Vertex AI rejects ~2MB requests with 413 Prompt is too long error

What this error means

Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long is a Anthropic API failure pattern reported for developers trying to fix incorrect 413 rejection of payloads well under 32mb limit on anthropic claude via vertex ai. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue anthropics/anthropic-sdk-python#1028 by abhiwebshar (Sep 7 2025). Payloads as small as ~2MB consistently rejected with 413 error despite documented 32MB limit. Comprehensive root cause analysis in comments reveals Vertex AI misreports rate limit violations (429) as payload-size errors (413), specifically for Citations API format. Multiple regions affected. High value as it blocks legitimate large-context usage of Claude Sonnet 4 via enterprise Vertex AI deployment.

Common causes

• GitHub issue anthropics/anthropic-sdk-python#1028 by abhiwebshar (Sep 7 2025). Payloads as small as ~2MB consistently rejected with 413 error despite documented 32MB limit. Comprehensive root cause analysis in comments reveals Vertex AI misreports rate limit violations (429) as payload-size errors (413), specifically for Citations API format. Multiple regions affected. High value as it blocks legitimate large-context usage of Claude Sonnet 4 via enterprise Vertex AI deployment.

Quick fixes

1. Confirm the exact error signature matches Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long.
2. Check the Anthropic API account, local tool state, and provider configuration involved in the failing workflow.
3. 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

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. 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.

Sources checked

• https://github.com/anthropics/anthropic-sdk-python/issues/1028

Evidence note: GitHub issue anthropics/anthropic-sdk-python#1028 by abhiwebshar (Sep 7 2025). Payloads as small as ~2MB consistently rejected with 413 error despite documented 32MB limit. Comprehensive root cause analysis in comments reveals Vertex AI misreports rate limit violations (429) as payload-size errors (413), specifically for Citations API format. Multiple regions affected. High value as it blocks legitimate large-context usage of Claude Sonnet 4 via enterprise Vertex AI deployment.

Related errors

• Anthropic API

FAQ

What should I check first?

Start with the exact Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Anthropic API workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long.