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October 2026: What Changed for ActivityPub Developers

· 3 min read
SocialDocs Team
SocialDocs Team
Documentation Team

A dated roundup of the changes since June 2026 that affect people building ActivityPub software, and what we updated on SocialDocs as a result.

Mastodon 4.6 and 4.7​

  • Mastodon 4.6 (17 June 2026) added collections based on FEP-7aa9, email subscriptions to posts, profile improvements and new profile-editing API endpoints.
  • Mastodon 4.7 (20 August 2026) mostly reworks internals. Per the release notes, it:
    • uses the ActivityPub actor id as the primary identifier instead of the WebFinger handle, so remote accounts that change handles are renamed rather than duplicated;
    • sends RFC 9421 HTTP Message Signatures as a fallback to the earlier draft, and supports Ed25519 signatures;
    • verifies FEP-8b32 Object Integrity Proofs;
    • adds inbound support for FEP-521a and Link objects in attachment (FEP-8967).
  • Mastodon's releases page has the current patch version (4.7.3 as of 1 October 2026).

FEP-7628 (Move actor) is FINAL​

FEP-7628 was finalized on 26 August 2026, giving account migration a stable specification.

W3C Social Web Working Group​

The Working Group chartered in January 2026 aimed to publish backwards-compatible updates to ActivityPub, Activity Streams 2.0 and Activity Vocabulary in Q3 2026. That target slipped: no new version has been published to /TR yet. Work continues in the ActivityPub Editor's Draft, and at the 2 October joint meeting members discussed trying to publish a draft around TPAC 2026 (Dublin, 26–30 October). See W3C groups.

Lemmy 1.0 is still in beta​

The latest stable Lemmy is 0.19.20 (21 July 2026); 1.0.0-beta.2 came out on 11 September 2026 (releases). Lemmy 1.0 introduces API v4, with a v3 compatibility layer for existing clients.

fediverse.observer has shut down​

The fediverse.observer statistics site is gone; its domain now redirects to a domain-parking page (SocialHub thread). We removed our links to it. FediDB remains available for network statistics.

What we changed on SocialDocs​

  • Added security warnings to pages whose inbox and signature-verification code is unsafe to copy, tracked in issue #37.
  • Removed references to libraries, packages and tools that do not exist.
  • Corrected factual errors, including the ActivityPub editors, as:Public delivery and Mastodon's signature time window.
  • Added site search and "last updated" dates on docs pages.
  • Published The Complete Guide to ActivityPub Development in 2026.

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