Vercel Bun Runtime Adds Large Functions and Extended Max Duration.

Vercel is giving developers substantially more room to run demanding backend code with Bun. The company’s Functions platform now supports Bun packages as large as 5GB uncompressed and execution times of up to 30 minutes, removing two constraints that previously pushed heavier workloads toward Node.js or Python.

The changes, detailed in Vercel’s official changelog, bring two existing beta capabilities to the Bun runtime: large functions and extended maximum duration. Both require Vercel’s Fluid compute architecture to be enabled.

This is a sizable increase. Large functions raise the normal uncompressed package limit from 250MB to 5GB, a twentyfold expansion. Extended duration raises the generally available ceiling from 800 seconds, or 13 minutes and 20 seconds, to 1,800 seconds, or 30 minutes, for Pro and Enterprise teams.

The package-size change concerns the deployed function and its dependencies, rather than the size of an incoming request payload. That distinction matters for applications that rely on large libraries, generated assets, binaries or other dependencies that cannot fit comfortably inside the standard 250MB limit.

Longer execution times address a separate bottleneck. Developers can now use Bun for jobs that need more than 800 seconds to complete, provided the work still fits within the new 30-minute ceiling. Potential use cases include document processing, data transformation, report generation and multi-step AI operations. Vercel has not positioned the update as a replacement for indefinite background workers, but it gives teams more flexibility before they need to move a task into a separate queue or compute service.

The practical significance is parity. These two betas were previously available only to functions running on Node.js and Python. Teams adopting Bun for its runtime performance and JavaScript tooling no longer have to switch runtimes solely because a function has a large dependency bundle or needs additional processing time.

Access depends on when a project was created. New projects are enrolled in the large functions beta automatically. Existing projects created before July 2026 must add the following environment variable in their project settings and redeploy:

VERCEL_SUPPORT_LARGE_FUNCTIONS=1

Durations above 800 seconds are configured per function in vercel.json; they are not applied as a project-wide default. Vercel provides the following pattern for assigning a 30-minute limit to a specific function:

{
  "$schema": "https://openapi.vercel.sh/vercel.json",
  "functions": {
    "server.ts": {
      "maxDuration": 1800
    }
  }
}

That per-function model should help teams limit longer execution windows to endpoints that genuinely require them. It also makes migration more deliberate, since increasing a timeout does not automatically change every function in the project.

There are still important qualifications. Large functions and extended duration remain beta features, Fluid compute must be active, and the 1,800-second option is limited to Pro and Enterprise teams. Developers should also consider the operational and usage implications of running functions for longer periods rather than treating the expanded ceiling as a default.

For builders already using Bun on Vercel, however, the update removes two concrete deployment constraints. It widens the range of backend work that can stay inside the same project and runtime, without requiring a rewrite simply to accommodate a bigger package or a longer-running task.

What are Vercel Bun runtime large functions and extended max duration?

They are two beta capabilities for Vercel Functions using Bun. Large functions increase the uncompressed package limit from 250MB to 5GB, while extended max duration allows eligible functions to run for up to 1,800 seconds.

Which Vercel plans can use the 30-minute execution limit?

The extended 1,800-second maximum is available to Pro and Enterprise teams. Fluid compute must be enabled, and durations above 800 seconds must be configured for each function in vercel.json.

Do existing projects receive large Bun functions automatically?

New projects are enrolled in the large functions beta automatically. Projects created before July 2026 must add VERCEL_SUPPORT_LARGE_FUNCTIONS=1 as an environment variable and then redeploy.