[BUG] Unsupported (?) model in agent config silently fails instead of erroring
Preflight Checklist
- [x] I have searched existing issues and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code
What's Wrong?
When I specify a model in agent configuration, certain model names are silently rejected—even if those same names work with the --model CLI flag. There are two failure modes:
Failure mode 1: Silent fallback (frontmatter agents)
With the main agent running Opus 4.6 + high effort, I created a subagent with this frontmatter:
---
name: player
description: The player agent is used to debug an agent bug
model: claude-opus-4-5
---
Answer only on which exact model version you run, then STOP.The agent spawns, but uses the main agent's config (Opus 4.6 with high effort) instead of the specified model. No warning, no error—just unexpected token burn.
Failure mode 2: Agent doesn't register (--agents flag)
When passing agents via CLI:
claude --agents '{
"player": {
"description": "Agent educator",
"prompt": "Tell me what model you are, then STOP",
"model": "claude-opus-4-5"
}
}'The agent simply doesn't exist. Asking to "spawn a player agent" results in:
What do you mean by "player agent"? Could you give me more context on what it should do?
No error about invalid model, no error about failed registration—the agent is silently dropped.
What Should Happen?
If a model name is invalid or unsupported for agents, Claude Code should error immediately with a clear message, e.g.:
Error: Model 'claude-opus-4-5' is not supported for agents. Supported models: claude-sonnet-4-6, claude-opus-4-6, ...
Or better: support the same models for agents that work with --model.
Error Messages/Logs
None—that's the problem. Both failures are completely silent.Steps to Reproduce
- Run
claude --model claude-opus-4-5(works fine) - Create an agent with
model: claude-opus-4-5in frontmatter, or via--agentsJSON - Observe: no error, but the model is ignored or the agent doesn't register
Claude Model
Opus
Is this a regression?
I don't know
Last Working Version
N/A
Claude Code Version
Latest
Platform
Anthropic API
Operating System
macOS
Terminal/Shell
Other
Additional Information
The core inconsistency: claude --model claude-opus-4-5 works, but model: claude-opus-4-5 in agent config doesn't. The same model name should either work everywhere or error everywhere.
6 Comments
Found 3 possible duplicate issues:
This issue will be automatically closed as a duplicate in 3 days.
🤖 Generated with Claude Code
Thanks for this report. Investigating
Thanks for the detailed report! We've identified the issue — agent config was only accepting model aliases (
opus,sonnet,haiku, etc.), not full model IDs likeclaude-opus-4-5. The runtime already handled full IDs fine; only the parse-time validation was overly strict.Fix should be in tomorrow's release. Once it lands,
model: claude-opus-4-5in frontmatter and--agentsJSON will work the same way as--model claude-opus-4-5does on the CLI.I should add that we can't be too strict about what we accept though; different configs require different model strings that can't be known at build time.
Fix landed in 2.1.74, thanks @wolffiex!
Edit: turns out the
--agentflag still doesn't work as expected. Though, the model version is correctly set, but the agent not recognised (even with short-alias). It's a bit weird, I could swear with the default alias it worked earlier. Opened a follow up https://github.com/anthropics/claude-code/issues/33513This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.