feat(streams): add WebSocket capability gate by alangenfeld · Pull Request #3764 · vercel/workflow

alangenfeld · 2026-08-24T21:00:38Z

Summary & Motivation

WORKFLOW_STREAMS_TRANSPORT=ws advertises client support for workflow-stream-ws/v1 on stream writes; anything else keeps HTTP. It's a capability signal only — the server decides each upgrade, so there's no version or tenant-policy heuristic on the client side.

Test Plan

Unit tests for the gate's accepted values; typecheck, build, and lint pass locally.

changeset-bot · 2026-08-24T21:00:44Z

🦋 Changeset detected

Latest commit: 2802678

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 17 packages

Name	Type
@workflow/world-vercel	Patch
@workflow/cli	Patch
@workflow/core	Patch
@workflow/web	Patch
workflow	Patch
@workflow/world-testing	Patch
@workflow/builders	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/vitest	Patch
@workflow/web-shared	Patch
@workflow/astro	Patch
@workflow/nest	Patch
@workflow/rollup	Patch
@workflow/sveltekit	Patch
@workflow/vite	Patch
@workflow/nuxt	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

vercel · 2026-08-24T21:00:56Z

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 24, 2026 10:12pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 24, 2026 10:12pm
example-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-astro-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-express-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-hono-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-python-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-vite-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-docs	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-swc-playground	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-tarballs	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-web	Ready	Preview, v0	Aug 24, 2026 10:12pm

github-actions · 2026-08-24T21:01:00Z

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

promiseAllWorkflow | wrun_41M0TX7FF20GG2M6QX48T5JWGT | 🔍 observability
sleepingWorkflow | wrun_41M0TX86Y30GPBKATRGM7X9EC9 | 🔍 observability
parallelSleepWorkflow | wrun_41M0TX87SC0GKZM69Y147RPHEQ | 🔍 observability
nullByteWorkflow | wrun_41M0TX8F6M0GPBQ04J6CEJJRRX | 🔍 observability
cancelRun - cancelling a running workflow | wrun_41M0TXDF4D0GZFFYPPSH62NVHZ | 🔍 observability
cancelRun via CLI - cancelling a running workflow | wrun_41M0TXDHKQ0GYBE6FPA5CSEF60 | 🔍 observability
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0TXDQZT0GPFWKP2Q3WDVKY5 | 🔍 observability
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0TXEAVK0GH337JRM92DR4HH | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0TXKA8N9P9BEVE5K8MVYADK
promiseAllWorkflow | wrun_41M0TX7FF20GG2M6QX48T5JWGT
sleepingWorkflow | wrun_41M0TX86Y30GPBKATRGM7X9EC9
parallelSleepWorkflow | wrun_41M0TX87SC0GKZM69Y147RPHEQ
nullByteWorkflow | wrun_41M0TX8F6M0GPBQ04J6CEJJRRX
cancelRun - cancelling a running workflow | wrun_41M0TXDF4D0GZFFYPPSH62NVHZ
cancelRun via CLI - cancelling a running workflow | wrun_41M0TXDHKQ0GYBE6FPA5CSEF60
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0TXDQZT0GPFWKP2Q3WDVKY5
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0TXEAVK0GH337JRM92DR4HH

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

cancelRun via CLI - cancelling a running workflow (nextjs-turbopack)
concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack)
positive startIndex (skips first chunk) (fastify)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

33 infra events

cold-start-warmup · suite warmup (python) · at 22:13:34Z · abandoned wrun_41M0TX8DHV0GSYBXMYS5Q5FYT5 · (+7 more)
run-pickup-stall · nullByteWorkflow (python) · at 22:13:51Z · abandoned wrun_41M0TXC2M10GTK2DE8JRD2FE44
run-pickup-stall · sleepingWorkflow (python) · at 22:13:51Z · abandoned wrun_41M0TXC2KY0GG7XGYNTPGSCFKK
run-pickup-stall · promiseAllWorkflow (python) · at 22:13:51Z · abandoned wrun_41M0TXC2KR0GM1YEC3F36CY6SS
run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:51Z · abandoned wrun_41M0TXC2KY0GG7XGYNTPGSCFKM
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:51Z · abandoned wrun_41M0TXC32G0GNZJJ5H7G8RRACH
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:24Z · abandoned wrun_41M0TXD35F0GPENTKC9NHY5V2Z
run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:52Z · abandoned wrun_41M0TXDYA10GSD3163S3QXWRN7
run-pickup-stall · promiseAllWorkflow (python) · at 22:14:52Z · abandoned wrun_41M0TXDYA40GHDWN0RG7R389D7
run-pickup-stall · sleepingWorkflow (python) · at 22:14:52Z · abandoned wrun_41M0TXDY630GMA7GSNVGJS0RK9
run-pickup-stall · nullByteWorkflow (python) · at 22:14:52Z · abandoned wrun_41M0TXDYD20GGJZVASA0GBCY36
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:43Z · abandoned wrun_41M0TXE3D50GXJMAF18AZW6V4R
cold-start-warmup · suite warmup (tanstack-start) · at 22:16:12Z · abandoned wrun_01M0TXG6HR6PJM96ZTX5PVDH53
cold-start-warmup · suite warmup (python) · at 22:16:17Z · abandoned wrun_01M0TXDBV9GKBACX7VMYQ4C1VV · (+7 more)
run-pickup-stall · promiseAllWorkflow (python) · at 22:16:32Z · abandoned wrun_01M0TXH0ZK7BEXEY27SWJ838CB
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:16:32Z · abandoned wrun_01M0TXH0ZK7BEXEY27SWJ838CA
run-pickup-stall · parallelSleepWorkflow (python) · at 22:16:32Z · abandoned wrun_01M0TXH0ZV0PYJ7Z6XVT814ACV
run-pickup-stall · nullByteWorkflow (python) · at 22:16:32Z · abandoned wrun_01M0TXH0ZX0XFJH14MFVC6RSZY
run-pickup-stall · sleepingWorkflow (python) · at 22:16:32Z · abandoned wrun_01M0TXH0ZSVJ30NH6RPAEY490X
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:17:32Z · abandoned wrun_01M0TXJVKFDMA8H3W102T8C6G7
run-pickup-stall · parallelSleepWorkflow (python) · at 22:17:32Z · abandoned wrun_01M0TXJVKKN8B76FXDTBJDF92S
run-pickup-stall · sleepingWorkflow (python) · at 22:17:32Z · abandoned wrun_01M0TXJVKHZPCAE7T89ZK1A38H
run-pickup-stall · promiseAllWorkflow (python) · at 22:17:32Z · abandoned wrun_01M0TXJVKMENKAEWXSG74MD5DC
run-pickup-stall · nullByteWorkflow (python) · at 22:17:32Z · abandoned wrun_01M0TXJVKS12H4J1VVTXT50Z3V
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:18:04Z · abandoned wrun_41M0TXGP2P0GTMY1S2K9KWS2HP
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:18:04Z · abandoned wrun_41M0TXGV9Q0GTPHT34Y2BQPV2W
run-pickup-stall · instanceMethodStepWorkflow - instance methods with "use step" directive (nuxt) · at 22:18:04Z · abandoned wrun_01M0TXKTVA2VXANES2HKWH2BVT
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:18:32Z · abandoned wrun_01M0TXMP7CP94P4BVQG2HJ6S8K
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:18:32Z · abandoned wrun_01M0TXMP7EVMTKC93ECEX0VYPN
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:18:32Z · abandoned wrun_01M0TXMP7T9GBSVE26X6525R9F
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:19:02Z · abandoned wrun_01M0TXNKKH2HNGEA3NCG0QN5AK
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:19:02Z · abandoned wrun_01M0TXNKKMHKWJ84M5BN85WCVQ
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:19:32Z · abandoned wrun_01M0TXPGTX5SJRMKPG9V3BKZTS

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	685	0	275	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	16921	17	2910	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Skipped
✅ astro-stable-node	134	26
✅ astro-stable-quickjs	134	26
✅ express-stable-node	134	26
✅ express-stable-quickjs	134	26
✅ fastify-stable-node	134	26
✅ fastify-stable-quickjs	134	26
✅ hono-stable-node	134	26
✅ hono-stable-quickjs	134	26
✅ nest-stable-node	134	26
✅ nest-stable-quickjs	134	26
✅ nextjs-turbopack-canary-node	141	19
✅ nextjs-turbopack-canary-quickjs	141	19
✅ nextjs-turbopack-stable-node	160	0
✅ nextjs-turbopack-stable-quickjs	160	0
✅ nextjs-webpack-canary-node	141	19
✅ nextjs-webpack-canary-quickjs	141	19
✅ nextjs-webpack-stable-node	160	0
✅ nextjs-webpack-stable-quickjs	160	0
✅ nitro-stable-node	134	26
✅ nitro-stable-quickjs	134	26
✅ nuxt-stable-node	134	26
✅ nuxt-stable-quickjs	134	26
✅ sveltekit-stable-node	153	7
✅ sveltekit-stable-quickjs	153	7
✅ tanstack-start-node	134	26
✅ tanstack-start-quickjs	134	26
✅ vite-stable-node	134	26
✅ vite-stable-quickjs	134	26

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable-node	134	26
✅ astro-stable-quickjs	134	26
✅ express-stable-node	134	26
✅ express-stable-quickjs	134	26
✅ fastify-stable-node	134	26
✅ fastify-stable-quickjs	134	26
✅ hono-stable-node	134	26
✅ hono-stable-quickjs	134	26
✅ nest-stable-node	134	26
✅ nest-stable-quickjs	134	26
✅ nextjs-turbopack-canary-node	141	19
✅ nextjs-turbopack-canary-quickjs	141	19
✅ nextjs-turbopack-stable-node	160	0
✅ nextjs-turbopack-stable-quickjs	160	0
✅ nextjs-webpack-canary-node	141	19
✅ nextjs-webpack-canary-quickjs	141	19
✅ nextjs-webpack-stable-node	160	0
✅ nextjs-webpack-stable-quickjs	160	0
✅ nitro-stable-node	134	26
✅ nitro-stable-quickjs	134	26
✅ nuxt-stable-node	134	26
✅ nuxt-stable-quickjs	134	26
✅ sveltekit-stable-node	153	7
✅ sveltekit-stable-quickjs	153	7
✅ tanstack-start-node	134	26
✅ tanstack-start-quickjs	134	26
✅ vite-stable-node	134	26
✅ vite-stable-quickjs	134	26

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable-node	134	26
✅ astro-stable-quickjs	134	26
✅ express-stable-node	134	26
✅ express-stable-quickjs	134	26
✅ fastify-stable-node	134	26
✅ fastify-stable-quickjs	134	26
✅ hono-stable-node	134	26
✅ hono-stable-quickjs	134	26
✅ nest-stable-node	134	26
✅ nest-stable-quickjs	134	26
✅ nextjs-turbopack-canary-node	141	19
✅ nextjs-turbopack-canary-quickjs	141	19
✅ nextjs-turbopack-stable-node	160	0
✅ nextjs-turbopack-stable-quickjs	160	0
✅ nextjs-webpack-canary-node	141	19
✅ nextjs-webpack-canary-quickjs	141	19
✅ nextjs-webpack-stable-node	160	0
✅ nextjs-webpack-stable-quickjs	160	0
✅ nitro-stable-node	134	26
✅ nitro-stable-quickjs	134	26
✅ nuxt-stable-node	134	26
✅ nuxt-stable-quickjs	134	26
✅ sveltekit-stable-node	153	7
✅ sveltekit-stable-quickjs	153	7
✅ tanstack-start-node	134	26
✅ tanstack-start-quickjs	134	26
✅ vite-stable-node	134	26
✅ vite-stable-quickjs	134	26

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	0
✅ nextjs-turbopack-quickjs	160	0	0

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Skipped
✅ example	132	28
✅ express	132	28
✅ hono	0	160
✅ nextjs-turbopack	157	3
✅ nitro	132	28
✅ vite	132	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Skipped
✅ example	132	28
✅ express	132	28
✅ nextjs-turbopack	157	3
✅ vite	132	28

📋 View full workflow run

github-actions · 2026-08-24T21:01:02Z

📊 Workflow Benchmarks

commit 2802678 · Mon, 24 Aug 2026 22:35:42 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1282 (+29%) 🔻	1394 🔴 (+26%) 🔻	1421 🔴 (+23%) 🔻	1684 🔴 (+34%) 🔻	30
TTFS	stream	321 (-55%) 💚	1366 🔴 (+25%) 🔻	1437 🔴 (+30%) 🔻	1504 🔴 (+17%) 🔻	30
TTFS	hook + stream	634 (-54%) 💚	1630 🔴 (+11%)	1772 🔴 (+18%) 🔻	5755 🔴 (+261%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	609 (-6.3%)	2006 (+17%) 🔻	2139 (+20%) 🔻	2231 (+15%)	10
Fan-out TTLS	Promise.all(100 steps)	2012 (+4.1%)	4085 (+29%) 🔻	4618 (+40%) 🔻	5748 (-32%) 💚	10
STSO	1020 steps (inline)	117 (+11%)	166 (+12%)	187 (+11%)	262 (+20%) 🔻	1019
WO	1020 steps	158529 (+7.4%)	158529 (+7.4%)	158529 (+7.4%)	158529 (+7.4%)	1
CRTT	first chunk (pooled)	103 (+17%) 🔻	148 (+19%) 🔻	259 (+34%) 🔻	454 (-27%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	145 (+28%)	155 (+19%)	328 (+55%)	4211 (+453%)	117 (-18%)	10
size sweep (100/s, 160B-12KB)	128 (+14%)	157 (+11%)	213 (+14%)	434 (-61%)	144 (+5%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	123 (±0%)	130 (-80%)	156 (-95%)	466 (-90%)	345 (+59%)	3
replay eve-gpt-5.6-sol-2000t (1x)	118 (±0%)	132 (-1%)	169 (±0%)	474 (+37%)	423 (+62%)	2
replay eve-gpt-5.6-sol-2000t (2x)	259 (+111%)	341 (+86%)	566 (+115%)	4078 (+640%)	382 (+68%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 147417ms → this run 158128ms (Δ +10711ms, +7%)

100-150 ms  ████████████████┃███████  main 785  this 569  -216
150-200 ms  ███████░░░░┃              main 216  this 387  +171
200-250 ms  █┃                        main  14  this  50   +36
250-300 ms  ┃                         main   4  this   8    +4
300-350 ms  ┃                         main   0  this   2    +2
400-450 ms  ┃                         main   0  this   2    +2
450-500 ms  ┃                         main   0  this   1    +1

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant  RTT 1ms→5s+             avg         p50          p90           p99     n
control  ······▃█▁▁·▁·  186.7 (+56%)  120 (+13%)   328 (+55%)  4211 (+453%)  3000
sweep    ······▃█▁····     129 (+4%)   117 (+6%)   213 (+14%)    434 (-61%)  3000
gw 1x    ·····▁▆█▁▁···  116.6 (-65%)   107 (+6%)   156 (-95%)    466 (-90%)  5295
eve 1x   ·····▁▆█▁▁···   117.1 (+6%)  105 (+15%)    169 (±0%)    474 (+37%)  5186
eve 2x   ·····▁▃█▄▁·▁·  251.5 (+80%)  154 (+19%)  566 (+115%)  4078 (+640%)  7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control  ▁▁▁▁▁▁▂▁▄█  122–507ms
sweep    █▄▂▂▅▆▁▂▂▂  115–159ms
gw 1x    █▅▂▆▁▂▂▂▄▅  102–140ms
eve 1x   ▃▁█▃▂▄▇▅▄▂  98–145ms
eve 2x   ▂▁▁▁▁▁▁▂▁█  161–802ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep  ▁▂██▅▄▄  128–130ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control  ▁▁▁▁▂▂▂▁█▁  34–102ms
sweep    ▁▆▆▄█▇▁▃▃▂  43–61ms
gw 1x    ▅█▂▁▄▄▄▄▆█  30–37ms
eve 1x   ▃▁▆▃▂▅█▄▇▂  19–28ms
eve 2x   ▅▃▁▃▂▂▁▂▁█  23–54ms

📜 Previous results (1)

`e489c32`

Mon, 24 Aug 2026 21:28:27 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	246 (-75%) 💚	1377 🔴 (+24%) 🔻	1445 🔴 (+25%) 🔻	1572 🔴 (+25%) 🔻	30
TTFS	stream	263 (-63%) 💚	1349 🔴 (+23%) 🔻	1422 🔴 (+28%) 🔻	1461 🔴 (+14%)	30
TTFS	hook + stream	406 (-70%) 💚	1613 🔴 (+9.8%)	1713 🔴 (+14%)	1981 🔴 (+24%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	680 (+4.6%)	1916 (+12%)	4807 (+169%) 🔻	5577 (+187%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2290 (+19%) 🔻	5205 (+64%) 🔻	6646 (+102%) 🔻	8687 (+2.5%)	10
STSO	1020 steps (inline)	70 (-33%) 💚	141 (-4.7%)	161 (-4.2%)	243 (+11%)	1019
WO	1020 steps	140847 (-4.6%)	140847 (-4.6%)	140847 (-4.6%)	140847 (-4.6%)	1
CRTT	first chunk (pooled)	102 (+16%) 🔻	162 (+31%) 🔻	210 (+8.8%)	314 (-49%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	122 (+8%)	195 (+50%)	492 (+132%)	1456 (+91%)	128 (-10%)	10
size sweep (100/s, 160B-12KB)	127 (+12%)	198 (+39%)	445 (+138%)	841 (-25%)	186 (+36%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	210 (+71%)	132 (-80%)	179 (-95%)	309 (-93%)	230 (+6%)	3
replay eve-gpt-5.6-sol-2000t (1x)	118 (±0%)	151 (+13%)	244 (+44%)	1064 (+208%)	806 (+208%)	2
replay eve-gpt-5.6-sol-2000t (2x)	162 (+32%)	215 (+17%)	332 (+26%)	723 (+31%)	354 (+55%)	3

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000t eaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t 6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

github-actions · 2026-08-24T21:03:42Z

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay
✅ `smoke-no-steps`	completed	3	0ms	ok
✅ `smoke-one-step`	completed	6	0ms	ok
✅ `hook-at-step-started`	completed	12	0ms	ok
✅ `hook-at-step-completed`	completed	12	0ms	ok
✅ `hook-at-hook-created`	completed	12	0ms	ok
✅ `deadline-hook-wins`	completed	7	1.0h	ok
✅ `deadline-expires`	completed	7	1.0h	ok
✅ `long-sleep`	completed	11	30.0d	ok
✅ `hook-never-arrives`	stalled	3	0ms	skipped
✅ `step-retries-twice`	completed	10	2.0s	ok
✅ `parallel-steps`	completed	9	0ms	ok
✅ `hook-on-execution-state`	completed	12	0ms	ok
✅ `peek-hook-before-branch`	completed	12	0ms	ok
✅ `peek-hook-after-branch`	completed	12	0ms	ok
✅ `peek-hook-at-registration`	completed	12	0ms	ok
✅ `race-hook-before-probe`	completed	12	0ms	ok
✅ `race-hook-after-probe`	completed	12	0ms	ok
✅ `race-duplicate-delivery`	completed	13	0ms	ok
✅ `attr-hook-before-step`	completed	11	0ms	ok
✅ `attr-hook-after-step`	completed	11	0ms	ok
✅ `attr-from-step-body`	completed	13	0ms	ok
✅ `fork-hook-after-timeout`	completed	14	1.0m	ok
✅ `fork-hook-before-timeout`	completed	14	1.0m	ok
✅ `count-hook-after-timeout`	completed	17	1.0m	ok
✅ `count-hook-before-timeout`	completed	20	1.0m	ok
✅ `stale-read-step-count-fork`	completed	20	1.0m	ok
✅ `stale-read-equal-step-counts`	completed	14	1.0m	ok
✅ `step-vs-step-fork`	completed	12	0ms	ok
✅ `step-vs-step-fork-fenced`	completed	12	0ms	ok
✅ `fence-catches-benign-direction`	completed	12	5ms	ok
✅ `in-flight-before-decision`	completed	17	1.0m	ok
❌ `in-flight-before-decision-counted`	completed	17	1.0m	ok
✅ `in-flight-after-decision`	completed	19	2.0m	ok
✅ `stale-read-step-count-fork-fenced`	completed	20	1.0m	ok
✅ `fork-hook-wins`	completed	13	1.0m	ok
✅ `fork-timeout-wins`	completed	13	1.0m	ok
✅ `unclaimed-payload-under-fork`	completed	17	1.0m	ok
✅ `claimed-payload-under-fork`	completed	17	1.0m	ok
✅ `writers-independent-step-bodies`	completed	12	0ms	ok
✅ `writers-scripted-tempo`	completed	12	0ms	ok
✅ `cancel-mid-step`	cancelled	7	0ms	skipped

Full trace: world-sim.txt

Signed-off-by: Alex Langenfeld <alex.langenfeld@vercel.com>

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feat(streams): add WebSocket capability gate

2802678

Signed-off-by: Alex Langenfeld <alex.langenfeld@vercel.com>

alangenfeld force-pushed the alangenfeld/ws-stream-capability-gate branch from e489c32 to 2802678 Compare August 24, 2026 22:08

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feat(streams): add WebSocket capability gate - #3764

feat(streams): add WebSocket capability gate#3764
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🧪 E2E Test Results

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

🌐 Cross-language Conformance (9 failed)

⚠️ Flaky E2E Tests (passed on retry)

🛠 Infra Events (absorbed by the harness)

E2E Test Summary

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📊 Workflow Benchmarks

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