minecraft_protocol/versions/1.21.md

Java Edition 1.21.x — "Tricky Trials" and the Long Patch Series

Protocol numbers: 767 (1.21/1.21.1) · 768 (1.21.2/1.21.3) · 769 (1.21.4) · 770 (1.21.5) · 771 (1.21.6) · 772 (1.21.7/1.21.8) · 773 (1.21.9/1.21.10) · 774 (1.21.11)

Release span: June 13, 2024 (1.21) — December 9, 2025 (1.21.11) — 8 distinct protocol versions across 11 game releases.

Sources:

• MCWIKI: https://minecraft.wiki/w/Java_Edition_1.21[.X] (fetched 2026-06-19)
• VV: /tmp/mcproto-refs/ViaVersion/common/src/main/java/com/viaversion/viaversion/protocols/v1_20_5to1_21/ … v1_21_9to1_21_11/ (Protocol*.java + packet enums)
• VV-LOG: git -C /tmp/mcproto-refs/ViaVersion log --oneline -- common/.../protocols/<pkg> (fetched 2026-06-19)
• MD: /tmp/mcproto-refs/minecraft-data/data/pc/1.21[.x]/version.json

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Headline

1.21 "Tricky Trials" (June 2024) was the major combat/adventure update: trial chambers, breeze mob, mace weapon, wind charge, crafter block, copper and tuff block variants, four new status effects. Patch releases after it were unusually numerous — 10 patches over 18 months spanning the "Wild West" (1.21.2: bundles), "Winter Drop" (1.21.4: pale garden/creaking), animal variants (1.21.5), "Chase the Skies" (1.21.6: happy ghasts, dialog system), "Copper Age" (1.21.9: copper golem/equipment), and "Mounts of Mayhem" (1.21.11: spears, nautilus, dimension attribute overhaul). Each sub-update bumped the protocol, producing 8 distinct wire versions inside a single major release line.

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Protocol bump summary

Protocol	MC versions	Released	Key protocol change
767	1.21, 1.21.1	2024-06-13, 2024-08-08	First 1.21 wire (attribute UUID→ID remap, PROJECTILE_POWER scalar)
768	1.21.2, 1.21.3	2024-10-22, 2024-10-23	Major: ENTITY_POSITION_SYNC + MOVE_MINECART_ALONG_TRACK new; serverbound CLIENT_TICK_END + BUNDLE_ITEM_SELECTED; full item component rebuild; new entity types (Salmon sizes, etc.)
769	1.21.4	2024-12-03	PICK_ITEM split into PICK_ITEM_FROM_BLOCK/PICK_ITEM_FROM_ENTITY; LEVEL_PARTICLES gets always_show field; CUSTOM_MODEL_DATA format extended (1_21_4); PROFILE_ACTIONS_ENUM gains "show hat" bit
770	1.21.5	2025-03-25	ADD_EXPERIENCE_ORB removed (merged into ADD_ENTITY); PLAYER_ROTATION packet added; PLAYER_CHAT gets message-index prefix; serverbounds: SET_TEST_BLOCK + TEST_INSTANCE_BLOCK_ACTION (test framework); PLAYER_LOADED new; large item component churn (UNBREAKABLE, ENCHANTMENTS, ATTRIBUTE_MODIFIERS, EQUIPPABLE, INSTRUMENT, JUKEBOX_PLAYABLE, TRIM, many variants bump to 1_21_5)
771	1.21.6	2025-06-17	Dialog system: CLEAR_DIALOG + SHOW_DIALOG new (play + config); CUSTOM_CLICK_ACTION new serverbound (play + config); TRACKED_WAYPOINT new; CHANGE_DIFFICULTY changes type (unsigned byte → varint); CHANGE_GAME_MODE new serverbound; sneak/shift actions removed from PLAYER_COMMAND (now absorbed into PLAYER_INPUT); ATTRIBUTE_MODIFIERS → 1_21_6, EQUIPPABLE → 1_21_6
772	1.21.7, 1.21.8	2025-06-30, 2025-07-17	Incremental: entity/item data remapping only (block/item ID changes); no new packet types; 1.21.8 was graphics bug-fix only
773	1.21.9, 1.21.10	2025-09-30, 2025-10-07	ADD_ENTITY velocity field type changed (short×3 → LOW_PRECISION_VECTOR); SET_ENTITY_MOTION same; PLAYER_ROTATION gets "relative" boolean fields; four new DEBUG_* packets (DEBUG_BLOCK_VALUE, DEBUG_CHUNK_VALUE, DEBUG_ENTITY_VALUE, DEBUG_EVENT); GAME_EVENT_TEST_HIGHLIGHT_POS new; EXPLODE restructured (radius+count fields moved to PROJECTILE_POWER); config: CODE_OF_CONDUCT added; copper golem entity + copper equipment block/item IDs
774	1.21.11	2025-12-09	HORSE_SCREEN_OPEN → MOUNT_SCREEN_OPEN rename; new entity types (zombie_nautilus, new mounts); zombie_nautilus_variant + timeline registries injected at FINISH_CONFIGURATION; massive dimension_type field migration (many fields → attributes NBT compound); worldgen/biome similarly gains attributes; new item components: ATTACK_RANGE, USE_EFFECTS, MINIMUM_ATTACK_CHARGE, DAMAGE_TYPE, PIERCING_WEAPON, KINETIC_WEAPON, SWING_ANIMATION, ZOMBIE_NAUTILUS_VARIANT

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767 — 1.21 / 1.21.1 (June 13 / August 8, 2024)

Gameplay headline

Tricky Trials: trial chambers, breeze mob, mace+heavy core, wind charge, crafter block, copper/tuff variant blocks, four status effects (Wind Charged, Weaving, Oozing, Infested). First release requiring 64-bit OS and Java 21+. MCWIKI 1.21

1.21.1 hotfixed two security exploits (update suppression block-entity swap; server crash via malicious command-completion target selector causing stack exhaustion) plus two gameplay bugs. Same protocol 767. Servers running 1.21.1 are compatible with 1.21 clients. MCWIKI 1.21.1

Protocol changes (766→767)

VV package: v1_20_5to1_21/ (Protocol1_20_5To1_21.java)

Play state — clientbound (0x00–0x7B): Packet set identical in count/IDs to 1.20.5 (ClientboundPackets1_21 enum ends at SERVER_LINKS 0x7B = 124 entries). Notable: PROJECTILE_POWER (0x79) already existed as of 1.20.5 but its payload changed — 1.21 converts the separate x/y/z doubles (three fields) into a single acceleration_power scalar (magnitude of the velocity vector). VV does this inline: Protocol1_20_5To1_21.java:registerPackets() reads the three doubles, computes sqrt(x²+y²+z²), writes one double. [VV Protocol1_20_5To1_21.java:registerPackets()]

Attribute modifiers: UUID-keyed modifiers in UPDATE_ATTRIBUTES replaced by string IDs. VV maps UUID→string via AttributeModifierMappings1_21. Bidirectional mapping: server sends string IDs, old clients need UUIDs, VV translates. [VV Protocol1_20_5To1_21.java:registerPackets(), AttributeModifierMappings1_21]

Chat type holder: DISGUISED_CHAT and PLAYER_CHAT chat-type field changed from plain varint to Holder<ChatType> (inline or registry reference). VV wraps the varint into ChatType.TYPE holder. [VV Protocol1_20_5To1_21.java:registerPackets()]

Item components: The 1.20.5 component set carries forward. VV's VersionedTypes.V1_21.structuredData filler enumerates which components exist at this version — all keys use 1_20_5-suffixed variants except FOOD1_21, JUKEBOX_PLAYABLE1_21, ATTRIBUTE_MODIFIERS1_21. [VV Protocol1_20_5To1_21.java:onMappingDataLoaded()]

New entity tags: blocks_wind_charge_explosions (block), several entity tags (can_turn_in_boats, deflects_projectiles, immune_to_infested, immune_to_oozing, no_anger_from_wind_charge). Enchantment tags added (curse, double_trade_price, in_enchanting_table, etc.). [VV Protocol1_20_5To1_21.java:onMappingDataLoaded()]

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768 — 1.21.2 / 1.21.3 (October 22 / October 23, 2024)

Gameplay headline

Bundles (dyeable, store up to 64 mixed items), new banner patterns (field masoned, bordure indented). Experimental content: Minecart Improvements, Redstone Experiments, Winter Drop (pale garden biome, creaking mob) gated behind feature flags. Significant ender pearl chunk-loading change. MCWIKI 1.21.2

1.21.3 hotfixed salmon size regression (small salmon incorrectly downsized on world load) and Realms resource-pack failure. Same protocol 768. MCWIKI 1.21.3

MD confirms: data/pc/1.21.3/version.json = 768.

Protocol changes (767→768)

VV package: v1_21to1_21_2/ (Protocol1_21To1_21_2.java)

This is the most substantial bump in the 1.21 line.

New clientbound play packets

• ENTITY_POSITION_SYNC (0x20): New packet for authoritative entity position sync (replaces the indirect position-via-teleport path for most entities). All subsequent packet IDs shift up by 1. [VV ClientboundPackets1_21_2.java:0x20]
• MOVE_MINECART_ALONG_TRACK (0x31): New dedicated minecart movement packet for the experimental Minecart Improvements feature. [VV ClientboundPackets1_21_2.java:0x31]
• SET_CURSOR_ITEM (0x5A): Sends the item on the cursor (held item in inventory GUI). Was previously implicit. [VV ClientboundPackets1_21_2.java:0x5A]
• SET_HELD_SLOT (0x63): Replaces SET_CARRIED_ITEM rename. [VV ClientboundPackets1_21_2.java:0x63]
• SET_PLAYER_INVENTORY (0x66): Sends a specific slot of the player inventory. [VV ClientboundPackets1_21_2.java:0x66]

Total play clientbound count grows from 124 (0x7B) to 131 (0x82).

New serverbound play packets

• BUNDLE_ITEM_SELECTED (0x02): Client reports which item inside a bundle was selected. VV cancels this (no equivalent in 1.21). [VV Protocol1_21To1_21_2.java:cancelServerbound()]
• CLIENT_TICK_END (0x0B): Client sends at end of each tick. VV cancels. [VV Protocol1_21To1_21_2.java:cancelServerbound()]

Packet field changes

• LOGIN_FINISHED (login state): strict_error_handling boolean field removed. VV reads and discards it. [VV Protocol1_21To1_21_2.java:registerPackets()]
• SET_TIME: doDaylightCycle was encoded as negative day-time; now explicit doDaylightCycle: boolean field added. VV converts the sign-encoding to explicit field. [VV Protocol1_21To1_21_2.java:registerPackets()]
• PLAYER_INFO_UPDATE: PROFILE_ACTIONS_ENUM updated to 1_21_2 variant. Display-name entries now include component rewriting. [VV Protocol1_21To1_21_2.java:replaceClientbound()]
• UPDATE_ATTRIBUTES: Attribute modifier format: UUID field removed, modifiers now have string ID only (already done in 767 serverside, now serverbound clean-up). VV tracks generic.max_health to compute max health for 1.21 clients. [VV Protocol1_21To1_21_2.java:appendClientbound()]

Item component changes (notable)

• DAMAGE_RESISTANT → DAMAGE_RESISTANT1_21_2 (format change)
• FOOD → FOOD1_21_2 (split into food + consumable components)
• CONSUMABLE1_21_2, USE_COOLDOWN, EQUIPPABLE1_21_2, ITEM_MODEL, GLIDER, TOOLTIP_STYLE, DEATH_PROTECTION added
• REPAIRABLE, ENCHANTABLE added
• LOCK → LOCK1_21_2, POTION_CONTENTS → POTION_CONTENTS1_21_2, INSTRUMENT → INSTRUMENT1_21_2, TRIM → TRIM1_21_2

[VV Protocol1_21To1_21_2.java:onMappingDataLoaded()]

Damage types added

ender_pearl and mace_smash damage types added to registry. [VV Protocol1_21To1_21_2.java:registryDataRewriter()]

Chunk-load workaround

1.21.2 introduced a rendering bug: if a loaded chunk received new data without being unloaded first, it wouldn't render correctly. VV injects a ChunkLoadTracker that forces chunk unload before re-send, only for 1.21.2 clients (not 1.21.3 which got the 1.21.2 packet set, as 1.21.4 fixed the bug). [VV Protocol1_21To1_21_2.java:init()]

CLIENT_INFORMATION

New particle_status varint field added at end. VV reads and discards it when translating to 1.21. [VV Protocol1_21To1_21_2.java:clientInformation()]

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769 — 1.21.4 (December 3, 2024)

Gameplay headline

Pale garden biome + pale oak wood set; creaking heart block; creaking mob (freezes when observed); eyeblossom; resin blocks. Spawn damage immunity removed. Water Breathing/Conduit Power now restore oxygen. MCWIKI 1.21.4

Protocol changes (768→769)

VV package: v1_21_2to1_21_4/ (Protocol1_21_2To1_21_4.java)

Relatively lightweight protocol bump — no new packet types, primarily field changes and item-component format updates.

• PICK_ITEM split: Serverbound PICK_ITEM (0x22) split into PICK_ITEM_FROM_BLOCK (0x22) and PICK_ITEM_FROM_ENTITY (0x23). VV provides a PickItemProvider to handle the split. [VV Protocol1_21_2To1_21_4.java:register()]
• LEVEL_PARTICLES: always_show boolean field added after override_limiter. VV writes false for it when translating down. [VV Protocol1_21_2To1_21_4.java:registerPackets() replaceClientbound(LEVEL_PARTICLES)]
• PLAYER_INFO_UPDATE: PROFILE_ACTIONS_ENUM → 1_21_4 variant (adds "show hat" action). VV writes true by default. [VV Protocol1_21_2To1_21_4.java:registerPackets()]
• Item components: CUSTOM_MODEL_DATA → 1_21_4 (format extended), TRIM → 1_21_4.
• PLAYER_LOADED serverbound: Added (0x2A in 1.21.5 but arrives at 768→769 boundary).
• VV does NOT add a ChunkLoadTracker for 1.21.4 clients — Mojang fixed the rendering bug in this release. [VV Protocol1_21To1_21_2.java:init() comment]

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770 — 1.21.5 (March 25, 2025)

Gameplay headline

Farm animal variants (cold/warm/temperate pigs, cows, chickens with biome-based spawning), new decorative plants (leaf litter, wildflowers, bushes, firefly bushes), wolf sound variants (7). Game test framework (/test command, test blocks). Text components switch from JSON to SNBT. MCWIKI 1.21.5

Protocol changes (769→770)

VV package: v1_21_4to1_21_5/ (Protocol1_21_4To1_21_5.java)

This is one of the larger protocol bumps: packet added/removed and major item-component churn.

Packet additions and removals

Clientbound play:

• ADD_EXPERIENCE_ORB removed. Experience orbs now spawn via the regular ADD_ENTITY packet (entity type experience_orb). All subsequent IDs shift. [VV ClientboundPackets1_21_5.java — no ADD_EXPERIENCE_ORB entry; 1.21 enum had it at 0x02]
• PLAYER_ROTATION (0x42) added: Server sends player rotation authoritative update. Separate from PLAYER_POSITION. [VV ClientboundPackets1_21_5.java:0x42]
• TEST_INSTANCE_BLOCK_STATUS (0x77): New packet for the game test framework. [VV ClientboundPackets1_21_5.java:0x77]

Serverbound play (vs 1.21.4):

• PICK_ITEM_FROM_BLOCK (0x22), PICK_ITEM_FROM_ENTITY (0x23) — carried from 769
• PLAYER_LOADED (0x2A): New — client signals it has loaded the world. [VV ServerboundPackets1_21_5.java:0x2A]
• SET_TEST_BLOCK (0x39): Test framework. VV cancels. [VV Protocol1_21_4To1_21_5.java:cancelServerbound()]
• TEST_INSTANCE_BLOCK_ACTION (0x3D): Test framework. VV cancels. [VV Protocol1_21_4To1_21_5.java:cancelServerbound()]

Packet field changes

• PLAYER_CHAT: Message-index varint added as first field. VV synthesizes this using MessageIndexStorage (tracks per-connection index). [VV Protocol1_21_4To1_21_5.java:replaceClientbound(PLAYER_CHAT), MessageIndexStorage]
• CHAT_COMMAND_SIGNED and CHAT (serverbound): checksum: byte field added at end. VV reads and drops it. [VV Protocol1_21_4To1_21_5.java:registerServerbound(CHAT_COMMAND_SIGNED), registerServerbound(CHAT)]
• wolf_variant registry: assets field restructured — wild_texture, tame_texture, angry_texture moved under assets compound; biomes field removed. VV remaps on registry send. [VV Protocol1_21_4To1_21_5.java:registryDataRewriter handler for wolf_variant]

Item component changes (major churn)

Many component keys changed to 1_21_5-suffixed variants:

• UNBREAKABLE → 1_21_5, ENCHANTMENTS → 1_21_5, STORED_ENCHANTMENTS → 1_21_5
• DYED_COLOR → 1_21_5, TRIM → 1_21_5, ATTRIBUTE_MODIFIERS → 1_21_5
• EQUIPPABLE → 1_21_5, TOOL → 1_21_5, INSTRUMENT → 1_21_5, JUKEBOX_PLAYABLE → 1_21_5
• New components added: BLOCKS_ATTACKS1_21_5 (shield-like), PROVIDES_BANNER_PATTERNS1_21_5, TOOLTIP_DISPLAY, WEAPON, POTION_DURATION_SCALE, PROVIDES_TRIM_MATERIAL1_21_5, BREAK_SOUND
• Mob-variant components as items: VILLAGER_VARIANT, WOLF_VARIANT, WOLF_COLLAR, FOX_VARIANT, SALMON_SIZE, PARROT_VARIANT, TROPICAL_FISH_*, MOOSHROOM_VARIANT, RABBIT_VARIANT, PIG_VARIANT, FROG_VARIANT, HORSE_VARIANT, PAINTING_VARIANT, LLAMA_VARIANT, AXOLOTL_VARIANT, CAT_VARIANT, CAT_COLLAR, SHEEP_COLOR, SHULKER_COLOR, COW_VARIANT, CHICKEN_VARIANT1_21_5, WOLF_SOUND_VARIANT — all bucket/spawn-egg entity variant data is now carried as item components.

[VV Protocol1_21_4To1_21_5.java:onMappingDataLoaded()]

Smithing trim recipe slot display change

Trim pattern slot display format changed — VV substitutes a placeholder (holder index 0) when translating smithing-trim recipe packets down. [VV Protocol1_21_4To1_21_5.java recipeRewriter anonymous class]

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771 — 1.21.6 (June 17, 2025)

Gameplay headline

"Chase the Skies" — rideable happy ghasts (up to 4 riders, colored harnesses); locator bar (shows other players' direction/distance in HUD); mob-to-mob leads; craftable saddles; waypoints. Dialog system (server-controlled modal UI). MCWIKI 1.21.6

Protocol changes (770→771)

VV package: v1_21_5to1_21_6/ (Protocol1_21_5To1_21_6.java)

New packets

Clientbound play:

• TRACKED_WAYPOINT (0x83): Waypoint tracking for the locator bar feature. [VV ClientboundPackets1_21_6.java:0x83]
• CLEAR_DIALOG (0x84): Dismiss the current server dialog. [VV ClientboundPackets1_21_6.java:0x84]
• SHOW_DIALOG (0x85): Display a dialog to the player. [VV ClientboundPackets1_21_6.java:0x85]

Configuration state — clientbound:

• CLEAR_DIALOG (0x11) and SHOW_DIALOG (0x12) also appear in Configuration state — dialogs can be shown during config phase. [VV ClientboundConfigurationPackets1_21_6.java:0x11,0x12]

Serverbound play:

• CHANGE_GAME_MODE (0x04): New packet for switching game mode. VV translates this to CHAT_COMMAND (/gamemode <name>) for 1.21.5 servers. [VV Protocol1_21_5To1_21_6.java:registerServerbound(CHANGE_GAME_MODE)]
• CUSTOM_CLICK_ACTION (0x41): New serverbound packet sent when a player interacts with a dialog element. VV cancels (no equivalent). [VV Protocol1_21_5To1_21_6.java:cancelServerbound(CUSTOM_CLICK_ACTION)]

Packet field changes

• CHANGE_DIFFICULTY: Difficulty value changes type from unsigned byte to varint. VV converts both directions. [VV Protocol1_21_5To1_21_6.java:registerClientbound(CHANGE_DIFFICULTY), registerServerbound(CHANGE_DIFFICULTY)]
• PLAYER_COMMAND: press_shift_key (action 0) and release_shift_key (action 1) removed — sneak is now a PLAYER_INPUT flag. All remaining actions shift down by 2. VV synthesizes press_shift_key/release_shift_key from PLAYER_INPUT's sneak flag, using SneakStorage to track state changes. [VV EntityPacketRewriter1_21_6.java:registerServerbound(PLAYER_COMMAND), registerServerbound(PLAYER_INPUT)]

Configuration: dialog registry injection

At FINISH_CONFIGURATION, VV synthesizes a minecraft:dialog registry entry (server_links dialog type) and sends it as REGISTRY_DATA — vanilla servers don't send this so older clients wouldn't see server links dialogs. [VV EntityPacketRewriter1_21_6.java:appendClientbound(FINISH_CONFIGURATION)]

Dimension type: cloud_height defaults

VV patches dimension-type registry entries to inject a default cloud_height: 192 for overworld-like dimensions, since 1.21.6 clients render clouds based on this field. [VV Protocol1_21_5To1_21_6.java:registryDataRewriter handler for dimension_type]

Item components

• ATTRIBUTE_MODIFIERS → 1_21_6, EQUIPPABLE → 1_21_6

[VV Protocol1_21_5To1_21_6.java:onMappingDataLoaded()]

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772 — 1.21.7 / 1.21.8 (June 30 / July 17, 2025)

Gameplay headline

1.21.7: New music disc "Lava Chicken" (Hyper Potions, from chicken jockey kill); new painting "Dennis" (3×3, A Minecraft Movie tie-in). 16 bug fixes (AMD/Qualcomm rendering, texture atlas leaks). MCWIKI 1.21.7

1.21.8: Graphics bug-fix only — Intel Gen11 shading errors, inventory item-color glitches on Intel integrated graphics. Same protocol 772. MCWIKI 1.21.8

Protocol changes (771→772)

VV package: v1_21_6to1_21_7/ (Protocol1_21_6To1_21_7.java)

Purely incremental — no new packet types. Same clientbound/serverbound enum as 771. VV's Protocol1_21_6To1_21_7 class has an empty registerPackets() body; translation is limited to block/item/entity ID remapping and dialog-packet item rewriting. [VV Protocol1_21_6To1_21_7.java:registerPackets()]

The git log shows 6b74116ff Handle item changes in dialog packets as the main content commit — items embedded in SHOW_DIALOG / CLEAR_DIALOG needed remapping for the new block/item IDs. [VV-LOG v1_21_6to1_21_7]

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773 — 1.21.9 / 1.21.10 (September 30 / October 7, 2025)

Gameplay headline

"The Copper Age" — copper golem mob, copper tools/armor (stone-tier, high enchantability), copper chests (with oxidation), shelves (all wood types), copper lanterns/chains/bars. Chat drafts persist. New game rules (portal control, mob spawn). MCWIKI 1.21.9

1.21.10: Five bug fixes from 1.21.9 (wind charge collision, TP chunk loading, piston/cobweb entity clip). Same protocol 773. MCWIKI 1.21.10

Protocol changes (772→773)

VV package: v1_21_7to1_21_9/ (Protocol1_21_7To1_21_9.java)

This is a notably large bump: movement encoding overhaul, explosion restructure, debug packet additions.

Entity velocity encoding change

• ADD_ENTITY: Entity initial velocity previously encoded as three signed shorts (velX, velY, velZ — each = velocity × 8000, clamped). Now encoded as LOW_PRECISION_VECTOR (a compact 3-component float vector type). VV translates: reads the old shorts, reconstructs the vector. [VV EntityPacketRewriter1_21_9.java:replaceClientbound(ADD_ENTITY)]
• SET_ENTITY_MOTION: Same change — shorts → LOW_PRECISION_VECTOR. [VV EntityPacketRewriter1_21_9.java:registerClientbound(SET_ENTITY_MOTION)]
• PLAYER_ROTATION: Gets two relative: boolean flags (one per axis). VV writes false for both when translating down. [VV EntityPacketRewriter1_21_9.java:registerClientbound(PLAYER_ROTATION)]

Explosion restructure

EXPLODE packet restructured: the explosion radius and affected-block count (previously sent inline) are now sourced from PROJECTILE_POWER's tracked state. VV emits the old-format explosion packet using values from LastExplosionPowerStorage. A new block_particles list field appended (VV writes count=0). [VV Protocol1_21_7To1_21_9.java:replaceClientbound(EXPLODE)]

New debug packets (clientbound play)

Four new debug visualisation packets added (likely tied to the game test framework):

• DEBUG_BLOCK_VALUE (0x1A)
• DEBUG_CHUNK_VALUE (0x1B)
• DEBUG_ENTITY_VALUE (0x1C)
• DEBUG_EVENT (0x1D)

And GAME_EVENT_TEST_HIGHLIGHT_POS (0x27): Highlight test positions in the world. [VV ClientboundPackets1_21_9.java]

All existing IDs shift up accordingly — packet count goes from 134 (0x85) in 772 to 139 (0x8A) in 773.

Configuration state changes

• CODE_OF_CONDUCT (0x13) added to serverbound Configuration packets (client accepts/rejects). VV cancels ACCEPT_CODE_OF_CONDUCT when translating down. [VV ServerboundConfigurationPackets1_21_9.java:0x09; Protocol1_21_7To1_21_9.java:cancelServerbound(ACCEPT_CODE_OF_CONDUCT)]

Debug sample subscription

DEBUG_SAMPLE_SUBSCRIPTION serverbound changed: from a single type: varint to a list count: varint + per-entry registry_id: varint. VV maps the new DEDICATED_SERVER_TICK_TIME subscription (id=0) back to the old TICK_TIME type (0). [VV Protocol1_21_7To1_21_9.java:registerServerbound(DEBUG_SAMPLE_SUBSCRIPTION)]

SET_DEFAULT_SPAWN_POSITION

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774 — 1.21.11 (December 9, 2025)

Gameplay headline

"Mounts of Mayhem" — nautilus (tameable aquatic mount), zombie nautilus (hostile), camel husk, parched (desert skeleton), zombie horseman. Spears (7 material tiers, jab + charge attacks, lunge enchantment). Nautilus armor. Netherite horse armor. Overhaul of dimension type and biome data (environment attributes system). MCWIKI 1.21.11

Protocol changes (773→774)

VV package: v1_21_9to1_21_11/ (Protocol1_21_9To1_21_11.java)

This is the most structurally significant bump of the 1.21 line from a proxy standpoint.

Packet rename

• HORSE_SCREEN_OPEN → MOUNT_SCREEN_OPEN (same ID 0x28; name change only reflects expanded mount support). VV registers a direct remap. [VV EntityPacketRewriter1_21_11.java:registerClientbound(HORSE_SCREEN_OPEN → MOUNT_SCREEN_OPEN)]

New entity type

• zombie_nautilus entity type added. New entity-data type zombieNautilusVariantType registered. [VV EntityPacketRewriter1_21_11.java:registerRewrites(), EntityTypes1_21_11]

Registry injection at FINISH_CONFIGURATION

VV injects two entirely new registries before the config-phase completes, so older servers' clients see them:

• zombie_nautilus_variant registry — VV synthesizes a single entry (minecraft:pale with temperate asset ID). [VV Protocol1_21_9To1_21_11.java:registerPackets(), appendClientbound(FINISH_CONFIGURATION)]
• timeline registry — an experimental feature allowing time-based behavior modifications. VV synthesizes entries from MAPPINGS.timelineRegistry(). [VV Protocol1_21_9To1_21_11.java:registerPackets()]

dimension_type registry overhaul (massive)

The dimension_type data format was significantly restructured — many fields extracted into a new attributes compound NBT sub-object. VV performs full field-level migration for each dimension type entry:

• fixed_time → has_fixed_time boolean
• has_raids → attributes/"gameplay/can_start_raid"
• piglin_safe → attributes/"gameplay/piglins_zombify" (inverted)
• respawn_anchor_works → attributes/"gameplay/respawn_anchor_works"
• ultrawarm → attributes/"gameplay/fast_lava" + "gameplay/water_evaporates"
• cloud_height → attributes/"visual/cloud_height" + synthesizes "visual/cloud_color": "#ccffffff"
• New fields added: skybox, cardinal_light, timelines list, attributes/"visual/sky_light_color", attributes/"visual/fog_start_distance", attributes/"visual/fog_end_distance", attributes/"audio/background_music", ambient cave sounds.

[VV Protocol1_21_9To1_21_11.java:registryDataRewriter dimension_type handler]

worldgen/biome registry overhaul

Biome registry entries similarly gain an attributes sub-object with all sound and visual properties migrated:

• effects.sky_color → attributes/"visual/sky_color" (suppressed for nether biomes)
• effects.water_fog_color → attributes/"visual/water_fog_color"
• effects.fog_color → attributes/"visual/fog_color"
• effects.music → attributes/"audio/background_music"
• effects.mood_sound/additions_sound/ambient_sound → attributes/"audio/ambient_sounds"
• effects.particle → attributes/"visual/ambient_particles"

[VV Protocol1_21_9To1_21_11.java:registryDataRewriter worldgen/biome handler]

New item components

• ATTACK_RANGE, USE_EFFECTS, MINIMUM_ATTACK_CHARGE, DAMAGE_TYPE1_21_11, PIERCING_WEAPON, KINETIC_WEAPON, SWING_ANIMATION, ZOMBIE_NAUTILUS_VARIANT1_21_11

[VV Protocol1_21_9To1_21_11.java:onMappingDataLoaded()]

Game time storage

VV adds GameTimeStorage to track absolute game time (needed for timeline-based behavior). [VV Protocol1_21_9To1_21_11.java:init()]

Serverbound: spear cancel

PLAYER_ACTION action ID 7 ("stab") added for spear jab — VV cancels these when downgrading. [VV EntityPacketRewriter1_21_11.java:registerServerbound(PLAYER_ACTION)]

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Proxy and ViaVersion translation impact

Bump	Translation cost	Key challenge
766→767	Low	Attribute UUID↔ID bidirectional map; PROJECTILE_POWER scalar; chat type holder
767→768	High	7 new clientbound packets (all IDs shift); 2 new serverbound; full item-component set rebuild; max-health tracking; chunk-load workaround for 1.21.2 clients
768→769	Medium	PICK_ITEM split; LEVEL_PARTICLES field insert; profile action enum extension
769→770	High	ADD_EXPERIENCE_ORB removal (XP orbs now ADD_ENTITY); message-index synthesis for chat; chat checksum stripping; test-framework packets cancelled; 20+ new item components including all mob-variant data
770→771	Medium	Dialog packet passthrough (play+config); sneak flag synthesis from PLAYER_INPUT; PLAYER_COMMAND action re-numbering; CHANGE_DIFFICULTY type conversion; dialog registry injection
771→772	Low	ID remapping only; dialog packet item rewriting
772→773	High	Entity velocity type change (LOW_PRECISION_VECTOR ↔ shorts) for ALL entities; explosion packet restructure; 5 new debug/test packets shifting all IDs; explosion power storage tracking
773→774	Very high	Full dimension_type field migration (many fields → attributes compound); full worldgen/biome field migration; two new registry types injected during config; new entity type + variant; spear action filtering

Proxy notes:

• Login state: LOGIN_FINISHED lost strict_error_handling (768). If a proxy injects it, strip on the way down.
• Configuration state: Dialog packets (CLEAR_DIALOG, SHOW_DIALOG) appear in both config and play states from 771 onward. Proxies must forward these in both states.
• CODE_OF_CONDUCT (config, 773): New serverbound; cancel when forwarding to 772 servers.
• BUNDLE_ITEM_SELECTED / CLIENT_TICK_END (768): Cancel toward 767 servers.
• Chunk-load (768): 1.21.2 clients need forced chunk unload before re-send; 1.21.3/1.21.4 don't.
• Item components: Every bump through 770 added or renamed component keys. A proxy doing item translation must track which component key set the connected client/server uses.
• dimension_type (774): By far the most complex registry translation in the 1.21 line — the field-level migration is large enough that ViaVersion devotes ~150 lines of registry rewriting code to it alone.