Claude Code / AI Coding Tools

Claude Code Subagents Fail on Vertex AI (Cowork) — Model Routing Hardcoded to Anthropic API Format

Fix Claude Code subagents failing on Vertex AI / Cowork deployment with Anthropic API format error Includes evidence for Claude Code troubleshooting demand.

Source-backed Last updated May 12, 2026 1 source Needs local verification

Category: AI Coding Tools
Error signature: All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens
Quick fix: Check the build output, project root, and deployment platform configuration before redeploying.
Updated: May 12, 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 Claude Code, 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

All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens is a Claude Code failure pattern reported for developers trying to fix claude code subagents failing on vertex ai / cowork deployment with anthropic api format error. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Official Claude Code issue #58274 (2026-05-12) reports all subagent types fail on Cowork/Vertex AI (3P) deployment. Subagents hardcoded to Anthropic API format model claude-haiku-4-5-20251001 are rejected. Main session with Opus 4.6 works fine.

Common causes

Enterprise users deploying Claude Code via Vertex AI (3P) find all subagent types completely non-functional. The main session works but every subagent attempt fails before token consumption. Critical for enterprise adopters paying for Vertex AI integration.
Official Claude Code issue #58274 (2026-05-12) reports all subagent types fail on Cowork/Vertex AI (3P) deployment. Subagents hardcoded to Anthropic API format model claude-haiku-4-5-20251001 are rejected. Main session with Opus 4.6 works fine.

Quick fixes

Confirm the exact error signature matches All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens.
Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
Check the build output, project root, and deployment platform configuration before redeploying.

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 All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens exactly before applying the quick fix.
Compare the failing environment with Claude Code 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 All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens mean in Claude Code?

All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens indicates the workflow described by "Claude Code Subagents Fail on Vertex AI (Cowork) — Model Routing Hardcoded to Anthropic API Format" 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 All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens?

Check whether this cause matches your environment: Enterprise users deploying Claude Code via Vertex AI (3P) find all subagent types completely non-functional. The main session works but every subagent attempt fails before token consumption. Critical for enterprise adopters paying for Vertex AI integration.

Is the All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens guidance source-backed?

The "Claude Code Subagents Fail on Vertex AI (Cowork) — Model Routing Hardcoded to Anthropic API Format" 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 All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens?

For "Claude Code Subagents Fail on Vertex AI (Cowork) — Model Routing Hardcoded to Anthropic API Format", avoid applying "Check the build output, project root, and deployment platform configuration before redeploying." 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 All subagent types fail on Cowork — model routing hardcoded to claude-haiku-4-5-20251001 (Anthropic API format), rejected before consuming any tokens?

For "Claude Code Subagents Fail on Vertex AI (Cowork) — Model Routing Hardcoded to Anthropic API Format", collect the failing Claude Code command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.