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[FEATURE]: Support for Model Variants in (sub)agents #6645
Description
Feature hasn't been suggested before.
- I have verified this feature I'm about to request hasn't been suggested before.
Describe the enhancement you want to request
When having multiple variants of an model configured.
it would be good to have the agent config point to a specific model variant.
// Global Model Configuration
"anthropic/claude-sonnet-4-5": {
"name": "anthropic/claude-sonnet-4-5",
"variants": {
"thinking": {
"thinking": {
"type": "enabled",
"budget_tokens": 1600
},
"max_tokens": 2000
},
"fast": {
"thinking": {
"type": "disabled"
}
}
}
}would result in something like
---
description: Performs security audits and identifies vulnerabilities
mode: subagent
model: anthropic/claude-sonnet-4-5:fast
tools:
write: false
edit: false
---
You are a security expert. Focus on identifying potential security issues.
Analyze the provided code and identify vulnerabilities such as SQL injection,
XSS, or insecure dependency versions.when i use a config with variants an did not specify any it takes the default model but that seems to prefer thinking.
it errors with
{"message":"The model returned the following errors: messages.1.content.0.type: Expected `thinking` or `redacted_thinking`, but found `text`. When `thinking` is enabled, a final `assistant` message must start with a thinking block (preceeding the lastmost set of `tool_use` and `tool_result` blocks). We recommend you include thinking blocks from previous turns. To avoid this requirement, disable `thinking`. Please consult our documentation at https://docs.claude.com/en/docs/build-with-claude/extended-thinking"}. Received Model Group=anthropic/claude-4-5-sonnet
Available Model Group Fallbacks=Non
when i use a simpel model config
"anthropic/claude-4-5-sonnet": {
"name": "anthropic/claude-4-5-sonnet",
"options": {
"thinking": {
"type": "disabled"
}
}
},---
description: Performs security audits and identifies vulnerabilities
mode: subagent
tools:
write: false
edit: false
---it does work! it takes that model and performs the actions as the security auditor.
Activity
github-actions commentedon Jan 2, 2026
This issue might be a duplicate of existing issues. Please check:
Feel free to ignore if none of these address your specific case.
Blankf commentedon Jan 2, 2026
it seems the id field is it, i missed that i guess.
mjakl commentedon Jan 5, 2026
@Blankf can you elaborate how the
idfield works to setup thevariant? I'd also like to configure a model and a variant in my agent definition but couldn't figure out how to do that (without falling back to full model aliases).CasualDeveloper commentedon Jan 7, 2026
For anyone following this issue - there's now an active effort to properly implement agent-level variant configuration:
Both PRs add a
variantfield to agent config:{ "agent": { "security-auditor": { "model": "anthropic/claude-sonnet-4-5", "variant": "fast" } } }This addresses the original request - you can now configure which variant each agent uses by default, without needing model aliases or the
:variantsuffix syntax.The variant priority order is:
--variantorctrl+t)