Anthropic API / Anthropic API

Anthropic Vertex AI Incorrectly Rejects ~2MB Requests with 413 'Prompt Is Too Long' When Limit Is 32MB

Fix Anthropic Vertex AI 413 error rejecting legitimate payloads under 32MB; differentiate between real prompt length limits vs incorrect rate-limit misreporting as 413 Includes evidence for Anthropic API troubleshooting demand.

Source-backed Last updated May 22, 2026 1 source Needs local verification

Category: Anthropic API
Error signature: Error code: 413 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit)
Quick fix: Reduce request pressure, check quota or plan limits, and retry with backoff instead of immediate repeated requests.
Updated: May 22, 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 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit) is a Anthropic API failure pattern reported for developers trying to fix anthropic vertex ai 413 error rejecting legitimate payloads under 32mb; differentiate between real prompt length limits vs incorrect rate-limit misreporting as 413. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub Issue #1028 on anthropics/anthropic-sdk-python (opened Sep 8, 2025). Author found Vertex AI incorrectly maps Citations API rate limit violations (429) to 413 payload errors. Payloads of 147KB–2MB are rejected with 'Request exceeds the maximum allowed number of bytes'. Root cause: error misreporting at the Vertex AI layer, not an actual payload size issue. Maps to 'Anthropic API' as the error originates from Anthropic's cloud-serving channel via Vertex AI. High value because document processing workloads in enterprise are completely blocked.

Common causes

GitHub Issue #1028 on anthropics/anthropic-sdk-python (opened Sep 8, 2025). Author found Vertex AI incorrectly maps Citations API rate limit violations (429) to 413 payload errors. Payloads of 147KB–2MB are rejected with 'Request exceeds the maximum allowed number of bytes'. Root cause: error misreporting at the Vertex AI layer, not an actual payload size issue. Maps to 'Anthropic API' as the error originates from Anthropic's cloud-serving channel via Vertex AI. High value because document processing workloads in enterprise are completely blocked.

Quick fixes

Confirm the exact error signature matches Error code: 413 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit).
Check the Anthropic API account, local tool state, and provider configuration involved in the failing workflow.
Reduce request pressure, check quota or plan limits, and retry with backoff instead of immediate repeated requests.

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 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit) 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 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit) mean in Anthropic API?

Error code: 413 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit) indicates the workflow described by "Anthropic Vertex AI Incorrectly Rejects ~2MB Requests with 413 'Prompt Is Too Long' When Limit Is 32MB" 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 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit)?

Check whether this cause matches your environment: GitHub Issue #1028 on anthropics/anthropic-sdk-python (opened Sep 8, 2025). Author found Vertex AI incorrectly maps Citations API rate limit violations (429) to 413 payload errors. Payloads of 147KB–2MB are rejected with 'Request exceeds the maximum allowed number of bytes'. Root cause: error misreporting at the Vertex AI layer, not an actual payload size issue. Maps to 'Anthropic API' as the error originates from Anthropic's cloud-serving channel via Vertex AI. High value because document processing workloads in enterprise are completely blocked.

Is the Error code: 413 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit) guidance source-backed?

The "Anthropic Vertex AI Incorrectly Rejects ~2MB Requests with 413 'Prompt Is Too Long' When Limit Is 32MB" 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 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit)?

For "Anthropic Vertex AI Incorrectly Rejects ~2MB Requests with 413 'Prompt Is Too Long' When Limit Is 32MB", avoid applying "Reduce request pressure, check quota or plan limits, and retry with backoff instead of immediate repeated requests." 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 - Prompt is too long (when payload is only ~2MB, well under documented 32MB limit)?

For "Anthropic Vertex AI Incorrectly Rejects ~2MB Requests with 413 'Prompt Is Too Long' When Limit Is 32MB", 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.