The trend: Newsletter platforms are becoming a central hub for independent creators, brands, and journalists looking to own audience relationships rather than rent reach from social feeds. Substack, Beehiiv, and Mailchimp are all benefiting from this shift, though Substack is pushing hardest beyond email.

• Substack is testing its first structured sponsorship program, allowing selected writers to place paid brand messages directly into newsletters. The opt-in beta keeps creators in control and, for now, does not take a cut. The goal is to monetize large, free audiences without resorting to programmatic ads.
• That move comes as Substack’s traffic is surging; US unique visitors nearly doubled YoY by mid-2025, per Comscore, though marketer adoption remains limited. According to CreatorIQ, only 5% of brands report commonly using Substack for creator marketing.