Hey @coreprocess, yes, this is intentional. Custom models you add yourself (or anything routed through your own API key) are deliberately left out of the explicit subagent model list, so a subagent can’t be pinned to one via the Task tool or a model: field. That’s why the frontmatter definition falls back to the parent’s model and force-default-model has no effect.
The supported way to run a subagent on a custom model is the one you found: select it in the parent chat and use model: inherit (or leave model unset). Subagents inherit the parent’s model, so they do genuinely run on your custom model there, not a different one.