Substack doesn’t talk about its algorithm the way most platforms do. There’s no transparency report, no public documentation of ranking factors, no equivalent of Google’s Search Central blog. What there is, instead, is a pattern — visible in the data, confirmed by the platform’s own head of machine learning, and increasingly obvious to anyone paying attention: Substack’s discovery system structurally rewards writers who do their work inside the ecosystem. Not just their writing. Their socialising, their networking, their promotion, and their audience-building.
That’s not a bug. It’s the business model. And if you’re a blogger or publisher evaluating whether Substack deserves a place in your strategy, understanding this dynamic matters more than any feature comparison.
How discovery actually works now
In late 2025, Substack’s head of data, Mike Cohen, published a technical deep-dive on how the platform’s recommendation system operates. The key shift: Substack moved from a static profile-matching model to what Cohen described as sequential modelling. Instead of asking “what does this reader usually like?” the algorithm now asks “what would be the natural next step for this reader right now?”
That’s a meaningful distinction. It means the system tracks reading journeys in real time — what someone read, what they restacked, what they engaged with in Notes — and uses that behavioural chain to decide what to surface next. Cohen was explicit that the system works because Substack controls the full interaction lifecycle. Sharing, restacking, and replying all happen on the platform, giving the algorithm a complete picture of behaviour that external platforms simply can’t provide.
The practical implication is clear: writers who generate engagement inside Substack — through Notes, comments, restacks, and recommendations — give the algorithm more signal to work with. Writers who publish on Substack but do their audience-building on LinkedIn or Twitter are handing the system less data. Less data means less discovery.
The numbers confirm the pattern
Substack reports that its network drives 25% of all paid subscriptions across the platform. Recommendations alone account for 50% of all new free subscriptions. More than 25% of total subscriptions now originate from the Substack app itself. And in late 2025, the company shared that 32 million new subscribers came from within the app over just three months — not from external traffic, not from social media, but from readers discovering writers inside the ecosystem.
Readers already in the Substack system are 3x more likely to convert to a paid subscription than someone arriving from outside, because their credit card is already on file. One-click checkout versus a cold landing page is a conversion advantage that compounds at scale.
For writers who participate actively in the ecosystem — posting Notes daily, recommending other publications, restacking, engaging in comment threads — the discovery engine responds. One creator reported gaining 10+ subscribers per day from Notes alone. Another tracked that 80% of new subscribers were coming from within Substack, not from the external platforms where they’d been spending most of their promotional energy.
The message from the data is consistent: the more of your publishing activity happens inside Substack’s walls, the more the platform’s discovery machinery works in your favour.
This is a deliberate design choice, not an accident
It’s worth understanding why Substack built it this way, because the incentive structure explains the behaviour the algorithm rewards.
Substack makes money through a 10% commission on paid subscriptions. It doesn’t sell ads (at least not yet — the $100 million Series C in mid-2025 has prompted speculation). It doesn’t monetise attention through time-on-platform metrics. Its revenue is directly tied to the number of paid subscriptions that exist on the platform.
That means Substack’s algorithmic incentive is to match readers with writers they’ll pay for. Not writers who’ll generate engagement for engagement’s sake — writers who’ll generate conversions. And the best predictor of conversion is ecosystem-native behaviour: a reader who subscribes to one publication through a recommendation, engages with related Notes, discovers a second publication, and eventually upgrades to paid.
Every step of that journey happens inside Substack. The algorithm can track it, learn from it, and use it to improve the next recommendation. When a writer publishes a post and then promotes it through a LinkedIn thread, the algorithm sees the post but not the promotional context. When that same writer posts a Note linking to their piece, restacks someone else’s related work, and replies to comments, the algorithm gets a rich signal chain it can act on.
This is why Substack’s discovery system favours ecosystem participation. It’s not punishing writers who promote externally. It’s simply unable to see that activity — and what it can’t see, it can’t reward.
The strategic tension bloggers need to understand
For independent publishers and bloggers, this creates a genuine strategic question. Substack’s discovery engine is powerful — arguably more effective for audience growth than any newsletter platform’s organic distribution. But it’s powerful because it’s closed. The more you invest in Substack’s ecosystem, the more Substack’s ecosystem invests in you. The less you invest elsewhere.
That’s the trade-off. And it’s the same trade-off that every platform with network effects eventually presents. YouTube rewards creators who keep viewers on YouTube. Instagram rewards content that keeps users in the app. Substack rewards writers who keep readers inside Substack.
The difference — and this matters — is that Substack lets you export your subscriber list. You own the email addresses. If you decide to leave, you can take your audience with you. That’s a genuine distinction from platforms where your followers are rented. But the discovery advantage doesn’t travel with you. The recommendations, the Notes reach, the algorithmic placement — all of that stays behind.
For bloggers who already have established audiences and diverse traffic sources, Substack can function as one channel among several. Publish there, cross-promote, benefit from the discovery layer without depending on it entirely. But for writers who go all-in on Substack as their primary platform, the ecosystem rewards are real — and so is the dependency they create.
What this means for your newsletter strategy
If you’re on Substack or considering it, the strategic takeaway is straightforward. The platform’s discovery system is optimised for writers who treat Substack as a community, not just a publishing tool. Posting Notes consistently, recommending other publications genuinely, restacking and replying, building relationships with other writers in your niche — these aren’t optional extras. They’re the inputs the algorithm needs to surface your work to new readers.
But pair that ecosystem investment with an export strategy. Build your email list through Substack’s tools, but know where you’d take that list if you needed to. Maintain at least one external channel — a blog, a presence on another platform — so that your entire publishing operation doesn’t live inside a system whose rules can change without your input.
The writers who’ll do best on Substack in 2026 and beyond are the ones who understand both sides of this equation: the discovery engine rewards ecosystem loyalty, and that reward is genuine. But loyalty to a platform is a strategy, not a principle. The moment the incentives shift — through advertising, algorithm changes, or pricing adjustments — you want the option to move. Substack gives you that option structurally. Make sure you’ve built the infrastructure to use it.
