The register
The register lists Greenstone+ Ltd in London, London as a licensed sponsor on Skilled Worker, an entry that goes back to at least 2026. Its rating on the register is Worker (A rating).
At Companies House the business is Greenstone+ Limited (company number 05757600), a private limited company incorporated in 2006, 20 years ago. The registered office is at 5th Floor Crown House, 143-147 Regent Street, London, W1B 4NR, W1B 4NR. Its filed activity puts it in professional and technical services. It has traded under other names before, including Greenstone Carbon Management Limited.
What the licence tells a candidate is that the door is not locked. Whether it is open this month is a question for Greenstone+ Ltd's own careers page and the job boards, and the answer changes with the season and the order book.