The singer, 32, was reported to have splashed $US1 million ($A1.4 million) on his 37-year-old actress partner's new bling after apparently proposing to her.
Kravitz, known for roles in The Batman and Big Little Lies and as the director of Blink Twice, sparked speculation she and Styles have secretly got engaged after she was spotted in New York City on 27 April wearing what experts say was a massive oval-cut diamond on her wedding finger, which they have estimated may have cost up to $US1 million ($A1.4 million).
Reports have described Styles' reported proposal as "traditional and romantic", with insiders claiming Kravitz accepted "immediately".
A source has now told RadarOnline.com: "There is a sense this relationship has moved quickly into serious territory, and with that comes practical conversations - particularly around finances and long-term protection."
Another insider told the outlet: "Those close to Harry are advising caution. When assets and public profiles reach this level, a pre-nup is seen as a sensible step rather than a cynical one."
Styles rose to fame with One Direction before establishing a solo career with albums including Harry's House and acting roles such as Don't Worry Darling and is worth an estimated $US304 million ($A422 million).
His fortune dwarfs Kravitz's estimated net worth of $US15 million ($A21 million).
The pair have been linked since 2024, maintaining a largely private relationship despite frequent sightings in London, Rome and New York.
Insiders also told Radar Styles is "deeply" committed to his actress partner.
One source said: "He is entirely devoted – the kind of devotion where he would do anything to make the relationship work."
Another insider described Kravitz as "incredibly happy" and "emotionally invested" in her relationship with Styles.
They added: "She feels supported in a way that is steady and grounding."
Kravitz was previously married to Karl Glusman, with the pair separating after two years.
The actress was also engaged to Channing Tatum, before their split in October 2024.
At the time, a source said: "The split is amicable. They realised they're at different stages in life."
Another added: "They hadn't been aligned for some time and ultimately grew apart."
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