The news: Substack is testing its first structured sponsorship program, an opt-in beta that allows selected writers to insert paid brand placements directly into their newsletters, per a Substack note by co-founder Hamish McKenzie.

• Substack is formalizing what creators have long done on their own by offering built-in newsletter sponsorships.
• The beta is strictly opt-in, applies only to newsletters, and keeps creators in control; Substack won’t take a revenue share during testing.
• Rather than building a programmatic system, the platform is pairing a small group of writers with brands familiar with Substack’s audience.
• The shift reflects creator demand for easier monetization and Substack’s need to generate revenues from its large base of free readers.

Why it matters: Substack has grown its audience sharply despite limited advertiser adoption.

• US unique visitors nearly doubled from 6.3 million in May 2024 to almost 14 million by May 2025, showing meaningful top-funnel interest.
• Yet it is barely present in creator marketing today. Only 5% of brand marketers and 13% of agency marketers use Substack as a creator channel, and less than 1% cite it as their top ROI platform, according to CreatorIQ data.
• This gap between rising traffic and minimal marketer investment highlights why creators have pushed the platform to offer sponsorship tools that can monetize large free audiences.

The challenge: But engagement patterns reveal a difficult road ahead. Minutes-per-visit fluctuate dramatically, peaking at 4.4 minutes in December 2024 but falling below 1.5 minutes for much of 2025. Substack is attracting curiosity, but isn’t yet a habit.

• Sponsorships give Substack a way to turn growing reach into revenues without compromising its subscription-led identity. And by avoiding programmatic ads, it positions itself as the home for higher-touch, editorially coherent brand storytelling that avoids interrupting users.
• For creators, the beta is an opportunity to turn free readership into income without eroding trust or relying on off-platform deal-making.

Key takeaway for marketers: Substack is not a performance channel today, but the sponsorship beta signals a shift toward more structured, premium newsletter advertising. Brands that rely on depth, thought leadership, or niche expertise may find early-mover advantages.

• Expect a market where creator newsletters function as high-intent extensions of influencer campaigns—independent of social feeds but aligned with the same voices.
• Because Substack’s audience is growing faster than its engagement, marketers should pilot sponsorships as upper-funnel or mid-funnel opportunities rather than expecting social-style frequency or reach.
• The absence of programmatic inventory means placements will be handcrafted, context-rich, and tied closely to creator identity—an advantage for brands seeking trust over scale.
• If the pilot succeeds, Substack could evolve into a more substantive part of creator-marketing budgets, especially for categories that benefit from long-form persuasion: finance, B2B, wellness, education, and high-consideration consumer goods.