Chat hangs on last couple of tokens

[ulugbekna]

Type: Bug

repro:

1. turn off websockets support just in case

  "github.copilot.chat.advanced.responsesApi.webSocket.enabled": false,

2. open chat, set it to gpt-5.4 (default reasoning effort)
3. ask something like "how do I solve differential equations? use no reasoning" - stream starts, last couple of tokens are not rendered for many seconds (~20s)

VS Code version: Code - Insiders 1.118.0-insider (Universal) (102df5b, 2026-04-22T11:25:25Z)
OS version: Darwin arm64 25.4.0
Modes:

Prompt Details

Info: [CopilotCLIChatSessionContentProvider] listSessions took 79.34062500018626ms
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: false.
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: true.
Debug: [CopilotCLI] Found 33 JSONL sessions and 0 legacy sessions
Info: [CopilotCLIChatSessionContentProvider] listSessions took 17.285333999898285ms
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: false.
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: true.
Debug: [CopilotCLI] Found 33 JSONL sessions and 0 legacy sessions
Info: [CopilotCLIChatSessionContentProvider] listSessions took 7.914917000103742ms
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: false.
Trace: [GitServiceImpl][doOpenRepository] Active repository: {"_repo":{"rootUri":{"$mid":1,"fsPath":"/Users/ulugbekna/code/vscode","external":"file:///Users/ulugbekna/code/vscode","path":"/Users/ulugbekna/code/vscode","scheme":"file"},"inputBox":{},"kind":"repository","state":{},"ui":{},"isUsingVirtualFileSystem":false},"rootUri":{"$mid":1,"fsPath":"/Users/ulugbekna/code/vscode","external":"file:///Users/ulugbekna/code/vscode","path":"/Users/ulugbekna/code/vscode","scheme":"file"},"kind":"repository","isUsingVirtualFileSystem":false,"headBranchName":"main","headCommitHash":"b2ffe3f008b1924cc5de172cefc1fc5bec28d3a8","headIncomingChanges":0,"headOutgoingChanges":0,"upstreamBranchName":"main","upstreamRemote":"origin","isRebasing":true,"remotes":["origin"],"remoteFetchUrls":["https://github.com/microsoft/vscode.git"],"worktrees":[{"name":"vscode","path":"/Users/ulugbekna/code/vscode","ref":"refs/heads/main","detached":false,"main":true},{"name":"agents-autopilot-dialog-dont-show-again","path":"/Users/ulugbekna/code/vscode.worktrees/agents-autopilot-dialog-dont-show-again","ref":"refs/heads/ulugbekna/agents/autopilot-dialog-dont-show-again","detached":false,"main":false},{"name":"agents-enable-disable-skills-agent-ui","path":"/Users/ulugbekna/code/vscode.worktrees/agents-enable-disable-skills-agent-ui","ref":"refs/heads/ulugbekna/agents/enable-disable-skills-agent-ui","detached":false,"main":false},{"name":"copilot-close-viper","path":"/Users/ulugbekna/code/vscode.worktrees/copilot-close-viper","ref":"refs/heads/ulugbekna/copilot/close-viper","detached":false,"main":false}],"changes":{"mergeChanges":[],"indexChanges":[],"workingTree":[],"untrackedChanges":[]},"_onDidChangeSignal":{"_observers":{},"debugName":"Observable Signal From Event"},"headBranchNameObs":{"_observers":{},"_debugNameData":{},"_state":0,"_updateCount":0,"_dependencies":{},"_dependenciesToBeRemoved":{},"_isUpdating":false,"_isComputing":false,"_didReportChange":false,"_isInBeforeUpdate":false,"_isReaderValid":false,"_removedObserverToCallEndUpdateOn":null},"headCommitHashObs":{"_observers":{},"_debugNameData":{},"_state":0,"_updateCount":0,"_dependencies":{},"_dependenciesToBeRemoved":{},"_isUpdating":false,"_isComputing":false,"_didReportChange":false,"_isInBeforeUpdate":false,"_isReaderValid":false,"_removedObserverToCallEndUpdateOn":null},"upstreamBranchNameObs":{"_observers":{},"_debugNameData":{},"_state":0,"_updateCount":0,"_dependencies":{},"_dependenciesToBeRemoved":{},"_isUpdating":false,"_isComputing":false,"_didReportChange":false,"_isInBeforeUpdate":false,"_isReaderValid":false,"_removedObserverToCallEndUpdateOn":null},"upstreamRemoteObs":{"_observers":{},"_debugNameData":{},"_state":0,"_updateCount":0,"_dependencies":{},"_dependenciesToBeRemoved":{},"_isUpdating":false,"_isComputing":false,"_didReportChange":false,"_isInBeforeUpdate":false,"_isReaderValid":false,"_removedObserverToCallEndUpdateOn":null},"isRebasingObs":{"_observers":{},"_debugNameData":{},"_state":0,"_updateCount":0,"_dependencies":{},"_dependenciesToBeRemoved":{},"_isUpdating":false,"_isComputing":false,"_didReportChange":false,"_isInBeforeUpdate":false,"_isReaderValid":false,"_removedObserverToCallEndUpdateOn":null},"_checkIsIgnored":{"_waitingTimeMs":1000,"_queue":[],"_timeout":null},"_isIgnored":{"_map":{},"_map2":{}}}
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: true.
Debug: [CopilotCLI] Found 33 JSONL sessions and 0 legacy sessions
Info: [CopilotCLIChatSessionContentProvider] listSessions took 11.174499999731779ms
Trace: RemoteEmbeddingsComputer::computeEmbeddings started
Trace: RemoteEmbeddingsComputer::computeEmbeddings success. Elapsed 257.9326670002192
Debug: Related Information: Remote similarly request took 258ms
Debug: Related Information: Successfully Calculated, returning 258ms
Trace: RemoteEmbeddingsComputer::computeEmbeddings started
Trace: RemoteEmbeddingsComputer::computeEmbeddings success. Elapsed 168.7464589998126
Debug: Related Information: Remote similarly request took 169ms
Debug: Related Information: Successfully Calculated, returning 169ms
Trace: [CopilotCLI] [DIFF] getActiveDiffByTab: tab is not a diff tab
Trace: [CopilotCLI] [DIFF] getActiveDiffByTab: tab is not a diff tab
Trace: [GitServiceImpl][getRepositoryFetchUrls] URI: newissue:/NewIssue.md?%7B%22origin%22%3A%22repo%3Amicrosoft%2Fvscode%3F%257B%2522folderManagerRootUri%2522%253A%2522file%253A%252F%252F%252FUsers%252Fulugbekna%252Fcode%252Fvscode%2522%257D%22%7D
Trace: [GitServiceImpl][getRepositoryFetchUrls] No repository root found
Trace: RemoteEmbeddingsComputer::computeEmbeddings started
Trace: RemoteEmbeddingsComputer::computeEmbeddings success. Elapsed 247.06125000026077
Debug: Related Information: Remote similarly request took 247ms
Debug: Related Information: Successfully Calculated, returning 247ms
Trace: RemoteEmbeddingsComputer::computeEmbeddings started
Trace: RemoteEmbeddingsComputer::computeEmbeddings success. Elapsed 164.10791700007394
Debug: Related Information: Remote similarly request took 164ms
Debug: Related Information: Successfully Calculated, returning 164ms
Trace: RemoteEmbeddingsComputer::computeEmbeddings started
Trace: RemoteEmbeddingsComputer::computeEmbeddings success. Elapsed 254.6163749997504
Debug: Related Information: Remote similarly request took 255ms
Debug: Related Information: Successfully Calculated, returning 255ms
Trace: RemoteEmbeddingsComputer::computeEmbeddings started
Trace: RemoteEmbeddingsComputer::computeEmbeddings success. Elapsed 329.0872499998659
Debug: Related Information: Remote similarly request took 330ms
Debug: Related Information: Successfully Calculated, returning 330ms
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: false.
Debug: [context keys] Window state change. Needs offline check: false, active: true, focused: true.
Debug: [CopilotCLI] Found 33 JSONL sessions and 0 legacy sessions
Info: [CopilotCLIChatSessionContentProvider] listSessions took 12.653249999973923ms
Trace: RemoteEmbeddingsComputer::computeEmbeddings started
Trace: RemoteEmbeddingsComputer::computeEmbeddings success. Elapsed 236.0215409998782
Debug: Related Information: Remote similarly request took 237ms
Debug: Related Information: Successfully Calculated, returning 237ms

Request IDs

cbf96f2b-9c91-4de7-b158-665251d2382e
f275a27f-85a7-47ec-919d-d7bb1d8b6122
c0d612b8-8196-4c90-91c7-5d71c241cd19
2095a558-ddce-4bc6-a864-a295f6284b86
29526330-8226-4393-afe6-eba7a932e251
97a9fbf7-f7de-45a3-a986-a4b423598afe
08f63962-e1df-49e0-809c-79f32cd53668
51c57eeb-5c55-4784-81c4-2d91212af1bd

System Info

Item	Value
CPUs	Apple M4 Pro (14 x 2400)
GPU Status	2d_canvas: enabled GPU0: VENDOR= 0x106b [Google Inc. (Apple)], DEVICE=0x0000 [ANGLE (Apple, ANGLE Metal Renderer: Apple M4 Pro, Version 26.4.1 (Build 25E253))], DRIVER_VENDOR=Apple, DRIVER_VERSION=26.4.1 ACTIVE Machine model name: Mac Machine model version: 16.8 direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: enabled_on trees_in_viz: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	5, 5, 6
Memory (System)	48.00GB (0.16GB free)
Process Argv	--log info --log github.copilot-chat=trace --log github.vscode-pull-request-github=debug --crash-reporter-id 8c80ab9c-ee3f-4087-8f5f-a4efe42eaf63
Screen Reader	no
VM	0%

Extensions (70)

Extension	Author (truncated)	Version
Bookmarks	ale	14.1.1
tsl-problem-matcher	amo	0.6.2
markdown-mermaid	bie	1.32.0
cerebras-chat	Cer	0.1.20
npm-intellisense	chr	1.4.5
esbuild-problem-matchers	con	0.0.3
vscode-eslint	dba	3.0.24
gitlens	eam	2026.4.220537
EditorConfig	Edi	0.18.2
prettier-vscode	esb	12.4.0
codespaces	Git	1.18.13
remotehub	Git	0.65.2026031901
vscode-pull-request-github	Git	0.139.2026042215
go	gol	0.52.2
gc-excelviewer	Gra	4.2.65
hediet-power-tools	hed	0.4.0
vscode-drawio	hed	1.9.250226013
lldb-dap	llv	0.4.1
rainbow-csv	mec	3.24.1
template-string-converter	meg	0.6.1
vscode-azureresourcegroups	ms-	0.12.4
vscode-containers	ms-	2.4.1
vscode-docker	ms-	2.0.0
debugpy	ms-	2026.3.2026032701
python	ms-	2026.5.2026032701
vscode-pylance	ms-	2026.2.100
vscode-python-envs	ms-	1.29.2026041601
jupyter	ms-	2025.10.2026042201
jupyter-keymap	ms-	1.1.2
jupyter-renderers	ms-	1.3.2025062701
vscode-jupyter-cell-tags	ms-	0.1.9
vscode-jupyter-slideshow	ms-	0.1.6
remote-ssh	ms-	0.123.2026033115
remote-ssh-edit	ms-	0.87.0
remote-wsl	ms-	0.104.3
azure-repos	ms-	0.41.2026031901
cpptools	ms-	1.31.5
hexeditor	ms-	1.11.1
kusto-client	ms-	0.3.2026041703
remote-explorer	ms-	0.6.2026031809
remote-repositories	ms-	0.43.2026031901
remote-server	ms-	1.6.2026041509
test-adapter-converter	ms-	0.2.1
ts-file-path-support	ms-	1.0.0
vscode-diagnostic-tools	ms-	1.2.0
vscode-github-issue-notebooks	ms-	0.0.134
vscode-js-profile-flame	ms-	1.0.9
vscode-speech	ms-	0.16.0
wasm-dwarf-debugging	ms-	1.0.1
web-editors	ms-	0.3.0
ocaml-platform	oca	2.0.1
chatgpt	ope	26.5417.40842
refactor	p42	3.0.1
material-product-icons	PKi	1.7.1
excalidraw-editor	pom	3.9.1
deoptexplorer-vscode	rbu	1.1.2
toggle	reb	0.0.2
vscode-xml	red	0.29.2025112508
vscode-yaml	red	1.22.0
LiveServer	rit	5.7.10
svg-preview	Sim	2.8.3
graphviz-interactive-preview	tin	0.3.5
tldraw-vscode	tld	2.247.0
ulugbek-s-power-tools	ulu	0.0.2
errorlens	use	3.28.0
explorer	vit	1.50.2
vim	vsc	1.32.4
vscode-alternate-file	wil	0.3.1
pretty-ts-errors	Yoa	0.8.7
vscode-selfhost-test-provider	ms-	0.4.0

A/B Experiments

vsliv368cf:30146710
pythonvspyt551:31249597
nativeloc1:31118317
dwcopilot:31158714
471b6256:31240254
dwoutputs:31242946
copilot_t_ci:31333650
g012b348:31231168
pythonrdcb7:31268811
pythonpcpt1:31399616
6518g693:31302842
6abeh943:31336334
envsactivate1:31349248
editstats-enabled:31346256
cloudbuttont:31366566
3efgi100_wstrepl:31403338
55ia6109:31457054
use-responses-api:31390341
je187915:31401257
cp_cls_t_966_ss:31454198
inlinechat_v2_hd992725:31445440
c0683394:31481635
8hhj4413:31478653
ge8j1254_inline_auto_hint_haiku:31490507
38bie571_auto:31487346
cp_cls_c_1081:31454833
conptydll_true:31485575
ia-use-proxy-models-svc:31446143
e9c30283:31453065
test_treatment2:31471001
46204921:31447328
idci7584:31454084
nes_chat_context_disabled:31451402
e3e4d672:31454087
ei9d7968:31462942
534a6447:31478742
hg17d649:31455236
nes-extended-on:31455475
nes-vscode-team-custom:31472622
vscode-team-custom-2:31480564
jc933416:31462667
89g7j272:31480197
7e884298:31462391
4f032803_compaction:31499499
7e187181:31482583
cpptoolsoff-v2:31475362
i2gc6536:31472020
1g3cj959:31494704
h08i8180_copy:31475366
23c7c724:31491644
client_tst_t:31486874
po_split_t:31488387
ddid_t:31478204
getcmakediagnosticsoff:31489825
ja75b849:31492254
bjc72774_agent_sandbox:31488286
7df3h592:31491241
pro_large_t:31499377
606h2495_c:31485219
cp_cls_c_1082:31491634
719di409_sum_t:31499469
0he74425_c:31494278
nes-cj-aftline:31490296
cc5hd740:31492954
logging_enabled_new:31490725
nes-ew-div-cursorline:31494905

[ulugbekna]

Dumping the stream using this PR, I see that somehow the event response.output_item.done' that we wait for comes 12 seconds after the message stream actually ended with response.output_item.done' event.

2026-04-22T17:24:21.501Z response.output_text.delta
{
  "content_index": 0,
  "delta": " types",
  "item_id": "CeYNZ+2q1uHwwSfEi+XacqkUaHrdVF2WmpmoM0qqwfjSAbbNFI9lHRVUT8owUMq9kKHgaxW4/AEgv8xdw+7TmkJMDJ6xEzH15LoHNijVAKxy3cwcZepMehiGUHrcY0mBl20A81iL5Kbm92kneuQkBQlxQMt/jaUhp8USO4A1J6JgGEBnDzrAT53WTwyBW9B8CF83Kdox74iEtqVAle5tGdtoavMOtg5adxaDqZIMq2xMVZnHjGjSJ8i84tTks9r4ELejJoteYlRecHZyaY/Mg7Bb8p4wQVsBa3jaFD+87s5IK9VVm7eL0l0jQxqN8p9bhKhy0d47IHuvUarobp7/muXHRKtbnCYjH9vLqE5eA1fHslqegAP8IKGG8qGaME+r416lKECa5mpjy43jkkskuDE=",
  "logprobs": [],
  "obfuscation": "z3Tstnu3ze",
  "output_index": 1,
  "sequence_number": 295,
  "type": "response.output_text.delta"
}

2026-04-22T17:24:21.503Z response.output_text.delta
{
  "content_index": 0,
  "delta": ".",
  "item_id": "+v8AK5Me0e8xolxTdUvue+BH0PnrjAr7aEjIORWVgR7swrud0AXGb4WymSuqiXip9kkVhVaWpV4nciqkNH4sdyRQDlygv77dTuyS7tWFStJRSYjAgk7epxgeppx/1Q620gAHvf2IykJ8OU680USLeMs4XsCRu0WBf1Z2C1IvyK1EyeakLuQgj2C5Bu5cSL8TUQOJvglG/USGmllR+DjT/KVVi1Ltqzc2rIEetcygNe6MPYefANBXeMLBD6Z1N9/tW0eWGp3r2jKmRpZm2I1GG9ApH9epDM6yYtJe+nmtRJLHu65QD31Qqx4c/gVg6Y8cbKzL93nLxnZNGsTZfhKqCmhXiXBd9/B7lk1mT+InWajen/6ivIA6JUd+LTRkfoctKQ6bFSCq/e5PUE96kepEP9Q=",
  "logprobs": [],
  "obfuscation": "gYmz23ZlfCl9UXD",
  "output_index": 1,
  "sequence_number": 296,
  "type": "response.output_text.delta"
}

2026-04-22T17:24:21.505Z response.output_text.done
{
  "content_index": 0,
  "item_id": "Y07Xfo0nh7E1Rq/kGD7e2jw7Uj9e2Q989wfFwaCZmoqtA7A1o6UHTIaQDdhWFYiRGW45Ezqzmk6wSd5/vYSgLJaHb9p4YzjGE+ciwt7mBBXXuoAkxZaMJt3+JCqLlK+hdR7zQ+28dS0clsqzfoNdCBFIJK+hkmRmCphEnkOP3p8IjAHyRDUqhS3WU4WNDuz5A7yx0Iw9/yH72DvxCxNaE2cOmGJkH9ubDzNAfY5vxjcgFr1vuPoDlqZxgvqbm/SxymnBed3LIA9g3lrh3tT5x1FEFdUmuGaLRErbEHzH9k2ZsbgdQfGQI9Nu6F8+03jzAhD+5OaZNlYB7PsrbU1TfQk+aZEIf/YTDiPRIdZXor/UPw+44Da7Ee8lV6AGlv24nnQiLH0Q5FhqQHx/aT7GH6o=",
  "logprobs": [],
  "output_index": 1,
  "sequence_number": 297,
  "text": "Solve a differential equation by identifying its type and applying the matching method.\n\nCommon workflow:\n1. Put it in a standard form.\n2. Classify it: ordinary or partial, first-order or higher-order, linear or nonlinear, separable, exact, etc.\n3. Choose a method that fits the class.\n4. Integrate or transform the equation.\n5. Apply initial or boundary conditions to find constants.\n6. Check the result by substituting it back into the original equation.\n\nCommon methods:\n- Separable equations: separate variables, then integrate.\n- Linear first-order equations: use an integrating factor.\n- Exact equations: verify exactness, then find a potential function.\n- Homogeneous or substitution-based equations: use a change of variables.\n- Higher-order linear equations with constant coefficients: solve the characteristic equation.\n- Nonhomogeneous linear equations: use undetermined coefficients or variation of parameters.\n- Systems of equations: use elimination, eigenvalues/eigenvectors, or matrix methods.\n- PDEs: use separation of variables, transforms, or characteristics, depending on the equation.\n\nExample:\nFor\n$$\n\\frac{dy}{dx} = ky\n$$\nthe general solution is\n$$\ny = Ce^{kx}.\n$$\n\nIf you want, I can give a very short “cheat sheet” for the main equation types.",
  "type": "response.output_text.done"
}

2026-04-22T17:24:33.250Z response.content_part.done
{
  "content_index": 0,
  "item_id": "Wo7wKCIX3Na4PbwIdardtj4rxRp4GudZHuH523532IhPBGjZKTgO6FggUk+8qkrOxDlSbHlTuQ5SurFq7Nki99ZhTRPOJYL5niz952pKbyFDujDd7gOZ5yzmKSy61kt13LF66MXulgMqjbu5cLchLC3IhfLesazMHva1ZHW7b63SCaUY248Go/Kpe/XtLRMKKtX4YufXO/9kIkjCyWS7EQ9+yq/lZ4mSDlxj9k/PJRjmP+2euvv3oZACYnDPcvR2hrGfYPl7t6gG3zq0Q/KUq/CGEvEosJboQtcvEkiqPA2785f7ZS3rL/S5A4QEfS3eUaXyNGlunkpxKL+hjZK0bbmmbIRsdQeXa/KivdvlbvM1cFAlorP7pRF5jwIRYoKmPjRWJdoVcFe6RkYz1FdJjIc=",
  "output_index": 1,
  "part": {
    "annotations": [],
    "logprobs": [],
    "text": "Solve a differential equation by identifying its type and applying the matching method.\n\nCommon workflow:\n1. Put it in a standard form.\n2. Classify it: ordinary or partial, first-order or higher-order, linear or nonlinear, separable, exact, etc.\n3. Choose a method that fits the class.\n4. Integrate or transform the equation.\n5. Apply initial or boundary conditions to find constants.\n6. Check the result by substituting it back into the original equation.\n\nCommon methods:\n- Separable equations: separate variables, then integrate.\n- Linear first-order equations: use an integrating factor.\n- Exact equations: verify exactness, then find a potential function.\n- Homogeneous or substitution-based equations: use a change of variables.\n- Higher-order linear equations with constant coefficients: solve the characteristic equation.\n- Nonhomogeneous linear equations: use undetermined coefficients or variation of parameters.\n- Systems of equations: use elimination, eigenvalues/eigenvectors, or matrix methods.\n- PDEs: use separation of variables, transforms, or characteristics, depending on the equation.\n\nExample:\nFor\n$$\n\\frac{dy}{dx} = ky\n$$\nthe general solution is\n$$\ny = Ce^{kx}.\n$$\n\nIf you want, I can give a very short “cheat sheet” for the main equation types.",
    "type": "output_text"
  },
  "sequence_number": 298,
  "type": "response.content_part.done"
}

2026-04-22T17:24:33.263Z response.output_item.done
{
  "item": {
    "content": [
      {
        "annotations": [],
        "logprobs": [],
        "text": "Solve a differential equation by identifying its type and applying the matching method.\n\nCommon workflow:\n1. Put it in a standard form.\n2. Classify it: ordinary or partial, first-order or higher-order, linear or nonlinear, separable, exact, etc.\n3. Choose a method that fits the class.\n4. Integrate or transform the equation.\n5. Apply initial or boundary conditions to find constants.\n6. Check the result by substituting it back into the original equation.\n\nCommon methods:\n- Separable equations: separate variables, then integrate.\n- Linear first-order equations: use an integrating factor.\n- Exact equations: verify exactness, then find a potential function.\n- Homogeneous or substitution-based equations: use a change of variables.\n- Higher-order linear equations with constant coefficients: solve the characteristic equation.\n- Nonhomogeneous linear equations: use undetermined coefficients or variation of parameters.\n- Systems of equations: use elimination, eigenvalues/eigenvectors, or matrix methods.\n- PDEs: use separation of variables, transforms, or characteristics, depending on the equation.\n\nExample:\nFor\n$$\n\\frac{dy}{dx} = ky\n$$\nthe general solution is\n$$\ny = Ce^{kx}.\n$$\n\nIf you want, I can give a very short “cheat sheet” for the main equation types.",
        "type": "output_text"
      }
    ],
    "id": "1qWVcif/aFlc31jZLn6c/EEkdP6WMT78oqVwMQ7bzhpU1lAfDDtw2V6Y5F+1q5IO+3qySYKMkYXCzcyQuKcOcAkGymZ71UPDUAnrrYGqSU+/l2qX7f8m13PDh4Rld54bUMyYvXEAlwp8lPdtVlFm+J8/4noBMPDiidE+Ttp/Pbsod2q4zzvYvNcmzpo6D16jM04lXkTjLV6Eo51j/MgxpyWUSKGHCGiKtztiF0wSeaNcs3PmgDusQpFm79ibg/M9jKN6TSWJiUaMA7MMRg9u8KQDYF4Le7dSZsH5qf3qMfSCNtE5GTD6hhrVGKD2TNPYN88I79OGAH2ba9FxINx1Dj+ff5A87608t2zCIJyi5lZEJ+xay8pF+D/5KNYjFmnp3SOfx4ztJwNwh8G9nJuLIZY=",
    "phase": "final_answer",
    "role": "assistant",
    "status": "completed",
    "type": "message"
  },
  "output_index": 1,
  "sequence_number": 299,
  "type": "response.output_item.done"
}

2026-04-22T17:24:33.273Z response.completed
{
  "response": {
    "background": false,
    "completed_at": 1776878661,
    "created_at": 1776878656,
    "error": null,
    "frequency_penalty": 0,
    "id": "1jHmVTqHmUKL4l4KnMO/3rRwRVeYnrZN3PniHLYBRaqRqDJt/SZyJddHNLLz4AKjudDaY6otMHk7t6fwTY53UfpgAJf9Z+aH+qyJZUNT/21WB6VG2pargVuo4YNcEQD9ZV3btIKbNiq5+AR1OuhZ/bJGNl3RV2kNpQPY98ggseKFJH9vYC+vtCQr/j9tclg5yPbJiUAi6TBFM1M+2ud1/p+6mZixjNs0N7bs0sBjbnTlY7Ub5QS/RglWpjEgraudJ6UgEcina51kQ2BmIOcsGnu8xy4PsEhJyIBnhJplqWe2AL8I854noPTH3jDUAujffqsQiPnyNeq83WE+tidQUvEhPT26As0LkOd4oKhBi6cz7UpSl/WHsJYyr8zM2ctCP/VAUZTjZWTHobd2CUIQUsq6",
    "incomplete_details": null,
    "instructions": null,
    "max_output_tokens": 128000,
    "max_tool_calls": null,
    "metadata": {},
    "model": "gpt-5.4-2026-03-05",
    "moderation": null,
    "object": "response",
    "output": [
      {
        "content": [
          {
            "annotations": [],
            "logprobs": [],
            "text": "I’ll answer directly and keep it high-level, without step-by-step reasoning.",
            "type": "output_text"
          }
        ],
        "id": "sFxx6CT4st7h5IOFrkitH7aVqDZNUwYLp5BTHjxOwQ35nZqqHWEoeZCJB48HKel3ztOKu6kmDXQOh2w5PqMJ8k0gemH775EKRGhWGLdtwJ/R/KNvFTtkOtOfR+ZvsoIAkDVpVlb3mIyJlt/2xebUomoq+Re9m2dtcbUpn4a+O6rOqld9l1vs0emNYhqD6J05k/XEnfFwXIRftcF7iuJ3Ld2yH/TZKYLacDSTSYet/BXSGxvidHCXFhNKuS0VD8yEvEhVfgCku0xh+itT4vUO2cjI3TZ+CJRppXoX/vymc7ReysdNYuzk8TOFxFbyiiM1QvSj6WIz9YVpnCK1E4X0BtVGvFHyqZBKE+5udr5LOJOvogL0H+M5aygXEVfef2h/VpajGsgUYX2h4fwDPww0XkQ=",
        "phase": "commentary",
        "role": "assistant",
        "status": "completed",
        "type": "message"
      },
      {
        "content": [
          {
            "annotations": [],
            "logprobs": [],
            "text": "Solve a differential equation by identifying its type and applying the matching method.\n\nCommon workflow:\n1. Put it in a standard form.\n2. Classify it: ordinary or partial, first-order or higher-order, linear or nonlinear, separable, exact, etc.\n3. Choose a method that fits the class.\n4. Integrate or transform the equation.\n5. Apply initial or boundary conditions to find constants.\n6. Check the result by substituting it back into the original equation.\n\nCommon methods:\n- Separable equations: separate variables, then integrate.\n- Linear first-order equations: use an integrating factor.\n- Exact equations: verify exactness, then find a potential function.\n- Homogeneous or substitution-based equations: use a change of variables.\n- Higher-order linear equations with constant coefficients: solve the characteristic equation.\n- Nonhomogeneous linear equations: use undetermined coefficients or variation of parameters.\n- Systems of equations: use elimination, eigenvalues/eigenvectors, or matrix methods.\n- PDEs: use separation of variables, transforms, or characteristics, depending on the equation.\n\nExample:\nFor\n$$\n\\frac{dy}{dx} = ky\n$$\nthe general solution is\n$$\ny = Ce^{kx}.\n$$\n\nIf you want, I can give a very short “cheat sheet” for the main equation types.",
            "type": "output_text"
          }
        ],
        "id": "fVdiuI0NGQ5ZmcQktMTqus6ls2Ir9KfyEhv8+f+xa+D3zoXWzhWvixIR4DmccHQIw7kUpdkrBU8DSDVBsqnCfjvbwQs7PMjFiqtuN/0apwmPS5S4HSJpqO4ctVErc5dRoX+4H7h1AsI+o0mI/9UtgL388L5JffRUpm4D23HTnt3O9MY2Lv5oa0M4W2LxlJrpQ/pE5k83+OIOlUUrJt0zGfmst2osJ1v11d+HSaumrNPqwWaN8xxHpaplDNcxdc5FUTM/bbARIIM6rMK3rvkuYa5C4j1f/3ALzC8nJmVswNkbQ1DzLACySadPvlzJhIVPzx1HoHy43Ww/UsqKJh1O2dOvccFN+V+VCfXo+0Kaya30xGAFBUayLTrKXTkgyc0NJHiss0Qhnbg7b0yKRqQ+7gQ=",
        "phase": "final_answer",
        "role": "assistant",
        "status": "completed",
        "type": "message"
      }
    ],
    "parallel_tool_calls": true,
    "presence_penalty": 0,
    "previous_response_id": null,
    "prompt_cache_retention": "in_memory",
    "reasoning": {
      "effort": "medium",
      "summary": "detailed"
    },
    "safety_identifier": "59fa78d9eea528f4a1d5ee30e2d30de280d7f96e01920c692d593317cbe03d58",
    "service_tier": "default",
    "status": "completed",
    "store": false,
    "temperature": 1,
    "text": {
      "format": {
        "type": "text"
      },
      "verbosity": "medium"
    },
    "tool_choice": "auto",
    "tools": [
    ],
    "top_logprobs": 0,
    "top_p": 0.98,
    "truncation": "disabled",
    "usage": {
      "input_tokens": 23547,
      "input_tokens_details": {
        "cached_tokens": 3584
      },
      "output_tokens": 299,
      "output_tokens_details": {
        "reasoning_tokens": 0
      },
      "total_tokens": 23846
    },
    "user": null
  },
  "sequence_number": 300,
  "type": "response.completed"
}

[ulugbekna]

I think we should handle response.output_text.done to avoid hangs.

But I think it may also be a CAPI-side bug that there's such a lag for response. output_item.done to come

[ulugbekna]

Investigation Results: ~12s delay after last token in Responses API streams

Root Cause

The ~12 second delay between the last response.output_text.delta and response.content_part.done is caused by OpenAI's server-side post-generation content safety checks. The safety_identifier field in response.completed confirms this. copilot-api is a pure passthrough (confirmed by tracing the stream pipeline in copilot-api).

Why Tokens Appear Stuck

In OpenAIResponsesProcessor.push() (extensions/copilot/src/platform/endpoint/node/responsesApi.ts), there is no case for response.output_text.done or response.content_part.done — they fall through the switch silently.

Between the last response.output_text.delta (which IS handled and forwarded via onProgress) and response.output_item.done (which arrives ~12s later bundled with response.completed), no onProgress calls are made. The progressive renderer's typewriter timer catches up to all available words and cancels itself. Since isComplete is still false, the UI continues showing streaming indicators for ~12 seconds after the last token was actually received.

Evidence from Stream Dump

Output item	Event gap (output_text.done → content_part.done)
#0 (commentary, 78 chars)	30 ms
#1 (final_answer, ~1400 chars)	11.7 seconds

All closing events (content_part.done, output_item.done, response.completed) arrive within 23 ms of each other, confirming they were released as a batch after safety checks completed.

Fix Plan

Target file: extensions/copilot/src/platform/endpoint/node/responsesApi.ts — OpenAIResponsesProcessor.push()

Option A (preferred — signal text-stream completion early):

1. Add case 'response.output_text.done': to the switch statement.
2. Call onProgress with a signal indicating text generation is complete for the current output item (e.g., { text: '', textStreamDone: true }).
3. Add an optional textStreamDone?: boolean field to the IResponseDelta interface in extensions/copilot/src/platform/networking/common/fetch.ts.
4. In the rendering pipeline (progressive renderer in src/vs/workbench/contrib/chat/browser/widget/chatListRenderer.ts), respect this signal to stop showing streaming indicators immediately instead of waiting for response.completed.

Option B (simpler — fire empty progress to re-trigger render):

Since text deltas are already forwarded immediately via onProgress, and the progressive renderer already renders them, the visible issue is the streaming indicator persisting. Handling response.output_text.done by firing an empty onProgress call would cause the model's onDidChange to fire, re-trigger renderElement, and let the progressive renderer do another pass — potentially enough to drop the indicator.

Existing Test

A test at extensions/copilot/src/platform/endpoint/node/test/responsesApi.spec.ts already proves that response.output_text.done and response.content_part.done produce zero onProgress calls today, confirming the gap in event handling.

[roblourens]

Thanks for the investigation. @dileepyavan owns this

[dileepyavan]

Thanks @ulugbekna for this detail investigation. Will take a look this week.

[ulugbekna]

Created an issue with CAPI regarding the hangs - https://github.com/github/copilot-api/issues/32568.

On client side, I wonder if we could flush chat rendering when we receive output_text.done instead of waiting for output_item.done which seems to come with latency.