[world-vercel] Default the events transport to WebSockets by VaguelySerious · Pull Request #4589 · vercel/workflow

VaguelySerious · 2026-10-02T18:11:26Z

Summary

Flips WORKFLOW_EVENTS_TRANSPORT back to ws by default. This reverses #4488, rebased on the per-workflow override from #4566.

isWsEventsTransportEnabled() is true unless the value is http (trimmed, case-insensitive). Unset, empty, or unrecognized values use the WebSocket.
WORKFLOW_EVENTS_TRANSPORT_WS_OVERRIDE_WORKFLOWS keeps working, but now only matters on a deployment pinned to http. Its docs, JSDoc, and tests now say so, and the override tests set http explicitly instead of relying on an unset default.
fix(world-vercel): make the WebSocket events transport opt-in (default WORKFLOW_EVENTS_TRANSPORT to http) #4488 reverted the default because of 1006 closes on messages over the platform's 16 MiB WebSocket limit. fix(world-vercel): split large frames on the WebSocket events transport #4504 fixes that client-side by splitting large frames, and it shipped in 5.0.1.
Docs: worlds.mdx, worlds/v5/vercel.mdx, runtime-tuning.mdx, whats-new.mdx, upgrading-to-v5.mdx, and the package README describe WS as the default and http as the opt-out.
CI: e2e-vercel-prod runs on WS again. e2e-vercel-http-transport still pins http, and e2e-vercel-ws-transport still runs strict mode. Only comments changed.

Known gap, unchanged by this PR (ws-transport.ts, WsEventsTransport.open): the HTTP fallback only kicks in when the handshake fails. A channel that connects and then fails every write keeps taking the WS path for that invocation. The queue's redelivery still retries the step, but nothing de-opts the run to HTTP.

Testing

pnpm vitest run in packages/world-vercel (900 passed)
pnpm typecheck in packages/world-vercel

Docs Preview

Page	Link
Vercel World: `WORKFLOW_EVENTS_TRANSPORT`	https://workflow-docs-git-peter-ws-events-transport-default.vercel.sh/worlds/vercel#workflow_events_transport
Vercel World: `WORKFLOW_EVENTS_TRANSPORT_WS_OVERRIDE_WORKFLOWS`	https://workflow-docs-git-peter-ws-events-transport-default.vercel.sh/worlds/vercel#workflow_events_transport_ws_override_workflows
Worlds config: `WORKFLOW_EVENTS_TRANSPORT`	https://workflow-docs-git-peter-ws-events-transport-default.vercel.sh/docs/configuration/worlds#workflow_events_transport
Runtime tuning: `WORKFLOW_NODE_HTTP`	https://workflow-docs-git-peter-ws-events-transport-default.vercel.sh/docs/configuration/runtime-tuning#workflow_node_http
What's new: Also new in 5.0	https://workflow-docs-git-peter-ws-events-transport-default.vercel.sh/docs/whats-new#also-new-in-50
Upgrading Worlds to v5	https://workflow-docs-git-peter-ws-events-transport-default.vercel.sh/worlds/upgrading-to-v5

🤖 Generated with Claude Code

Reverses #4488 on top of the per-workflow override from #4566. Unset, empty, or any value other than `http` (trimmed, case-insensitive) uses the WebSocket events transport. WORKFLOW_EVENTS_TRANSPORT_WS_OVERRIDE_WORKFLOWS now only matters on a deployment pinned to `http`. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

changeset-bot · 2026-10-02T18:11:32Z

🦋 Changeset detected

Latest commit: 2790125

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	Minor
@workflow/cli	Patch
@workflow/core	Minor
@workflow/web	Patch
workflow	Minor
@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 · 2026-10-02T18:11:42Z

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

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
example-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-astro-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-express-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-hono-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-python-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workbench-vite-workflow	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workflow-docs	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workflow-swc-playground	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workflow-tarballs	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC
workflow-web	Ready	Preview, v0	Oct 2, 2026 6:14pm UTC

github-actions · 2026-10-02T18:11:49Z

🧪 E2E Test Results

✅ All tests passed

⚠️ 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.

health check (CLI) - workflow health command reports healthy endpoints (nextjs-webpack · local-dev / local / node / canary)

🛠 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.

run-pickup-stall · runs app-generated source against a registered step (tanstack-start) · at 18:17:07Z · abandoned wrun_01M3YXANRVSBSMQMZRM5NMGEFC
cold-start-warmup · suite warmup (tanstack-start) · at 18:17:10Z · abandoned wrun_01M3YXANS9BJHD85NX0DREPFZC
run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 18:23:22Z · abandoned wrun_01M3YXP4JENWCXMQBQPDNWV4K7
run-pickup-stall · hookGetConflictWorkflow - awaiting hook.getConflict() registers hook without payload (nextjs-webpack) · at 18:23:29Z · abandoned wrun_01M3YXPBGZJSYZCKS1AW1TJDPB
run-pickup-stall · 'hookGetConflictWithPriorStepWorkflow' - hook.getConflict() does not block step execution (nextjs-webpack) · at 18:23:30Z · abandoned wrun_01M3YXPC80F8CNR8F32B2HNPNV
run-pickup-stall · customSerializationWorkflow - custom class serialization with WORKFLOW_SERIALIZE/WORKFLOW_DESERIALIZE (nextjs-webpack) · at 18:24:46Z · abandoned wrun_01M3YXRPGKY9A4898FC67HHJ2M

E2E Test Summary

Summary

	Passed	Skipped	Total
✅ ▲ Vercel Production	3904	875	4779
✅ 💻 Local Development	4582	551	5133
✅ 📦 Local Production	4582	551	5133
✅ 🐘 Local Postgres	4582	551	5133
✅ 🪟 Windows	342	12	354
✅ 🌐 Cross-language Conformance	68	84	152
✅ dynamic-runs	0	0	0
✅ vercel-http-transport	879	183	1062
✅ vercel-multi-region	27	0	27
✅ vercel-ws-transport	595	113	708
Total	19561	2920	22481

Details by Category

✅ ▲ Vercel Production

App	Passed	Skipped
✅ astro-node	142	35
✅ astro-quickjs	142	35
✅ example-node	142	35
✅ example-quickjs	142	35
✅ express-node	142	35
✅ express-quickjs	142	35
✅ fastify-node	142	35
✅ fastify-quickjs	142	35
✅ hono-node	142	35
✅ hono-quickjs	142	35
✅ nest-node	142	35
✅ nest-quickjs	142	35
✅ nextjs-turbopack-node	169	8
✅ nextjs-turbopack-quickjs	169	8
✅ nextjs-webpack-node	169	8
✅ nextjs-webpack-quickjs	169	8
✅ nitro-node	142	35
✅ nitro-quickjs	142	35
✅ nuxt-node	142	35
✅ nuxt-quickjs	142	35
✅ python-node	66	111
✅ sveltekit-node	161	16
✅ sveltekit-quickjs	161	16
✅ tanstack-start-node	142	35
✅ tanstack-start-quickjs	142	35
✅ vite-node	142	35
✅ vite-quickjs	142	35

✅ 💻 Local Development

App	Passed	Skipped
✅ astro-stable-node	148	29
✅ astro-stable-quickjs	148	29
✅ express-stable-node	148	29
✅ express-stable-quickjs	148	29
✅ fastify-stable-node	148	29
✅ fastify-stable-quickjs	148	29
✅ hono-stable-node	148	29
✅ hono-stable-quickjs	148	29
✅ nest-stable-node	148	29
✅ nest-stable-quickjs	148	29
✅ nextjs-turbopack-canary-node	176	1
✅ nextjs-turbopack-canary-quickjs	176	1
✅ nextjs-turbopack-quickjs-snapshot	176	1
✅ nextjs-turbopack-stable-node	176	1
✅ nextjs-turbopack-stable-quickjs	176	1
✅ nextjs-webpack-canary-node	176	1
✅ nextjs-webpack-canary-quickjs	176	1
✅ nextjs-webpack-stable-node	176	1
✅ nextjs-webpack-stable-quickjs	176	1
✅ nitro-stable-node	148	29
✅ nitro-stable-quickjs	148	29
✅ nuxt-stable-node	148	29
✅ nuxt-stable-quickjs	148	29
✅ sveltekit-stable-node	167	10
✅ sveltekit-stable-quickjs	167	10
✅ tanstack-start-node	148	29
✅ tanstack-start-quickjs	148	29
✅ vite-stable-node	148	29
✅ vite-stable-quickjs	148	29

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable-node	148	29
✅ astro-stable-quickjs	148	29
✅ express-stable-node	148	29
✅ express-stable-quickjs	148	29
✅ fastify-stable-node	148	29
✅ fastify-stable-quickjs	148	29
✅ hono-stable-node	148	29
✅ hono-stable-quickjs	148	29
✅ nest-stable-node	148	29
✅ nest-stable-quickjs	148	29
✅ nextjs-turbopack-canary-node	176	1
✅ nextjs-turbopack-canary-quickjs	176	1
✅ nextjs-turbopack-quickjs-snapshot	176	1
✅ nextjs-turbopack-stable-node	176	1
✅ nextjs-turbopack-stable-quickjs	176	1
✅ nextjs-webpack-canary-node	176	1
✅ nextjs-webpack-canary-quickjs	176	1
✅ nextjs-webpack-stable-node	176	1
✅ nextjs-webpack-stable-quickjs	176	1
✅ nitro-stable-node	148	29
✅ nitro-stable-quickjs	148	29
✅ nuxt-stable-node	148	29
✅ nuxt-stable-quickjs	148	29
✅ sveltekit-stable-node	167	10
✅ sveltekit-stable-quickjs	167	10
✅ tanstack-start-node	148	29
✅ tanstack-start-quickjs	148	29
✅ vite-stable-node	148	29
✅ vite-stable-quickjs	148	29

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable-node	148	29
✅ astro-stable-quickjs	148	29
✅ express-stable-node	148	29
✅ express-stable-quickjs	148	29
✅ fastify-stable-node	148	29
✅ fastify-stable-quickjs	148	29
✅ hono-stable-node	148	29
✅ hono-stable-quickjs	148	29
✅ nest-stable-node	148	29
✅ nest-stable-quickjs	148	29
✅ nextjs-turbopack-canary-node	176	1
✅ nextjs-turbopack-canary-quickjs	176	1
✅ nextjs-turbopack-quickjs-snapshot	176	1
✅ nextjs-turbopack-stable-node	176	1
✅ nextjs-turbopack-stable-quickjs	176	1
✅ nextjs-webpack-canary-node	176	1
✅ nextjs-webpack-canary-quickjs	176	1
✅ nextjs-webpack-stable-node	176	1
✅ nextjs-webpack-stable-quickjs	176	1
✅ nitro-stable-node	148	29
✅ nitro-stable-quickjs	148	29
✅ nuxt-stable-node	148	29
✅ nuxt-stable-quickjs	148	29
✅ sveltekit-stable-node	167	10
✅ sveltekit-stable-quickjs	167	10
✅ tanstack-start-node	148	29
✅ tanstack-start-quickjs	148	29
✅ vite-stable-node	148	29
✅ vite-stable-quickjs	148	29

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	171	0	6
✅ nextjs-turbopack-quickjs	171	0	6

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	68	0	84

✅ dynamic-runs

App	Passed	Failed	Skipped
✅ astro-vercel	0	0	0
✅ example-vercel	0	0	0
✅ express-vercel	0	0	0
✅ fastify-vercel	0	0	0
✅ hono-vercel	0	0	0
✅ nest-vercel	0	0	0
✅ nextjs-turbopack-vercel	0	0	0
✅ nextjs-webpack-vercel	0	0	0
✅ nitro-vercel	0	0	0
✅ nuxt-vercel	0	0	0
✅ sveltekit-vercel	0	0	0
✅ tanstack-start-vercel	0	0	0
✅ vite-vercel	0	0	0

✅ vercel-http-transport

App	Passed	Skipped
✅ example	142	35
✅ express	142	35
✅ hono	142	35
✅ nextjs-turbopack	169	8
✅ nitro	142	35
✅ vite	142	35

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Skipped
✅ example	142	35
✅ express	142	35
✅ nextjs-turbopack	169	8
✅ vite	142	35

📋 View full workflow run

github-actions · 2026-10-02T18:11:57Z

📊 Workflow Benchmarks

commit 2790125 · Fri, 02 Oct 2026 18:37:33 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	378 (-74%) 💚	2324 🔴 (+29%) 🔻	2381 🔴 (+30%) 🔻	2665 🔴 (+25%) 🔻	30
TTFS	stream	2176 (+628%) 🔻	2270 🔴 (+31%) 🔻	2288 🔴 (+29%) 🔻	2312 🔴 (+15%) 🔻	30
TTFS	hook + stream	2155 (+239%) 🔻	2552 🔴 (+26%) 🔻	2625 🔴 (+27%) 🔻	2831 🔴 (+35%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	559 (+14%)	907 (+5.3%)	1018 (+5.8%)	2637 (+31%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1686 (-11%)	3234 (-88%) 💚	6233 (-91%) 💚	10674 (-91%) 💚	10
STSO	1020 steps (inline)	96 (-33%) 💚	147 (-31%) 💚	164 (-41%) 💚	214 (-97%) 💚	1019
WO	1020 steps	144730 (-69%) 💚	144730 (-69%) 💚	144730 (-69%) 💚	144730 (-69%) 💚	1
CRTT	first chunk (pooled)	71 (+20%) 🔻	96 (-10%)	154 (-49%) 💚	4293 (+699%) 🔻	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	84 (+5%)	158 (+5%)	211 (-51%)	402 (-48%)	161 (+14%)	10
size sweep (100/s, 160B-12KB)	90 (-31%)	164 (-71%)	212 (-74%)	574 (-52%)	147 (-67%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	95 (+20%)	156 (+14%)	186 (-1%)	283 (-26%)	197 (-49%)	3
replay eve-gpt-5.6-sol-2000t (1x)	83.5 (-58%)	139 (-10%)	173 (-24%)	376 (-72%)	409 (-48%)	2
replay eve-gpt-5.6-sol-2000t (2x)	98 (-8%)	197 (+19%)	387 (+59%)	1874 (+221%)	204 (-37%)	3

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

1020 steps (inline)

Cumulative STSO time: main 471051ms → this run 144410ms (Δ -326641ms, -69%)

     50-100 ms  ┃                         main   0  this   1    +1
    100-150 ms  █░░░░░░░░░░░░░░░░░░░░░░┃  main   2  this 804  +802
    150-200 ms  █████┃██████████████      main 673  this 199  -474
    200-250 ms  ┃█████                    main 202  this  14  -188
    250-300 ms  ┃█                        main  55  this   0   -55
    300-350 ms  ┃                         main  16  this   1   -15
    350-400 ms  ┃                         main  15  this   0   -15
    400-450 ms  ┃                         main   4  this   0    -4
    450-500 ms  ┃                         main   6  this   0    -6
    500-550 ms  ┃                         main   3  this   0    -3
    550-600 ms  ┃                         main   2  this   0    -2
    600-650 ms  ┃                         main   1  this   0    -1
    650-700 ms  ┃                         main   2  this   0    -2
    700-750 ms  ┃                         main   2  this   0    -2
    750-800 ms  ┃                         main   1  this   0    -1
    800-850 ms  ┃                         main   2  this   0    -2
    850-900 ms  ┃                         main   1  this   0    -1
    900-950 ms  ┃                         main   1  this   0    -1
  1000-1050 ms  ┃                         main   2  this   0    -2
  1500-1550 ms  ┃                         main   1  this   0    -1
  1900-1950 ms  ┃                         main   1  this   0    -1
  2150-2200 ms  ┃                         main   1  this   0    -1
  2200-2250 ms  ┃                         main   1  this   0    -1
  2300-2350 ms  ┃                         main   1  this   0    -1
  2650-2700 ms  ┃                         main   1  this   0    -1
  3100-3150 ms  ┃                         main   1  this   0    -1
  3300-3350 ms  ┃                         main   1  this   0    -1
  3750-3800 ms  ┃                         main   2  this   0    -2
  4200-4250 ms  ┃                         main   1  this   0    -1
  4650-4700 ms  ┃                         main   1  this   0    -1
  4900-4950 ms  ┃                         main   1  this   0    -1
  5250-5300 ms  ┃                         main   1  this   0    -1
  5350-5400 ms  ┃                         main   1  this   0    -1
  6750-6800 ms  ┃                         main   1  this   0    -1
  6800-6850 ms  ┃                         main   1  this   0    -1
  6950-7000 ms  ┃                         main   1  this   0    -1
  7650-7700 ms  ┃                         main   1  this   0    -1
  7700-7750 ms  ┃                         main   1  this   0    -1
  8050-8100 ms  ┃                         main   1  this   0    -1
  8300-8350 ms  ┃                         main   1  this   0    -1
11000-11050 ms  ┃                         main   1  this   0    -1
11750-11800 ms  ┃                         main   1  this   0    -1
12850-12900 ms  ┃                         main   1  this   0    -1
13550-13600 ms  ┃                         main   1  this   0    -1
21250-21300 ms  ┃                         main   1  this   0    -1
39850-39900 ms  ┃                         main   1  this   0    -1
52350-52400 ms  ┃                         main   1  this   0    -1

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

variant  RTT 1ms→5s+             avg         p50         p90           p99     n
control  ······▃█▁····   132.7 (+2%)  126 (+22%)  211 (-51%)    402 (-48%)  3000
sweep    ······▃█▁▁···  135.1 (-56%)  118 (-24%)  212 (-74%)    574 (-52%)  3000
gw 1x    ·····▁▄█▁····  123.6 (+10%)  111 (+17%)   186 (-1%)    283 (-26%)  5295
eve 1x   ·····▁▅█▁▁···  120.5 (-22%)   110 (-2%)  173 (-24%)    376 (-72%)  5186
eve 2x   ·····▁▂█▃▁▁▁·  187.5 (+40%)  144 (+23%)  387 (+59%)  1874 (+221%)  7779

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

control  ▁▁▃▁▄▃█▃▇▃  127–143ms
sweep    ▄▅█▅▅▁▃▂▃▂  112–170ms
gw 1x    ▄▅▄▇▁▇█▂▅▄  114–132ms
eve 1x   ▆▃▆▁▂█▅▄▂▃  110–134ms
eve 2x   █▁▁▁▁▂▁▂▂▁  131–482ms

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

sweep  ▃▆▆█▅▂▁  133–137ms

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

control  ▁▁▄▃█▅▃▂█▄  37–46ms
sweep    ▁▄▃▅█▂▃▄▅▂  51–69ms
gw 1x    ▃▇▂▁▃▇█▄▂▃  34–42ms
eve 1x   █▆▆▁▄█▅▅▁▇  20–25ms
eve 2x   ▇▅▃█▇█▅▁▃▇  21–30ms

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 · 2026-10-02T18:15:46Z

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 42 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
✅ `step-vs-timer-early-settlement`	completed	8	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

github-actions · 2026-10-02T18:16:37Z

Framework	Flow route	Step reg.	Framework output
hono	267.2 KiB (±0)	97.3 KiB (±0)	2.01 MiB (+305 B)
nextjs-turbopack	274.6 KiB (±0)	426 B (±0)	986.1 KiB (±0)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

2790125 · run

github-actions · 2026-10-02T18:33:50Z

No backport to stable for 9ca188a (AI decision).

This flips the default value of WORKFLOW_EVENTS_TRANSPORT from http to ws — a behavior change to an existing configuration surface (carrying a minor changeset), not a fix for a defect on the maintenance line. It also depends on code that does not exist on stable: git ls-tree origin/stable shows no packages/world-vercel/src/ws-transport.ts or ws-transport-enabled.ts, so the WebSocket events transport is a main-only feature. The PR itself notes a known unfixed gap (no write-failure de-opt), which is further reason not to push this onto users who stayed behind for stability.

To override, re-run the Backport to stable workflow manually via workflow_dispatch and paste this commit SHA into the ref input:

9ca188a1e9ec229af92bf82f4ead511ca3a626f2

vercel Bot deployed to Preview – workflow-docs October 2, 2026 18:13 View deployment

VaguelySerious marked this pull request as ready for review October 2, 2026 18:15

VaguelySerious requested a review from a team as a code owner October 2, 2026 18:15

shalabhc approved these changes Oct 2, 2026

View reviewed changes

VaguelySerious merged commit 9ca188a into main Oct 2, 2026
184 of 187 checks passed

VaguelySerious deleted the peter/ws-events-transport-default branch October 2, 2026 18:33

This was referenced Oct 2, 2026

Version Packages #4580

Open

Version Packages Thegreatsura/workflow#1

Open

Navigation Menu

[world-vercel] Default the events transport to WebSockets - #4589

[world-vercel] Default the events transport to WebSockets#4589
VaguelySerious merged 1 commit into
mainfrom
peter/ws-events-transport-default

VaguelySerious commented Oct 2, 2026 •

edited

Loading

Uh oh!

changeset-bot Bot commented Oct 2, 2026

Uh oh!

vercel Bot commented Oct 2, 2026 •

edited

Loading

Uh oh!

github-actions Bot commented Oct 2, 2026 •

edited

Loading

Uh oh!

github-actions Bot commented Oct 2, 2026 •

edited

Loading

Uh oh!

github-actions Bot commented Oct 2, 2026

Uh oh!

github-actions Bot commented Oct 2, 2026

Uh oh!

Uh oh!

github-actions Bot commented Oct 2, 2026

Uh oh!

This branch was successfully deployed

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Conversation

VaguelySerious commented Oct 2, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Testing

Docs Preview

Uh oh!

changeset-bot Bot commented Oct 2, 2026

🦋 Changeset detected

Uh oh!

vercel Bot commented Oct 2, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

github-actions Bot commented Oct 2, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🧪 E2E Test Results

⚠️ Flaky E2E Tests (passed on retry)

🛠 Infra Events (absorbed by the harness)

E2E Test Summary

Uh oh!

github-actions Bot commented Oct 2, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

📊 Workflow Benchmarks

Uh oh!

github-actions Bot commented Oct 2, 2026

Sim World

Uh oh!

github-actions Bot commented Oct 2, 2026

Uh oh!

Uh oh!

github-actions Bot commented Oct 2, 2026

Uh oh!

This branch was successfully deployed

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

VaguelySerious commented Oct 2, 2026 •

edited

Loading

vercel Bot commented Oct 2, 2026 •

edited

Loading

github-actions Bot commented Oct 2, 2026 •

edited

Loading

github-actions Bot commented Oct 2, 2026 •

edited

Loading