Problem statement
Matter 1.6 was released by the CSA on June 17, 2026, and a 1.6.1 maintenance update is expected to follow on the standard's regular cadence. Alongside the spec update itself, Matter 1.6 introduced the Groupcast cluster as a provisional feature, with certification targeted for a subsequent release. Groupcast is the mechanism by which a controller can address multiple devices simultaneously via a single IPv6 multicast message rather than a sequence of individual unicast commands.
The practical gap this closes is one of the most visible and long-standing annoyances in group-based smart home control: the "popcorn effect," where devices in a group respond one by one with perceptible delays between them. The Matter specification has supported basic group messaging since 1.0, but no major controller, including Home Assistant, has implemented it fully. HA currently manages Matter device groups by issuing sequential unicast commands through a helper group entity, which produces exactly the staggered behavior users experience and complain about.
Groupcast replaces the older approach with a proper one-to-many delivery model. A single command reaches all group members simultaneously, regardless of network size or topology complexity. For users with multiple lights in a room, a bank of switches, or motorized shades, this is the difference between a group that feels instantaneous and one that visibly rolls across the room. Implementing Groupcast support in HA as part of the 1.6.1 update positions Home Assistant as the first major open controller to deliver this experience natively, and sets a foundation for future work on group management, scenes, and bindings.
Community signals
WTH: Popcorn Effect with Matter switches, no Groupcast (HA "What the heck?!" month, Dec 2024)
A dedicated WTH post explicitly named the absence of Groupcast as the root cause of the popcorn effect in HA's Matter integration. A developer confirmed in a linked GitHub comment that group management support does not exist yet in the Matter server and is on the to-do list. The thread also clarified that command batching from Matter 1.3 does not help for native Matter devices, only for bridged ones.
→ https://community.home-assistant.io/t/wth-popcorn-effect-with-matter-switches-no-groupcast/802773
Light groups in Matter? (community.home-assistant.io, Aug 2025)
A user with six Matter light bulbs reports that using a helper group in HA results in only two bulbs coming on immediately while the others follow sequentially. The post explicitly compares this to the correct behavior they had with Zigbee groups, and asks whether Matter supports an equivalent. No native solution was available at the time.
→ https://community.home-assistant.io/t/light-groups-in-matter/922586
Eliminating the popcorn effect when toggling grouped Aqara lights in HA (Aqara Forum, Aug 2025)
A detailed community post documenting the popcorn effect specifically with Aqara Matter-over-Thread lights in HA, including workarounds users have attempted. The existence of a dedicated workaround thread confirms this is a consistent, cross-brand problem rather than a device-specific one.
→ https://forum.aqara.com/t/eliminating-the-popcorn-effect-when-toggling-grouped-aqara-lights-in-home-assistant/69312
Support Zigbee and Thread groups in HA (home-assistant/architecture, GitHub discussion)
An architecture-level discussion on how HA should model protocol-level light groups for Zigbee and Matter. Participants noted that HA's abstraction layer currently prevents efficient group messaging from being surfaced correctly, and that this is a known blind spot in how HA handles multi-device group control. The discussion highlights that solving this properly requires both server-side and HA-side work.
→ home-assistant/architecture#882
Matter 1.6 Groupcast confirmed as provisional, targeting 1.6.1 or later (Matter Alpha, Jun 2026)
An analysis of Matter 1.6's provisional features confirmed that the Groupcast cluster is drafted and in active development but not yet certifiable at the 1.6 release. It is explicitly identified as a candidate for Matter 1.6.1 or 1.7, making this opportunity directly tied to the next minor spec update.
→ https://www.matteralpha.com/industry-news/matter-1-6-provisional-features-future
Scope & Boundaries
In scope
- Update the HA Matter Server (matter.js) to Matter 1.6.1 when released
- Implement the Groupcast cluster on the controller side, enabling HA to send single multicast commands to Matter device groups over Thread and Wi-Fi
- Surface Matter group management in the HA UI so users can create and manage native Matter groups rather than relying on helper group entities
- Validate Groupcast behavior across multiple device brands and Thread network sizes
- Assess the interaction between Matter Groupcast and HA's existing light group entity model, and resolve any abstraction layer conflicts that prevent correct behavior
Not in scope
- Matter 1.7 or future spec work
- Groupcast support for non-Matter protocols (Zigbee, Z-Wave)
- Scenes or bindings as a full feature, though groundwork laid here feeds into that goal
- Cross-protocol group management unification (addressed as a separate opportunity)
Foreseen solution
wip
Risks & open questions
wip
Appetite
Medium - 3-4 weeks
Execution issues
No response
Decision log
Problem statement
Matter 1.6 was released by the CSA on June 17, 2026, and a 1.6.1 maintenance update is expected to follow on the standard's regular cadence. Alongside the spec update itself, Matter 1.6 introduced the Groupcast cluster as a provisional feature, with certification targeted for a subsequent release. Groupcast is the mechanism by which a controller can address multiple devices simultaneously via a single IPv6 multicast message rather than a sequence of individual unicast commands.
The practical gap this closes is one of the most visible and long-standing annoyances in group-based smart home control: the "popcorn effect," where devices in a group respond one by one with perceptible delays between them. The Matter specification has supported basic group messaging since 1.0, but no major controller, including Home Assistant, has implemented it fully. HA currently manages Matter device groups by issuing sequential unicast commands through a helper group entity, which produces exactly the staggered behavior users experience and complain about.
Groupcast replaces the older approach with a proper one-to-many delivery model. A single command reaches all group members simultaneously, regardless of network size or topology complexity. For users with multiple lights in a room, a bank of switches, or motorized shades, this is the difference between a group that feels instantaneous and one that visibly rolls across the room. Implementing Groupcast support in HA as part of the 1.6.1 update positions Home Assistant as the first major open controller to deliver this experience natively, and sets a foundation for future work on group management, scenes, and bindings.
Community signals
WTH: Popcorn Effect with Matter switches, no Groupcast (HA "What the heck?!" month, Dec 2024)
A dedicated WTH post explicitly named the absence of Groupcast as the root cause of the popcorn effect in HA's Matter integration. A developer confirmed in a linked GitHub comment that group management support does not exist yet in the Matter server and is on the to-do list. The thread also clarified that command batching from Matter 1.3 does not help for native Matter devices, only for bridged ones.
→ https://community.home-assistant.io/t/wth-popcorn-effect-with-matter-switches-no-groupcast/802773
Light groups in Matter? (community.home-assistant.io, Aug 2025)
A user with six Matter light bulbs reports that using a helper group in HA results in only two bulbs coming on immediately while the others follow sequentially. The post explicitly compares this to the correct behavior they had with Zigbee groups, and asks whether Matter supports an equivalent. No native solution was available at the time.
→ https://community.home-assistant.io/t/light-groups-in-matter/922586
Eliminating the popcorn effect when toggling grouped Aqara lights in HA (Aqara Forum, Aug 2025)
A detailed community post documenting the popcorn effect specifically with Aqara Matter-over-Thread lights in HA, including workarounds users have attempted. The existence of a dedicated workaround thread confirms this is a consistent, cross-brand problem rather than a device-specific one.
→ https://forum.aqara.com/t/eliminating-the-popcorn-effect-when-toggling-grouped-aqara-lights-in-home-assistant/69312
Support Zigbee and Thread groups in HA (home-assistant/architecture, GitHub discussion)
An architecture-level discussion on how HA should model protocol-level light groups for Zigbee and Matter. Participants noted that HA's abstraction layer currently prevents efficient group messaging from being surfaced correctly, and that this is a known blind spot in how HA handles multi-device group control. The discussion highlights that solving this properly requires both server-side and HA-side work.
→ home-assistant/architecture#882
Matter 1.6 Groupcast confirmed as provisional, targeting 1.6.1 or later (Matter Alpha, Jun 2026)
An analysis of Matter 1.6's provisional features confirmed that the Groupcast cluster is drafted and in active development but not yet certifiable at the 1.6 release. It is explicitly identified as a candidate for Matter 1.6.1 or 1.7, making this opportunity directly tied to the next minor spec update.
→ https://www.matteralpha.com/industry-news/matter-1-6-provisional-features-future
Scope & Boundaries
In scope
Not in scope
Foreseen solution
wip
Risks & open questions
wip
Appetite
Medium - 3-4 weeks
Execution issues
No response
Decision log