"How the Substack Notes Algorithm Works" — Dickie Bush & Nicolas Cole

Why this is in the vault

Concrete, cited mechanics of how Substack Notes surfaces content to readers — directly relevant to Sanity Check's growth strategy if Ray moves it to or cross-posts on Substack.

⚠️ Sponsorship

Ship30for30 self-promo: the email is framed as proof of their "Write With AI" paid newsletter ($400K/year) and pivots at the end to a Substack Starter Kit + AI Writing Skool upsell. The algorithm content is real but exists to establish credibility for the pitch.

The core argument

The Notes algorithm is optimized for subscriber conversion, not scroll time. Substack earns 10% of paid subscriptions, so its incentives align with creator success rather than engagement addiction. Mike Cohen (Substack Head of ML) confirmed: "The goal is to get people to discover, subscribe, and ideally pay."

How the feed ranks Notes:

• Reader profile: location, language, subscriptions, followed writers, declared interests
• Engagement behavior: clicks, likes, restacks, comments
• The system converts these into a numerical match score against available content

2025 upgrade — sequential models: Substack moved from static preference snapshots to dynamic session modeling. If a reader clicks a productivity Note, the feed momentum-shifts and surfaces more productivity content in that same session. Your Note competes within the context of what that reader is interested in right now, not against everything on the platform.

Two structural signals:

1. Restacking and replying create recommendation bridges — audience overlap between publications gets traced, so interacting with a complementary writer can extend your reach to their subscribers.
2. Consistency beats virality — Substack's own data showed steady daily posting outperforms occasional viral spikes. The sequential model learns posting patterns; irregular cadence loses the model's attention.

Platform traction as of October 2025: The Substack app drove 32 million free and 500,000 paid subscriptions in 3 months, becoming the #1 subscriber source for publishers.

Mapping against Ray Data Co

Sanity Check is currently email-native (not on Substack). If Ray ever moves Sanity Check to Substack or runs a parallel Notes presence, these mechanics apply directly:

• Algorithm alignment is structural: Unlike X or LinkedIn, Substack Notes actively promotes subscriber conversion. Running Notes as a top-of-funnel for a paid newsletter is structurally favorable in a way other platforms aren't.
• Sequential models reward topical consistency: Sanity Check has a clear AI+data niche — staying in-niche on Notes would benefit from momentum surfacing within that topic cluster.
• Restack strategy = partnership leverage: Identifying 3-5 adjacent newsletters (AI tools, data strategy, founder operators) and restacking them regularly could build cross-audience bridges at zero cost.
• Daily cadence as algorithm signal: The consistency finding maps to Sanity Check's editorial discipline question — irregular posting hurts discoverability even if individual pieces are high-quality.

Related

• [[2026-01-27-ship30for30-substack-newsletter-guide]]
• [[2026-03-13-ship30for30-substack-growth-strategy]]
• [[2026-03-06-ship30for30-newsletter-as-engine]]
• [[2026-06-19-ship30for30-first-10-newsletters]]
• [[2026-04-03-curiosity-consistency-newsletter-growth]]