The definitive notification stack altitude map

Search “best push notification service” and you’ll find listicles ranking Firebase alongside BzBraze. OSOneSignal next to CCustomer.io. Expo Push in the same table as Intercom.

These articles aren’t wrong about the individual tools. They’re wrong about the category. They compare tools that solve fundamentally different problems at fundamentally different layers of the stack.

The result: founders pick a marketing automation platform when they need a delivery pipe. CTOs evaluate notification infrastructure when they actually need a campaign tool. Teams build custom orchestration logic on top of tools that already include it — or worse, try to use a push delivery service as a preference management system.

I ran into this myself while building Tortie — a couple expense tracker in React Native. When I searched for “the right push notification service,” every comparison article mixed altitude levels. Firebase (a delivery protocol) was ranked against OSOneSignal (a campaign platform) was ranked against KKnock (notification infrastructure). The comparison was useless because the tools aren’t solving the same problem.

So I mapped the stack. Five altitudes, from raw cloud infrastructure at the bottom to full customer engagement platforms at the top. Each altitude has different tools, different buyers, different cost structures, and different engineering requirements.

This is that map.

Every push notification you’ve ever received — regardless of which service sent it — flows through the same two pipes at the bottom: Apple’s APNs and Google’s FCM. Everything above those pipes is a question of how much you want to build yourself versus how much you want to buy.

The five altitudes, from bottom to top:

5 CDP / Full Communications Platform CCustomer.io BzBraze Intercom 4 Notification Infrastructure KKnock NvNovu CoCourier 3 Push Service + Engagement OSOneSignal PwPushwoosh 2 Push Delivery Layer FCFCM APAPNs Expo 1 Raw Infrastructure SNSAmazon SNS Google Pub/Sub

SNSAmazon SNS, Google Pub/Sub

Operating at altitude 1 means your engineering team takes full ownership of everything above the cloud messaging bus: routing logic, user preference management, template rendering, analytics, retry logic, token lifecycle management, segmentation, rate limiting, and A/B testing.

Estimated engineering investment before the first user-facing notification: 6–18 months.

Who operates here Sony PlayStation Network (123 million MAUs, using SNS+SQS for hundreds of thousands of requests per second), Netflix, Meta. Teams with dedicated notification infrastructure engineers. Teams where third-party platforms become cost-prohibitive or architecturally limiting at their scale.

For the vast majority of products — including most venture-backed startups — altitude 1 is overkill. You’d be building a notification platform from scratch instead of building your product.

FCFCM, APAPNs, Expo Push

These are the two literal pipes through which every push notification flows — regardless of what platform, SDK, or service you use above them. OSOneSignal uses FCM and APNs. BzBraze uses FCM and APNs. SNSAmazon SNS uses FCM and APNs. They’re the foundation.

Key insight — neither FCM nor APNs has any concept of users, preferences, campaigns, or analytics. They only know device tokens and JSON payloads.

For React Native / Expo teams, Expo Push is the path of least resistance. Zero config (EAS handles credentials), free, handles both platforms through a unified API. You send a single HTTPS POST to Expo’s endpoint, and Expo routes to the appropriate platform.

	FCFCM	APAPNs	Expo Push
Cost	Free	Free ($99/yr Apple Dev Program)	Free
Rate limit	600K msg/min/project	Not published	600/sec/project
Platform	Android native, iOS via APNs proxy	iOS/macOS/watchOS only	Both (abstraction over FCM + APNs)
Message size	4,096 bytes	4,096 bytes (standard)	4,096 bytes
Delivery confirmation	Yes (delivery receipts)	No (best-effort, no receipts)	Partial (receipt = handed to FCM/APNs, not device)
Broadcasting	Yes (FCM Topics — one API call)	N/A	No (must enumerate every token)

OSOneSignal, PwPushwoosh

This is where most teams land first. Self-service access. Developers can be sending push notifications within minutes, often free. Segmentation, scheduling, A/B testing, analytics — without building the infrastructure.

OSOneSignal is the de facto default: 1 in 5 mobile apps released in 2023 had the OneSignal SDK installed. 12 billion messages sent daily. The free tier offers unlimited mobile push with unlimited subscribers — confirmed as of March 2026.

PwPushwoosh is the less-known alternative with some meaningful advantages: unlimited journeys on every tier (OneSignal caps at 1–3), direct event triggers (OneSignal requires tag workarounds), frequency capping included for free (OneSignal gates this to Enterprise), and WhatsApp support (OneSignal doesn’t offer it).

Here’s where most comparison articles fall apart. They rank OSOneSignal and KKnock in the same table, compare features side by side, and declare a winner. But they’re asking the wrong question.

The right question isn’t “which tool has more features?” It’s “what is a notification in your product?”

If notifications are a delivery mechanism — fire-and-forget alerts that tell users something happened — you’re at altitude 3. OneSignal, Pushwoosh. Campaign platforms with push delivery, segmentation, and analytics. The person configuring them might be a developer, a product manager, or a marketer.

If notifications are a product feature — a persistent in-app feed, a workflow engine that orchestrates multi-step sequences, user-controlled preferences for which channels receive which notification types — you’re at altitude 4. Knock, Novu, Courier. Notification infrastructure that engineers own and build into the product’s architecture.

Three markers that mean you need altitude 4

1. In-app notification inbox/feed — a persistent, real-time notification center embedded in your product. Not just a transient push alert. A place users go to see what’s happened.
2. Workflow engine — conditional, multi-step orchestration. If a user triggers X, send push now. If not read in 1 hour, send email. If no action in 24 hours, send SMS. This is beyond what a “journey” in OneSignal can do.
3. Preference management — user-level controls over which channels receive which notification types. “Notify me about comments via push, but marketing updates only by email.” Architectural, not just a settings toggle.

At altitude 3, a notification is something you send. At altitude 4, a notification is something you build.

The ownership shift is just as important: at altitude 4, a pull request is how you change a notification workflow. At altitude 5, a campaign draft is how you change it.

KKnock, NvNovu, CoCourier

This is the altitude most comparison content doesn’t know exists. Analysis of nine existing comparison articles found that the notification infrastructure category is invisible in roughly 80% of content. Articles that do cover it don’t map it against the layers above and below.

These three tools share a common architecture: they’re orchestration layers above delivery providers. None of them deliver email, SMS, or push directly. They route through your configured providers — SSendGrid for email, Twilio for SMS, FCM for push. They add the intelligence layer: workflow logic, preference management, batching, throttling, and in-app notification feeds.

The React Native verdict

For React Native / Expo teams specifically, the SDK story matters:

CoCourier wins for fastest path to production-ready inbox UI. CourierInboxView is a pre-built, drop-in notification inbox for React Native — unique advantage. Neither Knock nor Novu offers pre-built RN UI components.

KKnock wins for strongest Expo push integration. The KnockExpoPushNotificationProvider wrapper with useExpoPushNotifications hook provides automatic push token registration and engagement tracking — first-class treatment.

NvNovu wins for cost and flexibility. Self-hosted option on Docker, code-first workflow definition via @novu/framework TypeScript SDK, and the strongest open-source community (38.3K GitHub stars, 446 contributors).

All three provide headless hooks for in-app feeds in React Native — but only Courier gives you a pre-built visual component out of the box.

CCustomer.io, BzBraze, Intercom

At altitude 5, notifications are one channel within a broader engagement strategy. The person configuring notifications isn’t an engineer — it’s a marketer, a growth lead, or a support manager. The question shifts from “how do we build notification logic?” to “how do we orchestrate customer communications across all channels?”

CCustomer.io is the mid-market entry point. Starting at $100/month for 5,000 profiles and 1M emails/month. Behavioral messaging with event-triggered campaigns, lifecycle workflows, and a Transactional API that handles password resets, receipts, and OTPs. Hit an estimated $100M ARR in September 2025. Startup program: 12 months free for companies that raised under $10M.

BzBraze is the enterprise tier. ~$593M revenue (FY2025), publicly traded (NASDAQ: BRZE). Real-time stream processing architecture (not batch). Canvas workflow builder with up to 200 steps. AI Decisioning Studio (powered by OfferFit acquisition) replaces A/B testing with autonomous personalization. Named a Leader in 2025 Gartner Magic Quadrant for Multichannel Marketing Hubs — third consecutive year. Minimum ~$60K/year. Kayo Sports saw a 14% subscription increase and 105% cross-sell increase using BrazeAI.

Intercom has pivoted decisively to AI-first customer service. Fin AI Agent is the centerpiece. Push notifications in Intercom are an add-on to a support product ($99/month Proactive Support Plus add-on) — not a growth tool. Use Intercom for notifications only when your primary use case is customer support and notifications are a side-channel to keep support conversations alive.

Every player is adding features from adjacent altitudes. OSOneSignal added Journeys and behavioral Events (climbing toward altitude 5). KKnock added Broadcasts and Guides (reaching toward altitude 5). CCustomer.io added a Transactional API (reaching down to altitude 4).

The marketing language is converging. The architecture isn’t.

A company can “send a campaign” in Knock and “send a transactional” in Customer.io, but the underlying engineering model, data model, and organizational ownership remain fundamentally different. OneSignal’s Journeys are drag-and-drop workflows operated by marketers. Knock’s workflows are code-reviewed orchestration logic operated by engineers. Customer.io’s Transactional API is a single-message-per-call endpoint that lacks Knock’s batching, throttling, and digest primitives.

Convergence makes sense within an altitude — consolidating from three email providers to one. It rarely makes sense across altitudes — using one tool for both infrastructure and campaigns creates architectural coupling that limits both.

The altitude that’s right for you depends on three things: what notifications mean in your product, who owns them in your organization, and where you are in your growth.

I analyzed nine existing comparison articles while researching this topic. Every one commits the same structural error: comparing tools across altitudes as if they’re solving the same problem.

A typical article table looks like: OneSignal vs Knock vs Braze vs Firebase vs Pushwoosh — all ranked on the same criteria. But Firebase is a delivery protocol (altitude 2). OneSignal is a campaign platform (altitude 3). Knock is notification infrastructure (altitude 4). Braze is an enterprise engagement suite (altitude 5). Comparing them in one table is comparing SMTP to Mailchimp.

Six gaps the altitude map fills

1. The decision framework gap — no article answers “what altitude do I need?” before “which tool at that altitude?”
2. The stack composition gap — no article discusses that you might need tools at multiple altitudes simultaneously.
3. The migration arc gap — no article discusses the natural progression from lower to higher altitudes as complexity grows.
4. The ownership question gap — no article asks “who in your organization owns notifications?” — which is the most important question for choosing altitude.
5. The architectural implication gap — no article explains that choosing a tool at the wrong altitude creates technical debt.
6. The consolidation question — when to run one tool per altitude vs. consolidate. Within-altitude consolidation makes sense. Cross-altitude consolidation creates coupling.

Ready to choose within an altitude? These deep-dives compare tools head-to-head:

Altitude 3 vs. 4 boundary

OneSignal vs Knock — mobile notification infrastructure compared

Which notification infrastructure for your mobile app? Decision framework and pricing.

OS

K

Coming soon

Altitude 2 → 3 transition

Expo Push vs OneSignal — when to graduate from built-in push

For React Native / Expo teams: when to graduate from Expo’s built-in push to a platform.

OS

Coming soon

Altitude 4 head-to-head

Knock vs Novu vs Courier — notification infrastructure compared

Three notification infrastructure platforms compared on architecture, pricing, and DX.

K

Nv

Co

Coming soon

Email delivery layer

Transactional Email: Loops vs Resend vs Postmark vs SendGrid

The email delivery layer — choosing a provider for receipts, resets, and operational messages.

S

Coming soon

Altitude 5

Customer.io vs Braze vs Intercom — enterprise engagement compared

Enterprise engagement platforms for marketing-led teams at scale.

C

Bz

Coming soon