How do I spawn a non-fast composer-2.5 Task subagent? Only composer-2.5-fast is accepted

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1

I’m trying to use regular Composer 2.5 (not fast) for small Task subagents, and I can’t find a way to do it.

This isn’t the Cursor Desktop “Agents” UI or an Agents folder workflow. I’m in the Cursor agent/CLI flow, where the parent agent dispatches work via the Task tool (subagent_type: generalPurpose, etc.), with an explicit model parameter.

I have tried passing this to Task for the model value:

  1. composer-2.5 → rejected
  2. composer-2.5[fast=false] → rejected
  3. composer-2.5-fast → works

Rejection looks like:

Invalid model selection “composer-2.5” / “composer-2.5[fast=false]”. Model could not be resolved to a valid subagent model.

Allowed Task model slugs in my environment currently include:

• claude-fable-5-thinking-high
• claude-opus-4-8-thinking-high
• claude-sonnet-5-thinking-high
• composer-2.5-fast
• cursor-grok-4.5-high
• gpt-5.6-sol-medium
• gpt-5.6-terra-medium

So the only Composer option exposed to Task is composer-2.5-fast.

Is non-fast composer-2.5 intentionally unavailable for Task subagents? If it is supported, what’s the correct model slug / syntax? (composer-2.5, composer-2.5[fast=false], something else?)

Thanks!

6

You’ve actually got the right syntax, it’s just in the wrong spot. composer-2.5[fast=false] (and composer-2.5[]) is valid, but that bracket syntax only works in a custom subagent’s frontmatter, not in the Task tool’s inline model parameter. The inline model value has to be one of the exact slugs it lists, and that list mirrors your model picker with a single variant per model family. Since Composer defaults to Fast, composer-2.5-fast is the only Composer entry it exposes, which is why bare composer-2.5 and the bracket form both get rejected there. Exposing all variants inline is a known limitation we’re tracking.

A few ways to get standard (non-fast) Composer 2.5 for your subagents:

  1. Define a custom subagent (cleanest, and it works in the CLI). Drop a file at .cursor/agents/composer-standard.md:
---
name: composer-standard
description: General-purpose work on standard (non-fast) Composer 2.5.
model: composer-2.5[fast=false]
---
Your subagent instructions here.

Then dispatch that subagent by name instead of generalPurpose with an inline model. The bracket syntax resolves correctly here. Docs: Subagents → Model configuration.

  1. Omit model so the subagent inherits the parent. Run your parent agent on standard Composer 2.5 and the subagents follow, no per-call model needed.

  2. Set Composer 2.5 to its standard (non-Fast) variant in your model picker, then start a fresh session. Once the picker has Composer 2.5 non-fast, composer-2.5 becomes an accepted inline Task slug too (the built-in composer-2.5-fast stays available).

Option 1 is your best bet if you want to pin it explicitly per subagent. Let me know if any of these get you unblocked!

8

Thanks for the context! Solution works, I opted for #3 because it fits my process :slight_smile: Thanks!