[BUG] Intermittent Task/subagents fail with API Error: 400 The provided model identifier is invalid while main agent succeeds (Bedrock)

# Intermittent Task/Subagent failure: `400 The provided model identifier is invalid` (Bedrock)

## Summary
When running Claude Code with AWS Bedrock enabled, `Task` subagents fail intermittently (~2 runs out of 3) with a 400 error.

## Error
```text
API Error: 400 The provided model identifier is invalid
invalid model: us.anthropic.claude-sonnet-4-5-20250929-v1:0
subagent failed after 3 attempts

Expected

Subagents invoked via Task should reliably use the same provider/model configuration as the parent run, and should not fall back to an invalid default model identifier.

Configuration (env + settings.json)

Environment variables

CLAUDE_CODE_USE_BEDROCK=1
CLAUDE_PROVIDER=bedrock
BEDROCK_MODEL_ID=anthropic.claude-3-5-sonnet

AWS_REGION=eu-west-3
ANTHROPIC_MODEL=eu.anthropic.claude-haiku-4-5-20251001-v1:0
ANTHROPIC_SMALL_FAST_MODEL=eu.anthropic.claude-sonnet-4-5-20250929-v1:0
ANTHROPIC_DEFAULT_HAIKU_MODEL=eu.anthropic.claude-haiku-4-5-20251001-v1:0

settings.json (as written)

{
  "env": {
    "AWS_ACCESS_KEY_ID": "${AWS_ACCESS_KEY_ID}",
    "AWS_SECRET_ACCESS_KEY": "${AWS_SECRET_ACCESS_KEY}",
    "CLAUDE_CODE_USE_BEDROCK": "1",
    "AWS_REGION": "${AWS_REGION}",
    "ANTHROPIC_MODEL": "${ANTHROPIC_MODEL}",
    "ANTHROPIC_SMALL_FAST_MODEL": "${ANTHROPIC_SMALL_FAST_MODEL}",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "${ANTHROPIC_DEFAULT_HAIKU_MODEL}",
    "CLAUDE_CODE_MAX_OUTPUT_TOKENS": "50000",
    "MAX_THINKING_TOKENS": "1024"
  },
  "permissions": {
    "allow": [
      "Bash(dir:*)",
      "Bash(cat:*)",
      "Bash(find:*)",
      "Bash(nul)",
      "Bash(findstr:*)",
      "Bash(git diff:*)",
      "Bash(git grep:*)"
    ],
    "deny": [],
    "ask": []
  }
}

Note

I’m not explicitly selecting us.anthropic.claude-sonnet-4-5-20250929-v1:0 anywhere; it appears as a fallback/default during Task subagent execution.

Question

Will the Bedrock model/region configuration issue be fixed in the next release? It’s mentioned in several issues.