HubSpot sets September 2027 end of support for v1 to v3 APIs and legacy apps

HubSpot used its Fall Spotlight on September 15, 2026 to announce that v1 to v3 APIs, legacy public apps and legacy private apps will become unsupported, opening a 12-month migration window. The changelog post covers breaking changes only. HubSpot says its developer home now shows a tasks card listing apps that call APIs becoming unsupported, based on runtime calls rather than source code. It recommends Service Keys for new lightweight and AI agent integrations in place of legacy private apps.

The details

• Enforcement date for v1 to v3 APIs, legacy public apps and legacy private apps: September 2027.
• Legacy public apps are those created before June 23, 2026 on the pre-Projects architecture.
• Legacy private app creation ended September 28, 2026 (new accounts) and October 26, 2026 (existing accounts).
• Apps on Projects 2025.2 or older must move to 2026.09 by March 2027.
• Marketplace apps on unsupported APIs lose certification; apps on legacy architecture are eligible for delisting.
• HubSpot says full per-endpoint replacement documentation will arrive with the March 2027 release.

Context

HubSpot introduced date-based API versioning in March 2026 and confirmed in May 2026 that v4 APIs become unsupported in March 2027. This announcement completes the timeline for older versions. GTM Tech News covered the customer-facing Fall 2026 Spotlight on September 16, 2026; this developer notice was published alongside it and sets the deadlines integrations must meet.

Not disclosed

• Whether unsupported endpoints will be shut off or only left unmaintained
• Which legacy endpoints lack replacement paths today
• Support available to customers with in-house integrations