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Claude CodeUnverified

Fix Claude Code Opus 4.7 Bedrock API Error 400: 'invalid beta flag' on Linux and macOS

When using Claude Code v2.1.111 to access Claude Opus 4.7 via AWS Bedrock (bedrock-runtime endpoint), all API requests fail with 'API Error: 400' and 'invalid beta flag'. Root cause: Claude Code sends `anthropic_beta` flags in the request body, but Bedrock's Opus 4.7 endpoint only accepts them via the `anthropic-beta` HTTP header — any beta flags in the body cause a 400 rejection, even an empty array `[]`. Anthropic staff (@brenden) confirmed the bug and noted Opus 4.7 on bedrock-runtime was broken. Anthropic staff (@osulli) later confirmed 'Now fixed.' Three workarounds available: (1) switch to the Bedrock Mantle endpoint (official), (2) use the CLAUDE_CODE_EXTRA_BODY env var to overwrite the body and suppress beta flags (community, may not work for all), (3) upgrade Claude Code to the latest version which includes the server-side fix.

Symptoms

  • API Error: 400 with 'invalid beta flag' when using Claude Opus 4.7 via AWS Bedrock bedrock-runtime endpoint
  • Claude Code immediately fails on any prompt with 'API Error: 400 {"type":"error","request_id":"...","message":"invalid beta flag"}'
  • All Bedrock requests with Opus 4.7 selected as the model fail regardless of prompt content
  • Setting CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1 does not resolve the issue
  • The same configuration works with other Bedrock models but fails only with Opus 4.7

Error signatures

API Error: 400 {"type":"error","request_id":"req_*","message":"invalid beta flag"}
invalid beta flag
anthropic_beta

Possible causes

  • Claude Code v2.1.111 sends `anthropic_beta` flags in the request body when communicating with Bedrock, but Bedrock's Opus 4.7 endpoint only accepts beta flags via the `anthropic-beta` HTTP header and rejects any beta flags in the request body with a 400 error
  • Bedrock's Opus 4.7 endpoint has stricter validation than the standard Anthropic API — any `anthropic_beta` field in the JSON body (even an empty array `[]`) triggers 'invalid beta flag'
  • The `bedrock-runtime` endpoint does not support the same beta flag mechanism as `bedrock-mantle` for Opus 4.7
  • Disabling experimental betas via CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1 does not fully suppress the beta flag injection in the request body, so the error persists

Solutions

Upgrade Claude Code to Fixed Version (Permanent Fix, Recommended)

risk: lowofficialpublished

Anthropic staff (@osulli) confirmed the issue is 'Now fixed.' The fix was applied to the server-side Bedrock endpoint handling and is available in the latest Claude Code versions. Upgrading to the latest Claude Code release (currently v2.1.173 as of June 2026) permanently resolves the issue. This is the recommended long-term solution.

  1. Check current Claude Code version with `claude --version`
  2. If version is <= 2.1.111, upgrade to latest: `npm update -g @anthropic-ai/claude-code`
  3. Verify the new version is >= 2.1.112 (the fix was deployed shortly after v2.1.111 was identified as affected)
  4. Remove any workaround environment variables (CLAUDE_CODE_EXTRA_BODY, unset CLAUDE_CODE_USE_BEDROCK if switching back to runtime)
  5. Test Opus 4.7 with Bedrock bedrock-runtime endpoint to confirm the fix

Commands

claude --version
npm update -g @anthropic-ai/claude-code
claude -p "hello" --model "claude-opus-4-7"

Config examples

# Check current version:
claude --version
# Expected output (if affected): 2.1.111 or lower

# Upgrade:
npm update -g @anthropic-ai/claude-code

# Verify upgrade:
claude --version
# Expected output: 2.1.173 (or later)

Risks

  • Upgrading may introduce other regressions or behavior changes — test in a non-critical project first
  • Users pinned to a specific version for stability should test the new version in a sandbox before upgrading production environments
  • If you previously used the Mantle endpoint (Solution 1), ensure you reconfigure for bedrock-runtime after upgrading

Verification

  • Pre-check: Run `claude --version` → expect: version number. If <= 2.1.111, upgrade is needed
  • After upgrade: Run `claude --version` → expect: 2.1.173 or higher (confirm upgrade succeeded)
  • Run `claude -p "say hello" --model "claude-opus-4-7"` → expect: normal text response ('Hello!' or similar), NOT 'API Error: 400 … invalid beta flag'
  • Run `ANTHROPIC_LOG=debug claude -p "test" --model "claude-opus-4-7" 2>&1 | grep -i "error\|beta.flag"` → expect: no output (no errors or beta flag issues)
✓ 0 verified✕ 0 failed

Use CLAUDE_CODE_EXTRA_BODY Environment Variable to Suppress Beta Flags (Community Workaround)

risk: lowgithubpublished

Set the CLAUDE_CODE_EXTRA_BODY environment variable to inject a `thinking` field into the request body, which causes Claude Code to overwrite the entire body and omit the problematic `anthropic_beta` field. Note: this is a community-sourced workaround from @Menci; some users reported it did NOT work for them, so fall back to Solution 1 (Mantle) or Solution 3 (upgrade) if this fails.

  1. Set the CLAUDE_CODE_EXTRA_BODY environment variable with a JSON object containing a 'thinking' field
  2. Launch Claude Code as normal with Opus 4.7 selected
  3. This forces Claude Code to overwrite the request body, omitting the beta flags
  4. If the error persists, this workaround is not effective for your setup — switch to Solution 1 or 3
  5. Remove this workaround after upgrading to the fixed Claude Code version

Commands

export CLAUDE_CODE_EXTRA_BODY='{"thinking":{"type":"adaptive"}}'
claude -p "hello" --model "claude-opus-4-7"

Config examples

# Add to ~/.bashrc or ~/.zshrc for persistence:
export CLAUDE_CODE_EXTRA_BODY='{"thinking":{"type":"adaptive"}}'

# Or use inline for a single session:
CLAUDE_CODE_EXTRA_BODY='{"thinking":{"type":"adaptive"}}' claude -p "hello" --model "claude-opus-4-7"

# Troubleshooting: if this doesn't work, verify the env var is set:
echo $CLAUDE_CODE_EXTRA_BODY
# expected: {"thinking":{"type":"adaptive"}}

Risks

  • This workaround may break or behave differently after a Claude Code update that changes body construction logic
  • Forcing 'thinking' mode may affect model behavior or output quality (the model will use extended thinking)
  • Not all users confirmed this workaround works — @otayemre reported it did NOT resolve the issue for them
  • If CLAUDE_CODE_EXTRA_BODY is set long-term, it may conflict with future Claude Code features that use this mechanism legitimately

Verification

  • Pre-check: Run `echo $CLAUDE_CODE_EXTRA_BODY` → expect: {"thinking":{"type":"adaptive"}}
  • Run `CLAUDE_CODE_EXTRA_BODY='{"thinking":{"type":"adaptive"}}' claude -p "hello" --model "claude-opus-4-7"` → expect: normal text response, NOT 'API Error: 400 … invalid beta flag'
  • If error persists ('API Error: 400'), this workaround is not effective for your setup → use Solution 1 (Mantle endpoint) or Solution 3 (upgrade)
  • Run `ANTHROPIC_LOG=debug CLAUDE_CODE_EXTRA_BODY='{"thinking":{"type":"adaptive"}}' claude -p "test" --model "claude-opus-4-7" 2>&1 | grep -c "anthropic_beta"` → expect: 0 (zero occurrences, confirming beta flags are absent from body)
✓ 0 verified✕ 0 failed

Switch to Bedrock Mantle Endpoint (Official Workaround from Anthropic Staff)

risk: lowofficialpublished

Anthropic staff (@brenden) confirmed that while bedrock-runtime is broken for Opus 4.7, the bedrock-mantle endpoint still works correctly. Switch Claude Code to use the Mantle endpoint which routes through Anthropic's API with Bedrock-based model access. This is the most reliable workaround recommended by Anthropic.

  1. Unset the CLAUDE_CODE_USE_BEDROCK environment variable to disable the bedrock-runtime native path
  2. Set up Bedrock model access via the Mantle endpoint following the guide at https://code.claude.com/docs/en/amazon-bedrock#use-the-mantle-endpoint
  3. Configure AWS credentials with Bedrock InvokeModel permissions
  4. Restart Claude Code after switching to the Mantle endpoint
  5. Verify Opus 4.7 is selectable and functional by running a simple test prompt

Commands

unset CLAUDE_CODE_USE_BEDROCK
claude -p "hello" --model "claude-opus-4-7"

Config examples

# Unset the Bedrock native flag to use Mantle endpoint instead:
unset CLAUDE_CODE_USE_BEDROCK

# The Mantle endpoint routes through Anthropic API with Bedrock model access
# Follow setup: https://code.claude.com/docs/en/amazon-bedrock#use-the-mantle-endpoint

# Ensure AWS credentials are configured for Bedrock access:
aws configure list  # verify credentials are set

Risks

  • Mantle endpoint may have different pricing or latency characteristics than bedrock-runtime
  • Requires different AWS IAM permissions or setup configuration
  • If both CLAUDE_CODE_USE_BEDROCK is set AND Mantle is configured, Claude Code will attempt bedrock-runtime first and fail

Verification

  • Pre-check: Run `echo $CLAUDE_CODE_USE_BEDROCK` → should be empty (unset). If set, the native Bedrock path is still active
  • Run `claude -p "say hello" --model "claude-opus-4-7"` → expect: normal text response (e.g., 'Hello!'), NOT 'API Error: 400 … invalid beta flag'
  • Check Claude Code startup banner → expect: Opus 4.7 model listed without errors
  • Run `ANTHROPIC_LOG=debug claude -p "test" --model "claude-opus-4-7" 2>&1 | grep -i "mantle\|bedrock-mantle"` → expect: logs showing mantle endpoint usage, not bedrock-runtime
✓ 0 verified✕ 0 failed

Agent JSON

Canonical machine-readable representation of this issue:

{
  "issue_id": "cb1af2f3-cbef-4b1a-ba28-f572525166a4",
  "slug": "fix-claude-code-opus-4-7-bedrock-api-error-400-invalid-beta-flag-on-linux-and-macos-7n0ba7",
  "verification_status": "unverified",
  "canonical_json": "https://codekb.dev/v1/issues/fix-claude-code-opus-4-7-bedrock-api-error-400-invalid-beta-flag-on-linux-and-macos-7n0ba7"
}
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