Vertex AI / Claude / AI Coding Tools

Vertex AI Claude Provider Drops response_format — Structured Output Always Fails

Fix Vertex AI Claude provider silently dropping response_format field, causing structured JSON output failures Includes evidence for Vertex AI / Claude troubleshooting demand.

Source-backed Last updated May 13, 2026 1 source Needs local verification

Category: AI Coding Tools
Error signature: Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 13, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for Vertex AI / Claude, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

What this error means

Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review is a Vertex AI / Claude failure pattern reported for developers trying to fix vertex ai claude provider silently dropping response_format field, causing structured json output failures. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Sashiko issue #171: Vertex AI Claude provider (claude-sonnet-4-6 and claude-opus-4-6 in us-east5) drops response_format field in generate_claude(), causing Stage 1 AI review to always fail with 'failed to produce valid concerns array after 3 attempts'. Direct rawPredict calls with same credentials work fine — the bug is in the SDK layer not forwarding response_format to Vertex ClaudeRequest. 12 comments.

Common causes

When using Claude models through Google Vertex AI (not direct Anthropic API), the response_format field is silently dropped from requests. This causes any tool or application that expects structured JSON output (via response_format) to fail with parsing errors. The Vertex API endpoint itself works fine for free-form responses, making this a subtle integration bug that only surfaces with structured output requirements.
Sashiko issue #171: Vertex AI Claude provider (claude-sonnet-4-6 and claude-opus-4-6 in us-east5) drops response_format field in generate_claude(), causing Stage 1 AI review to always fail with 'failed to produce valid concerns array after 3 attempts'. Direct rawPredict calls with same credentials work fine — the bug is in the SDK layer not forwarding response_format to Vertex ClaudeRequest. 12 comments.

Quick fixes

Confirm the exact error signature matches Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review.
Check the Vertex AI / Claude account, local tool state, and provider configuration involved in the failing workflow.
Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

Verify the command, editor, extension, or API client that produced the error.
Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

Capture the exact error message and the command, editor action, or request that triggered it.
Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
Review the source evidence below and compare it with your environment.
Apply one change at a time and rerun the smallest failing action.
Keep the working fix documented for the team or deployment environment.

How to prevent it

Keep provider/tool configuration documented.
Record non-secret diagnostics such as tool version, provider name, model name, and command path.
Add a lightweight check before CI or production workflows depend on the tool.

Diagnostic flow for this page

Match Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review exactly before applying the quick fix.
Compare the failing environment with Vertex AI / Claude versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review mean in Vertex AI / Claude?

Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review indicates the workflow described by "Vertex AI Claude Provider Drops response_format — Structured Output Always Fails" failed in a AI Coding Tools context. Start by confirming the exact signature and the component that emitted it.

What should I check first for Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review?

Check whether this cause matches your environment: When using Claude models through Google Vertex AI (not direct Anthropic API), the response_format field is silently dropped from requests. This causes any tool or application that expects structured JSON output (via response_format) to fail with parsing errors. The Vertex API endpoint itself works fine for free-form responses, making this a subtle integration bug that only surfaces with structured output requirements.

Is the Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review guidance source-backed?

The "Vertex AI Claude Provider Drops response_format — Structured Output Always Fails" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review?

For "Vertex AI Claude Provider Drops response_format — Structured Output Always Fails", avoid applying "Compare the failing environment with a known working setup, then change one configuration value at a time." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging Stage 1 failed to produce valid 'concerns' array after 3 attempts — aborting review?

For "Vertex AI Claude Provider Drops response_format — Structured Output Always Fails", collect the failing Vertex AI / Claude command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.