I’m seeing a sudden, extreme degradation in Vercel Function performance that began exactly at the start of my new billing cycle (Nov 21). Nothing changed in my code or infrastructure, yet function duration increased by 10×–40×, resulting in 132.52 GB-Hours billed this cycle vs 30.35 GB-Hours last cycle.
I am sharing the complete data below so Vercel staff or the community can help identify whether this is a Vercel-side issue.
1. Summary of the Issue
All my API routes suddenly became 10–40× slower starting Nov 21.
No code changes, no new queries, no new dependencies, no traffic spike.
The slowdown applies to every Node.js function except one.
As a result, function duration billing increased from $0 → $23.94, even though usage is lower than the previous cycle.
MongoDB performance logs show normal latency.
This strongly suggests a Vercel platform regression or environment change.
2. Route-Level Performance Comparison (Before vs After Nov 21)
Nov 21 → Dec 7 (current billing cycle)
(These durations are extremely abnormal for my app)
Route
Invocations
GB-Hours
P75 Duration
Error Rate
/api/messages/unread-count
32K
53.78
11s
52.8%
/api/connection-requests/received
33K
15.23
2.53s
0%
/api/notifications/unread-count
33K
14.23
2.4s
0%
/api/study-posts/[id]/increment-view
39K
9.78
1.78s
0%
/api/ad/random
39K
6.71
1.25s
0%
/api/study-posts/search
13K
5.87
2.56s
0%
/api/tags/recommended
10K
5.01
2.65s
0%
/api/users/connected-user
9K
4.33
2.73s
0%
/api/stream/webhook
17K
4.2
1.27s
0.1%
/api/sale-items/relevant
11K
2.36
1.68s
0%
Nov 5 → Nov 20 (previous period — SAME CODE)
(All functions were extremely fast and cheap)
Route
Invocations
GB-Hours
P75 Duration
Error Rate
/api/messages/unread-count
46K
6.64
69ms
4.3%
/api/connection-requests/received
47K
1.93
64ms
0%
/api/notifications/unread-count
47K
1.66
40ms
0%
/api/ad/random
65K
1.18
18ms
0%
/api/study-posts/search
18K
1.05
153ms
0%
/api/tags/recommended
14K
1.03
175ms
0%
/api/users/connected-user
13K
1
196ms
0%
/api/study-posts/[id]/increment-view
58K
0.67
20ms
0%
/api/sale-items/relevant
12K
0.47
151ms
0%
/api/feedback-images
8.4K
0.41
150ms
0%
3. Billing Comparison
Current Billing Cycle
Function Duration: 132.52 GB-Hours → $23.94
Function Invocations: 311.67K → $0.60
Build Minutes: $0.41
Observability base fee: $4.67
Total: $5.03 after $20 credit
Previous Billing Cycle
Function Duration: 30.35 GB-Hours → $0.00
Function Invocations: 870.66K → $0.00
Everything free under Pro plan credit
Total owed: $0
4. Why This Appears to Be a Vercel Issue
No code changes between cycles.
DB latency from MongoDB Atlas remains normal.
Functions that were consistently fast (20–150ms) suddenly take 1–11 seconds.
Slowdown affects all functions except one → unlikely to be DB-related.
Slowdown started exactly at billing cycle boundary (Nov 21 @ 9am).
GB-Hours increased 4.3× while traffic is lower.
This strongly suggests:
A runtime regression
A change in function scheduling or compute allocation
Unexpected throttling
A bug in duration metering
A change in Fluid Compute or cold start behavior
5. What I’ve Done Temporarily
To avoid runaway billing while debugging, I set:
export const maxDuration = 1;
on several endpoints to prevent long-hanging requests from inflating GB-Hours.
I may temporarily move API routes to a standalone Node server until I understand what’s going on.
6. My Questions for Vercel / Community
1. Did Vercel make any changes to Node.js function environments around Nov 21?
2. Are other users experiencing 10×–40× function slowdowns this billing cycle?
3. Could this be a regression in Fluid Compute or shared runtime allocation?
4. Is there a known issue where function duration is being overcounted?
5. How can I ensure my project isn’t being placed on degraded compute nodes?
6. Why do functions returning a single Mongo query suddenly take 2–11 seconds?
Thank You
This issue has a huge impact on my costs and app performance, so any insight from the Vercel team or other developers would be greatly appreciated.
My bills got 4-5 times bigger over night without change of code or traffic. Been trying to get an honest explanation from support without success. Switching to fluid compute won’t make a difference in my case. Migrated my most trafficked sites to other providers in the mean time. Its absurd!
Thanks for sharing. Glad you pointed out the tradeoff section from the Next 16 release notes. It might be related but we have to see what is causing your issue.
When did you upgrade to v16 in the project you shared? Does the increase in cost coincide with the update?
Correction: We’ve updated from 15 to 16 on the 28th of November but the most significant increase is on the 5th of December. On that day we only patched v16.0.5 to v16.0.7 because of the CVE-2025-55182 vulnerability.
Fluid compute might negate the increased costs but doesn’t explain it. I find it difficult to accept the increase when it’s not caused by increased traffic, builds or functionality.
And to be honest, it’s getting so ridiculous that I’m inclined to agree with Ahmedghribstranger and just move to another provider.
Hi @freekboon, thanks for sharing this information. It is taking longer because earlier it was confused for another issue, which was solved by enabling caching and fluid.
I’m still checking with the team. I’ll post an update here when I have.
Hey @freekboon – I just took a look at the project you reported and I think you might be running into this bug (specifically your […segments] routes). It looks like there’s a routing bug that causes these to lead to cache MISSes. I’m currently investigating the cause of this and will be working on a fix, but in the meantime, you could attempt to rename those files to a different value and see if it alleviates. I’ll update the above referenced GitHub issue once the underlying bug is fixed.
Thanks for the update and I will look into it. But we are not using Cache Components in this project. Is it possible for this bug to occur without using Cache Components?
1. Summary of the Issue
Nov 21 → Dec 7 (current billing cycle)
Current Billing Cycle
No code changes between cycles.
6. My Questions for Vercel / Community
Thank You