claude-code - 💡(How to fix) Fix Feature: Version-pinned model parameter in Agent tool [2 comments, 3 participants]

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anthropics/claude-code#54888Fetched 2026-05-01 05:51:47
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Feature: Version-pinned model parameter in Agent tool

Current behavior

The Agent tool's model parameter only accepts generic names: "sonnet", "opus", "haiku". These resolve to the current versions at runtime.

Requested behavior

Allow specific model IDs: "claude-opus-4-5-20251101", "claude-sonnet-4-6", etc.

Use case

Multi-agent skills/plugins that spawn agents need version stability. When a new model version ships, all spawned agents silently upgrade — breaking prompts tuned for specific model behavior.

Example: a skill using model: "opus" for synthesis today gets Opus 4.7. Tomorrow it might get 4.8 with different reasoning patterns, breaking the aggregation logic.

Proposal

Accept both formats:

  • model: "sonnet" → latest (current behavior)
  • model: "claude-sonnet-4-6" → pinned version

extent analysis

TL;DR

Update the Agent tool to accept both generic model names and version-pinned model IDs for the model parameter.

Guidance

  • Modify the model parameter validation to allow for version-pinned IDs in the format "claude-<model>-<version>".
  • Update the model resolution logic to handle both generic names and version-pinned IDs, ensuring that the correct model version is used.
  • Consider adding input validation to ensure that the provided version-pinned ID is valid and exists.
  • Document the new format for the model parameter to inform users of the change.

Example

// Example model resolution function
function resolveModel(modelId) {
  if (modelId.includes('-')) { // Version-pinned ID
    const [_, model, version] = modelId.split('-');
    return getModelByVersion(model, version);
  } else { // Generic name
    return getLatestModel(modelId);
  }
}

Notes

The implementation details may vary depending on the existing codebase and model management system.

Recommendation

Apply workaround by updating the Agent tool to accept version-pinned model IDs, as this provides the necessary version stability for multi-agent skills and plugins.

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claude-code - 💡(How to fix) Fix Feature: Version-pinned model parameter in Agent tool [2 comments, 3 participants]