1.21.9 Pre-Release 1 — release journal

What 1.21.9-pre1 changed for data packs, measured against 25w37a, the build before it. Released 2025-09-16; development build — not a release.

⚠ Entries removed

16 registry entries were removed. A pack that names one of them will fail to parse where it does.

Formats

	25w37a	1.21.9-pre1
Data pack format	87.0	87.1 moved
Resource pack format	69.0	69.0
Data version	4547	4549

Registries

16 entries added and 16 removed across 1 registry.

Registry	Change	Added	Removed
`outgoing_rpc_methods`	changed	`notification/allowlist/added`, `notification/allowlist/removed`, `notification/bans/added`, `notification/bans/removed`, `notification/gamerules/updated`, `notification/ip_bans/added`, `notification/ip_bans/removed`, `notification/operators/added`, `notification/operators/removed`, `notification/players/joined`, `notification/players/left`, `notification/server/saved`, `notification/server/saving`, `notification/server/started`, `notification/server/status`, `notification/server/stopping`	`notification:allowlist/added`, `notification:allowlist/removed`, `notification:bans/added`, `notification:bans/removed`, `notification:gamerules/updated`, `notification:ip_bans/added`, `notification:ip_bans/removed`, `notification:operators/added`, `notification:operators/removed`, `notification:players/joined`, `notification:players/left`, `notification:server/saved`, `notification:server/saving`, `notification:server/started`, `notification:server/status`, `notification:server/stopping`

The official notes

Read the 1.21.9 Pre-Release 1 article on minecraft.net.

That article's technical changes are grouped under these headings — open it for the detail:

Data Pack Version 87.1
Mannequins
Commands
Data Components
Entity Data
Loot Functions

Minecraft Wiki page for 1.21.9-pre1.

In the journal

← 25w37a · All builds · 1.21.9-pre2 →

Sources

misode/mcmeta — 1.21.9-pre1 summary — formats and registries, generated from the game’s own data.
minecraft.net — 1.21.9 Pre-Release 1 — section names only.