VOCALOID5 by Yamaha Corporation in 2018 marked a significant paradigm shift in vocal synthesis technology, moving towards a sleeker interface and AI-assisted vocal phrasing. However, the high cost of entry and fragmented marketing strategies led to a surge in the circulation of "free exclusive" voicebanks on unauthorized platforms. This paper examines the phenomenon of pirated VOCALOID5 voicebanks, specifically analyzing the technical reality behind claims of "exclusivity," the security risks inherent in cracked software, and the ethical implications for the Vocaloid ecosystem. The study concludes that while unauthorized distributions lower the barrier to entry, they actively degrade the user experience through security vulnerabilities and undermine the financial viability of the voice providers and software developers.

These aren’t exclusive (some are sold separately as V4 banks), but they come bundled. If you upgrade from V4 to V5, you keep your existing banks + get these.