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HubSpot Legacy Private App Migration: Dates and Steps

HubSpot has announced two changes for legacy private apps: new ones can no longer be created, and existing ones must move to Projects-based private apps. Here is what HubSpot's developer changelog says, with dates, and a plain order of work for a migration. Sources: Legacy Private App Creation Being Disabled and Legacy APIs and Apps: What's Going Unsupported and When, both retrieved 2026-10-13. Check them for updates before you plan.

The dates

• September 28, 2026: legacy private app creation is disabled for HubSpot accounts created on or after that date.
• October 26, 2026: legacy private app creation is disabled for accounts created before September 28, 2026.
• March 30, 2027: support for v4 APIs ends.
• September 2027: enforcement date. v1-v3 APIs become unsupported, and legacy private apps must have migrated to Projects-based private apps.

What October 26 does not do

HubSpot says all existing legacy private apps continue to work as-is. The change removes the ability to create new ones. So October 26 does not break a working integration. It removes the old route for a new one.

What to use for new integrations

HubSpot recommends Service Keys for new in-account API integrations, created at Settings > Integrations > Service Keys.

A migration order we use

1. List every legacy private app. Name, owner, scopes, and what it is used for.
2. Check which APIs each one calls. HubSpot says the developer home tasks card shows apps that use APIs becoming unsupported, and that detection checks API calls at runtime, not your source code.
3. Plan the API version move. HubSpot says to migrate directly to date-based versioning and not to use v3 or v4 as an intermediate step.
4. Pick a path per app. A Service Key for a lightweight integration, or a Projects-based private app.
5. Test, then rotate. Move one app at a time, test it, and retire the old token only when the new one works.

If you want a written audit

Our HubSpot legacy private app readiness audit turns your screenshots into an app inventory, a written audit of which apps are at risk and by when, and a migration checklist in priority order. We never need your token values. We are independent and not affiliated with HubSpot. Fully asynchronous - no meeting required.