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Subscriptions

subscriptions/listen belongs to protocol revision 2026-07-28; see Protocol versions. Handshake-era clients keep using the HTTP GET stream and resources/subscribe, which the same server still answers.

subscriptions/listen replaces the HTTP GET stream and resources/subscribe. The client opens a long-lived POST whose response stream carries the notification types it asked for; the server acknowledges first with notifications/subscriptions/acknowledged, reporting the subset it agreed to honour.

The notification bus

Delivery needs a bus, because the process that publishes and the process holding the stream open are often not the same one:

use Mcp\Server\Subscription\InMemoryNotificationBus;
use Mcp\Server\Subscription\Psr16NotificationBus;

// stdio, or a persistent runtime where the whole server is one process
->setNotificationBus(new InMemoryNotificationBus())

// PHP-FPM: the publisher and the stream are different workers
->setNotificationBus(new Psr16NotificationBus($cache))

Registry changes (registerTool(), unregisterPrompt(), …) are published automatically. Anything else — notifications/resources/updated above all — is published by the application:

$bus->publish(new ResourceUpdatedNotification('file:///project/config.json'));

How long a stream lives

Builder::setSubscriptionLifetime() bounds how long a stream is held before the server closes it gracefully. The real ceiling is the runtime's: under PHP-FPM a stream cannot outlive max_execution_time. Pass 0 for "until the client or the runtime ends it".