Vercel / Deployment

Vercel Python function cold start times suboptimal due to bundle bloat

Reduce Python function cold start latency on Vercel Serverless Functions — remove unused files from deployment bundle to improve invocation speed Includes evidence for Vercel troubleshooting demand.

Source-backed Last updated May 23, 2026 1 source Needs local verification

Category: Deployment
Error signature: FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files)
Quick fix: Check the build output, project root, and deployment platform configuration before redeploying.
Updated: May 23, 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 Vercel, 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

FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files) is a Vercel failure pattern reported for developers trying to reduce python function cold start latency on vercel serverless functions — remove unused files from deployment bundle to improve invocation speed. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

PR #16400 merged 2026-05-22 introduces shouldStripVendorFile, PYTHONDONTWRITEBYTECODE, UV_NO_INSTALLER_METADATA flags. Cold starts are critical for serverless billing — each extra second costs money. Commercial value: high — Vercel paying users affected by slow deployments. Category: Deployment matches Vercel.

Common causes

PR #16400 merged 2026-05-22 introduces shouldStripVendorFile, PYTHONDONTWRITEBYTECODE, UV_NO_INSTALLER_METADATA flags. Cold starts are critical for serverless billing — each extra second costs money. Commercial value: high — Vercel paying users affected by slow deployments. Category: Deployment matches Vercel.

Quick fixes

Confirm the exact error signature matches FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files).
Check the Vercel 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 FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files) exactly before applying the quick fix.
Compare the failing environment with Vercel 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 FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files) mean in Vercel?

FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files) indicates the workflow described by "Vercel Python function cold start times suboptimal due to bundle bloat" failed in a Deployment context. Start by confirming the exact signature and the component that emitted it.

What should I check first for FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files)?

Check whether this cause matches your environment: PR #16400 merged 2026-05-22 introduces shouldStripVendorFile, PYTHONDONTWRITEBYTECODE, UV_NO_INSTALLER_METADATA flags. Cold starts are critical for serverless billing — each extra second costs money. Commercial value: high — Vercel paying users affected by slow deployments. Category: Deployment matches Vercel.

Is the FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files) guidance source-backed?

The "Vercel Python function cold start times suboptimal due to bundle bloat" 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 FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files)?

For "Vercel Python function cold start times suboptimal due to bundle bloat", 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 FUNCTION_INVOCATION_TIMEOUT or slow cold start on Vercel Python functions due to unnecessary files in bundle (uv installer metadata, unused vendor files)?

For "Vercel Python function cold start times suboptimal due to bundle bloat", collect the failing Vercel command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.