Amazon Bedrock Grok 4.6 is routed through Mantle and fails with "The model does not exist"

[mclermont0]

OpenCode Desktop lists Amazon Bedrock Grok 4.6 (xai.grok-4.6) but invoking it fails:

AI_APICallError: The model 'xai.grok-4.6' does not exist

Changing the cache ID to us.xai.grok-4.6 still fails while OpenCode keeps using the Mantle adapter:

@ai-sdk/amazon-bedrock/mantle
https://bedrock-mantle.${AWS_REGION}.api.aws/openai/v1

That same profile works through native Bedrock Runtime:

aws bedrock-runtime converse --model-id us.xai.grok-4.6

Grok 4.3 works on Mantle. Grok 4.6 requires native Bedrock (@ai-sdk/amazon-bedrock) plus an inference profile (us.xai.grok-4.6 or global.xai.grok-4.6).

Expected: Use native Bedrock Runtime for Grok 4.6, or only list it if Mantle actually supports it.

[github-actions]

This issue might be a duplicate of or related to existing issues. Please check:

• [BUG]: Bedrock Mantle models unreachable on v2 — ${AWS_REGION} in base URL is never substituted #40075: Bedrock Mantle models unreachable on v2 — ${AWS_REGION} in base URL is never substituted (similar Bedrock Mantle routing issue affecting OpenAI-compatible models)