Is Substrate sold separately from Czar?

No. Substrate is the platform inside the Czar appliance, and it ships as part of the appliance subscription. There is no software-only Substrate, no platform fee alongside the hardware, and no per-service or per-model pricing. The subscription for the configured appliance is one line covering the hardware, the platform license, and sustainment, fixed for the term, and Substrate is what the platform license refers to.

The reason is not commercial convenience. Substrate's integrity model depends on being inside the appliance, and separating the two would remove the properties that make the platform worth running.

Why the platform and the appliance are one thing

Substrate's strongest claims rest on the appliance. The software image is sealed, signed, and read-only. Each node attests what it is running before it joins a Grid or takes work. Watchman verifies the image and the enclosure's tamper indicators continuously. The provenance record covers integration, sealing, and software load for every node. None of these properties survive on hardware Element 31 did not seal.

The posture claims rest on it too. No default path out, declared routes only, nothing leaving the building: these are enforceable because the platform runs in an enclosure whose network behavior is known and whose software is verified. On general-purpose servers with unknown software alongside, the site would have to take the claims on faith. On Czar, the site can check them.

So Substrate is not sold separately for the same reason a safety system is not sold as a schematic. The value is in the sealed, verified, running thing.

What the subscription covers

One line, fixed for the term, for the configured appliance. Hardware: the Czar or the Czar Grid, configured for the caller list the site provided. Platform license: all seven Substrate services, every model the site runs, every adapter it trains, with no usage metering. Sustainment: signed updates published to the portal for the customer to bring in, rollback to the previous signed release, and customer-initiated support through the portal.

There is no direct purchase of the appliance; the subscription is the one commercial form. There is nothing to add on for Retrieval or Adaptation, and nothing that charges by call, by caller, or by model. A site that uses one service and a site that uses all seven pay the same for the same configured appliance.

Czar Chassis and Czar Grid

Czar Chassis is Czar shipped by a robot vendor under the vendor's own name. It is the same appliance with the same Substrate inside. The commercial relationship may run through the vendor, but the platform is not separated from the hardware there either; the vendor's customer receives the sealed appliance with Substrate in it.

A Czar Grid is several Czars joined as one pool for a facility. The subscription covers the configured set. When a site adds a Czar to the Grid because its caller list has grown, the configured appliance grows and the subscription reflects that. No platform fee appears, because there is no platform fee to appear.

What this means when evaluating Substrate

A site evaluating the platform does not need to price software and hardware separately, compare license tiers, or model usage. It needs to describe its callers, their latency budgets, and the posture it wants, and the result is a configured appliance with Substrate inside it on one line. The appliance itself is described at e31.io/czar and e31.io/czar-grid; the platform is described here, starting at /platform. Design-partner intake is not yet open.