generated: '2026-08-13'
method: searched
source: >-
  https://api-docs.omnisend.com/reference/overview,
  https://api-docs.omnisend.com/docs/migrate-from-v5-to-v2026-03-15,
  https://api-docs.omnisend.com/docs/migrate-from-v3-to-v2026-03-15,
  https://api-docs.omnisend.com/docs/migrate-from-v3-with-an-ai-agent,
  https://status.omnisend.com, https://www.omnisend.com/changelog/,
  and the harvested openapi/omnisend-*-openapi.yml contracts
description: >-
  Omnisend re-cut its API lifecycle at version 2026-03-15: version moved out of the URL path and into
  a required `Omnisend-Version` request header, the base path became https://api.omnisend.com/api,
  and every operation now declares a 410 "API version has been retired" response. Three earlier
  URL-path versions (v3, v4.0, v5) remain published as branches on the documentation host.

versioning:
  scheme: date-based, header-negotiated
  header: Omnisend-Version
  current: '2026-03-15'
  current_base: https://api.omnisend.com/api
  required: true
  default_in_spec: '2026-03-15'
  resolution: >-
    A date between releases resolves to the nearest earlier supported version (documented on the
    event-metadata query operation).
  history:
    - version: v3
      base: https://api.omnisend.com/v3
      status: legacy
      migration: https://api-docs.omnisend.com/docs/migrate-from-v3-to-v2026-03-15
    - version: '4.0'
      base: https://api.omnisend.com/v4
      status: legacy
      note: Published as a documentation branch; no migration guide.
    - version: v5
      base: https://api.omnisend.com/v5
      status: legacy
      migration: https://api-docs.omnisend.com/docs/migrate-from-v5-to-v2026-03-15
      note: >-
        Still live — https://api.omnisend.com/v5 answers 400 "API key or access token not provided"
        rather than 404 or 410. Omnisend's own MCP server v2 still routes GET automations through
        /v5/automations while the published contract serves it at /api/automations.
    - version: '2026-preview'
      status: preview
      note: A documentation branch carrying preview definitions (campaigns, automations, event metadata, forms) ahead of a dated release.
    - version: '2026-03-15'
      status: current

deprecation:
  policy_published: true
  policy_url: https://api-docs.omnisend.com/docs/migrate-from-v5-to-v2026-03-15
  mechanism: >-
    Version retirement is signalled in-band as HTTP 410 Gone with an RFC 9457 body titled
    "API version has been retired". The response is declared on 73 of 82 operations in the harvested
    contracts, so it is a contract guarantee, not a footnote.
  headers:
    sunset: false
    deprecation: false
    note: >-
      Omnisend does NOT emit RFC 8594 `Sunset` or the `Deprecation` header. There is no advance
      machine-readable warning — a client learns a version is gone only when it starts failing with
      410. Migration guides carry no published retirement date for v3/v4/v5.
  migration_guides:
    - https://api-docs.omnisend.com/docs/migrate-from-v5-to-v2026-03-15
    - https://api-docs.omnisend.com/docs/migrate-from-v3-to-v2026-03-15
    - https://api-docs.omnisend.com/docs/migrate-from-v3-with-an-ai-agent
  note: >-
    The third guide is notable — Omnisend publishes an agent-driven migration path, telling
    integrators to hand the migration to an AI agent.

deprecated_operations:
  count: 0
  note: >-
    No operation in any of the 15 harvested specs carries `deprecated: true`. Deprecation is
    expressed at the version level, not per operation.

status_page:
  url: https://status.omnisend.com
  status: 200
  probed: '2026-08-13'
  note: Live status page linked from the site footer.

changelog:
  url: https://www.omnisend.com/changelog/
  detail: changelog/omnisend-changelog.yml
  note: >-
    apis.yml previously pointed at https://api-docs.omnisend.com/changelog, which returns 404. The
    real dated changelog is on the marketing host.

roadmap:
  url: https://www.omnisend.com/changelog/#roadmap
  note: A Roadmap tab on the same page as the changelog; its content is loaded client-side.

sla:
  published: false
  note: >-
    No public SLA or uptime commitment. Omnisend's pricing page describes an Enterprise tier with a
    "Custom SLA" negotiated per contract; nothing is published for self-serve plans.

support:
  channels:
    - https://support.omnisend.com
    - https://www.omnisend.com/contact-us/support
    - mailto:integrations@omnisend.com
  api_error_log: https://app.omnisend.com/integrations/api-access-logs