Anthropic API / Anthropic API

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

Fix incorrect 413 rejection of payloads well under 32MB limit on Anthropic Claude via Vertex AI Includes evidence for Anthropic API troubleshooting demand.

Source-backed Last updated May 19, 2026 1 source Needs local verification

Category: Anthropic API
Error signature: Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 19, 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 Anthropic API, 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

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

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.
Check the Anthropic API 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 Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long exactly before applying the quick fix.
Compare the failing environment with Anthropic API 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 Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long mean in Anthropic API?

Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long indicates the workflow described by "Vertex AI rejects ~2MB requests with 413 Prompt is too long error" failed in a Anthropic API context. Start by confirming the exact signature and the component that emitted it.

What should I check first for Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long?

Check whether this cause matches your environment: 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.

Is the Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long guidance source-backed?

The "Vertex AI rejects ~2MB requests with 413 Prompt is too long error" 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 Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long?

For "Vertex AI rejects ~2MB requests with 413 Prompt is too long error", 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 Error code: 413 — Request exceeds maximum allowed bytes. The maximum request size is 32 MB; Prompt is too long?

For "Vertex AI rejects ~2MB requests with 413 Prompt is too long error", collect the failing Anthropic API command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.