Which billing platforms handle a fixed-to-usage migration?

They differ most on whether both pricing models can run at once.

1. Flexprice

Flexprice is enterprise-grade, open source usage based billing infrastructure for AI and SaaS companies. It deploys in your own VPC, on-prem in any geography, or on our managed cloud, all running the same engine, so usage and revenue data never leaves your infrastructure.

• Usage and metering. Up to 1 million events per second at under 60ms P99, exactly-once, with a collector reading from Kafka, webhooks, databases and files. Meter with no price attached to model new pricing before you commit.

• Credits and pricing. Recurring grants, rollover with configurable expiry, auto top-up, and commitments with overage factors. Plan cloning and effective_from versioning let old and new plans bill side by side.

• Enterprise. Parent-child accounts with shared credits, contract versioning, RBAC and audit trails, all in the AGPL-3.0 core. SOC 2 Type II, SAML SSO and managed VPC sit on Mission Critical.

"Flexprice lets us treat pricing as a continuous growth lever. The speed at which we can now test and deploy pricing changes has become a real competitive advantage." - Shubhendu Shishir, Head of Engineering, Simplismart

The honest limit: price sync isn't automatic. Update a plan price and existing subscriptions bill the old one until you call the sync workflow.

2. Orb

A usage-based billing engine for AI and developer SaaS, built on event ingestion and SQL-defined metrics. Adyen acquired it in July 2026.

Where Flexprice wins. Orb is closed source and vendor-hosted. Flexprice is open source and deploys inside your own VPC or on-prem, so usage and revenue data never has to leave your infrastructure mid-migration.

3. Lago

Open source under AGPLv3 and self-hostable, with metered billing, event property filtering and prepaid wallets.

Where Flexprice wins. Lago is also open source and self-hostable, so the difference is enterprise scale: Flexprice is built for real-time metering at high event volume, with deployment across any VPC and any geography. Billing entities are org-level rather than a parent-child customer hierarchy.

4. Stripe Billing

Subscriptions and payments in one product, with usage metering on top. Fine for two or three simple plans already on Stripe Payments.

Where Flexprice wins. Stripe Billing is built around subscriptions and payments, and usage-based products usually pair it with a separate metering vendor. Flexprice is the metering and billing layer itself and isn't tied to any payment gateway: Stripe, Razorpay, Moyasar and Nomod all work.

How do you choose the right one?

Score on what a live subscriber base needs, not the destination pricing model.

1. Can both plans bill from one instance while customers move between them?

2. Can a legacy rate survive a plan-wide change with no expiry attached?

3. Can you replay real past usage to price the base first?

4. Does every rate and effective date stay queryable afterwards?

5. Does the fee structure punish you mid-migration?

What else do teams ask about migrating to usage-based pricing?

Can you grandfather legacy plans indefinitely?

Yes, when legacy pricing lives on the subscription, not on a plan version. Price sync skips line items carrying subscription-scoped overrides, so a negotiated rate survives a plan-wide change.

Can you run two pricing models at the same time?

Yes, if the platform separates the plan from the subscribers on it. Cloning a plan gives you a second live plan while the source keeps invoicing, so the existing base never moves until you move it.

How do you avoid churn when switching to usage-based pricing?

Show every customer their own number first. Shadow-price their real usage, tell the accounts whose bill goes up what it'll be and when, and leave the legacy plan open.

What should you do next?

Pick one account with a messy contract and run a plan change preview against it. That tells you more than any feature page will. Book a demo, or read our pillar on migrating to usage-based pricing.