# Fluid: How we built serverless servers

By Steven Van · 2025-07-28

Vercel's engineering writeup explains the custom Lambda tunnel behind Fluid compute, now handling 45 billion requests a week.

Vercel has published a behind-the-scenes account of how it built [Fluid compute](<https://creatorstoolbox.com/tools/vercel>), the serverless model it introduced in February. Because Vercel Functions run on AWS Lambda, which didn't support streaming responses, the team built its own secure TCP-based tunnel connecting each Lambda instance back to Vercel's infrastructure, sending HTTP responses back as a stream of packets instead of a single blob. That transport layer, built over more than two years, is what let Vercel add streaming, reduced cold starts, and its many-to-one scaling model on top of Lambda's simple request/response execution.

Fluid compute now runs alongside Active CPU pricing, introduced at Vercel Ship 2025, and together the two handle over **45 billion** requests a week, with some customers saving up to **95%** on compute costs and no charge for CPU time spent idle.

![Fluid compute allows for more efficient compute usage than traditional serverless](<https://assets.vercel.com/image/upload/contentful/image/e5382hct74si/3OWy1gLs16FQQEZeyuH8co/8bb14531ca780c8996c5470ea37467d2/traditional-serverless-vs-fluid-vercel-functions-desktop-light.png>)

Fluid compute allows for more efficient compute usage than traditional serverless

![Vercel](<https://www.google.com/s2/favicons?domain=vercel.com&sz=128>)

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[Original source](<https://vercel.com/blog/introducing-fluid-compute>)

[Read Fluid: How we built serverless servers on Creators Toolbox](<https://creatorstoolbox.com/blog/vercel-fluid-how-we-built-serverless-servers>)

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Canonical source: https://creatorstoolbox.com/blog/vercel-fluid-how-we-built-serverless-servers