2. Orb

Orb (now acquired by Ayden) is a usage-based billing platform known for clean API design and billing-accuracy features like backfills and audit trails. It ingests raw events, defines metrics with SQL, and produces invoices that reflect contract terms and corrections without manual cleanup. 

If you’re evaluating Orb, you need to take into account that Adyen acquired Orb in an all-cash deal valued at $335 million, announced June 11 and closed July 1. 

With the stated goal of folding Orb into Adyen's billing-and-payments stack for enterprise merchants. That's worth weighing if you care about staying independent of a payments giant.

Core features:

• Real-time event ingestion with automatic deduplication.

• Usage metrics defined in SQL for flexible modeling.

• Tiered, volume, and package pricing with customer-specific rates.

• Invoicing that handles backfills, corrections, and contract terms.

• An audit trail of every pricing change and amendment.

Best for: infrastructure and API-first companies that want event-level control over metrics and invoicing accuracy. Where Orb keeps entitlement enforcement separate from billing, Flexprice ships usage, credits, entitlements, and cost tracking in one system. 

Flexprice vs Orb covers the open-source and multi-gateway differences.

Pricing: custom, based on billings and events. Orb stress-tests ingestion to 250,000+ events per second.

G2 rating: 5.0/5.

3. Metronome

Metronome (now acquired by Stripe) is a usage rating for AI and infrastructure companies, where a small error in usage math turns straight into a revenue error. 

It ingests large event streams, applies rating logic, and outputs clean billable usage that flows into a billing system for invoicing.

Metronome is now a Stripe product. Stripe acquired it for roughly $1 billion and closed the deal on January 14, 2026, which is a fairly direct admission that Stripe's own billing couldn't handle what AI-scale customers needed. 

I'll be honest, watching Stripe pay a billion dollars for the product that fixed its own billing gap is the clearest proof I've seen of how hard usage math gets at scale. 

Metronome uses aggregated metering, so re-aggregation is required when pricing logic changes. Flexprice runs on a raw-events model with no rate limits, which avoids that constraint.

Core features:

• High-throughput event ingestion built for billions of events.

• Usage rating and aggregation with configurable pricing logic.

• Contract and commitment management.

• Data-warehouse sync with Snowflake, BigQuery, and Redshift.

• Real-time usage alerts and reporting.

Best for: AI and infrastructure teams processing billions of events that want a dedicated rating layer. If you'd rather not lock into the Stripe ecosystem, Flexprice vs Metronome lays out the alternative.

Pricing: custom, enterprise-oriented.

G2 rating: not yet rated on G2.

4. Stripe Billing

Stripe Billing is the simplest place to start when usage is an input to invoicing rather than a control on your product. 

You send usage events, define pricing, and Stripe calculates charges at the end of each cycle. Limits and enforcement usually live in your own application code.

Stripe is a genuinely good default for simple models, and its documentation and payments footprint are hard to beat. 

Two caveats. Complex multi-dimensional pricing still needs heavy custom work, and Stripe now points AI usage-billing demand at Metronome, the separate product it bought for that exact gap. Users on review sites also report account holds, slow support, and rigid customization when pricing gets complicated.

Core features:

• Metered billing on API calls, seats, or custom meters.

• Tiered, volume, and hybrid pricing.

• Global payments, tax, and invoicing.

• Revenue recognition tied to billing data.

• Well-documented developer APIs and a large integration ecosystem.

Best for: API-first startups that want to launch usage billing quickly on a global payments backbone. For anything AI-native or multi-dimensional, Flexprice vs Stripe shows where it runs out of room.

Pricing: a flat 0.7% of billing volume (consolidated from two tiers in 2024), which includes 100M meter events a month, with larger volumes routed to sales.

G2 rating: 4.4/5

5. Lago

Lago is an open-source option and the closest peer to Flexprice, since both are OSS and both target developer-led teams. 

You send events like API calls or credits, and Lago aggregates them into billable metrics in real time, with self-hosted or cloud deployment for teams with compliance needs.

Here's the honest comparison, because it's checkable. Lago runs on Ruby and handles roughly 15,000 events per second, and several of its features sit behind the paid cloud plan. 

Flexprice runs on Go plus Kafka at 60,000+ events per second and ships every feature, including the customer portal and RBAC, in the open-source tier. 

I have real respect for Lago here, they helped prove open-source billing works, so this one usually comes down to raw throughput and how much sits behind the paywall. If open source is a hard requirement, these are the two to compare.

Core features:

• Event-based metering with real-time aggregation.

• Hybrid billing across usage, subscriptions, add-ons, and prepaid credits.

• End-of-period invoicing or prepaid credit burn-down.

• REST API and webhooks for every billing operation.

• Finance integrations with Stripe, tax, and accounting tools.

Best for: Small to mid size businesses with low volume. Flexprice vs Lago goes deeper on credits, entitlements, and enterprise contracts.

Pricing: free to self-host; the Premium cloud plan is custom.

G2 rating: not yet rated on G2.

6. Chargebee

Chargebee is a subscription-first billing platform that added usage-based pricing on top of strong recurring-revenue tooling. 

Usage enters through APIs and integrations, gets rated with tiers, credits, and included allowances, and shows up on one invoice alongside subscriptions. It suits teams running both self-serve plans and negotiated enterprise contracts.

The trade-offs are real. Real-time usage tracking is limited and best suited to end-of-cycle billing, customization can be rigid, and its pricing is a percentage of your billing, which grows as you do. 

Paying a billing vendor more simply because you sold more has never sat right with me, so I'll flag it plainly: Flexprice charges flat plan pricing with no revenue share.

Core features:

• Subscription and usage charges on a single invoice.

• Usage rating with tiers, credits, and included allowances.

• CPQ and quote-to-cash for sales-led deals.

• Multi-currency billing across 100+ currencies.

• Dunning and revenue recognition (ASC 606 and IFRS 15).

Best for: SaaS teams already on Chargebee subscriptions that want to add usage without migrating. Flexprice vs Chargebee covers the subscription-first versus usage-first split.

Pricing: free up to $250K of cumulative billing, then 0.75%; the Performance plan is $7,188/year, and Enterprise is custom.

G2 rating: 4.4/5.

7. Zuora

Zuora is enterprise order-to-revenue software for large teams reconciling subscriptions, one-time charges, and usage under strict financial controls. It handles high transaction volume, account hierarchies, and frequent contract changes, with rating and mediation built into the same system as quoting and invoicing.

It's a heavy platform, and that cuts both ways. Setup is long, and its usage-record ceiling (around 200K) strains the event volumes AI products generate. 

I've never heard anyone describe a Zuora rollout as fast, and for an early API team that time cost is usually the dealbreaker. Teams usually adopt Zuora when billing connects to many internal systems and needs audit-ready reporting.

Core features:

• Usage rating and mediation alongside recurring billing.

• Account hierarchies, amendments, and renewals.

• Order-to-revenue automation with audit-ready reporting.

• Payments, tax, and e-invoicing.

• CPQ and CRM integrations.

Best for: large enterprises with complex, multi-entity billing and compliance requirements.

Pricing: custom, typically annual contracts in the high five figures and up, per third-party reviews.

G2 rating: 3.9/5.

8. Maxio

Maxio (formerly SaaSOptics and Chargify, which merged and rebranded in 2022) is a finance-first platform strong in revenue recognition and SaaS metrics. 

You define per-unit, tiered, volume, prepaid, or hybrid plans, feed usage through APIs or batch uploads, and Maxio turns it into invoices and recognized revenue. Revenue recognition here means matching revenue to when it's earned, which ASC 606, the US accounting standard, requires.

Finance teams tend to drive Maxio adoption, while enforcement stays in the product. Users report a complex setup and unintuitive navigation.

Core features:

• Usage ingestion through APIs or batch uploads.

• Per-unit, tiered, volume, prepaid, and hybrid plans.

• Automated invoicing from usage data.

• Subscription management with proration.

• GAAP and IFRS revenue reporting.

Best for: B2B SaaS teams that need subscription-plus-usage billing with strong financial reporting.

Pricing: custom.

G2 rating: 4.3/5.

9. Moesif

Moesif (acquired by WS02) is primarily API analytics with billing integrations, not a standalone biller. It captures requests, responses, and payloads, defines billing metrics from that data, and then routes to Stripe or Zuora for invoicing. Its strength is deep usage analytics and customer-facing dashboards.

I'd flag this clearly, because it's easy to miscategorize. Moesif is excellent at understanding API usage, but it still needs a billing engine underneath it to actually invoice. If your gap is analytics, it fits. If your gap is billing, you'll pair it with something else.

Core features:

• Real-time API usage tracking of requests, responses, and payloads.

• Custom billing metrics from any request attribute.

• Quota enforcement, alerts, and overage triggers.

• Customer-facing usage dashboards.

• Integrations that route usage to Stripe or Zuora for invoicing.

Best for: API teams that want usage analytics and quota visibility alongside a separate billing system.

Pricing: free tier available; paid plans are custom.

G2 rating: not publicly scored on G2.

10. BillingPlatform

BillingPlatform is a billing mediation software for high-volume, regulated industries like telecom and cloud services. Its mediation engine converts raw API events into billable records, and it supports tiered, volume, and pay-as-you-go models with multi-currency and tax handling.

It's genuinely configurable, which is also why users describe implementation as slow and complex, and better suited to large teams than lean ones.

Core features:

• A mediation engine that turns raw events into billable records.

• Tiered, volume, and pay-as-you-go pricing.

• Multi-dimensional metering across several attributes at once.

• Multi-currency, tax, and localized invoicing.

• REST and SOAP APIs with ERP and CRM integrations.

Best for: Enterprises but if your priority is to roll out faster then maybe not the best choice to go with

Pricing: custom.

G2 rating: 4.7/5.

Why API-first companies need a specialized billing platform

API-first companies need specialized billing because flat subscriptions misprice variable consumption. A customer sending 10,000 API calls costs you very differently from one sending 10 million, yet a fixed fee charges them the same. 

That gap is either lost revenue or an angry customer.

A specialized platform earns its place by doing a few things a general tool won't:

• Meters usage in real time, so every call, payload, or compute cycle gets logged and rated as it happens.

• Supports hybrid models, with a base subscription under usage, credits, overages, or minimums.

• Handles multi-dimensional pricing, charging on requests plus data size plus compute at once.

• Shows customers their own usage, through self-serve dashboards and itemized invoices.

• Scales globally, with tax compliance, multi-currency, and payment-gateway support.

So why not just build it yourself? Here's the honest version. The pricing page is the easy part. 

The hard part is the pipeline underneath it, and it has three steps:

• Ingest every usage event, even when networks and SDKs retry and fire duplicates.

• Aggregate and rate that usage against your pricing rules.

• Invoice it, reconcile it, and do it again next cycle.

Teams quietly lose 4 to 9% of revenue in that pipeline, to double-counting, dropped events, and reconciliation drift. Idempotency is the fix for step one. It means that if the same event arrives twice, the system counts it once. 

When Nikhil, our CTO, ran event pipelines at Zomato's scale, this wasn't a nice-to-have, because without it every retry becomes a double charge on a customer's invoice. That's the class of problem a purpose-built platform exists to solve, and it's why the tools above exist at all.

How to choose usage-based pricing software for your API

Choose your usage-based pricing software by matching the platform to your primary use case, not by feature-count. Here's how the picks break down.

1. API-first and developer-led: you want clean APIs, real-time metering, and control over billing logic. Flexprice and Orb both fit; Flexprice adds credits, entitlements, and cost tracking in one system and stays open source. 

2. AI-native, token and credit heavy: you're billing per token or per model and need credit wallets and per-model cost visibility.  This is Flexprice's core, with Metronome as the dedicated rating layer if you're comfortable in the Stripe ecosystem. For the mechanics, see how to meter LLM token usage for billing.

3. Enterprise and contract-heavy: you need account hierarchies, audit trails, and negotiated terms. Flexprice covers it too with contract versioning and ramped contracts, without the multi-month setup. And if you prefer the implementation and roll out cycle to be months you can think of Zuora or Chargebee as well. 

4. Open-source or self-host: you can't send billing data to a black box. Flexprice and Lago are the two real options, and Flexprice ships every feature in the OSS tier.

5. Simplest possible start: you have light usage on top of subscriptions and want to move today. Stripe Billing is the fastest path, with room to graduate later.

The one criterion that decides most of these is metering complexity. If you only ever count simple API calls, almost anything works. The moment you need to charge on multiple dimensions at once, or blend credits with usage and a subscription on one invoice, the field narrows fast.

What enterprise API teams should check before buying

Enterprise API teams should confirm compliance, deployment, and contract capabilities before committing, because these are the requirements that surface six months after launch, not during the demo. 

The GSC data behind this article is full of queries like "which usage-based billing platforms handle entitlements and enterprise contracts," so this matters to real buyers.

Run through this checklist:

• Compliance: SOC 2 Type II at minimum. Flexprice is SOC 2 Type II compliant.

• Data residency: on-premise or VPC deployment if your data can't leave your walls. Flexprice offers real on-prem, which most usage-based tools don't.

• Contract versioning: a tracked history of every pricing and contract change, so you can prove what a customer agreed to and when.

• Ramped contracts: commitments that step up on a schedule as a pilot scales, without re-implementing billing at each phase.

• Account structure: parent-child accounts and RBAC, so a parent org and its subsidiaries bill correctly and the right people have the right access.

• Reliability: a 99.99%+ uptime SLA, because billing outages are revenue outages.

• Commercial flexibility: custom minimums with overages billed separately, and the ability to grandfather legacy customers on old plans indefinitely.

The uncomfortable truth is that most usage-based tools bolt these on as premium tiers or leave them to your engineers. Flexprice ships them, and ships most of them in the open-source tier, on the enterprise billing software side.

Choosing the right billing partner for your API

Usage-based pricing is now the norm for API-first businesses, and the platform you pick shapes how well your revenue tracks your growth. Map your primary use case first, API-first, AI-native, enterprise, or open-source, then shortlist against that, not against a feature checklist.

If you're building an AI-native or credit-heavy API product, Flexprice is the open-source, developer-first platform designed for multi-dimensional usage, credits, and per-model cost tracking, and it's the one to evaluate first. 

Try it for free, read the docs, or book a demo if you want to walk through an enterprise setup with our team.