LanguageModelError - NotFound

Type: Bug

Running into instability with the provided chat.json config for BYOK. Model will run and then repeatedly fault with file instability as per log:

```
2026-07-31 11:22:02.410 [info] [AutomaticInstructionsCollector] Core vs extension instructions match (1 entries)
2026-07-31 11:22:02.417 [error] LanguageModelError: azure/Azure/gpt-5.6-terra
at i.NotFound (file:///c:/Users/charl/AppData/Local/Programs/Microsoft%20VS%20Code/e4c7e7b1d6/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:533:76115)
at Object.countTokens (file:///c:/Users/charl/AppData/Local/Programs/Microsoft%20VS%20Code/e4c7e7b1d6/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:537:47994)
at oft._textTokenLength (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:6889:8083)
at oft._countObjectTokens (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:6889:8673)
at oft.countToolTokens (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:6889:8476)
at e4.buildPrompt (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:2907:10343)
at async ZRe.buildPrompt (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:2901:5882)
at async ZRe.buildPrompt2 (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:1800:20802)
at async ZRe.runOne (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:1800:11773)
at async ZRe._runLoop (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:1800:5934)
at async c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:1800:4114
at async c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:6271:63017
at async iS.runWithToolCalling (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:2901:11)
at async iS.getResult (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:2900:1912)
at async eBe.getResult (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:2905:10132)
at async ix.handleRequest (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:2907:6378)
at async r4.getResult (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:2917:9180)
at async Gw._requestHandler (c:\Users\charl\AppData\Local\Programs\Microsoft VS Code\e4c7e7b1d6\resources\app\extensions\copilot\dist\extension.js:6885:1738)
at async i.$invokeAgent (file:///c:/Users/charl/AppData/Local/Programs/Microsoft%20VS%20Code/e4c7e7b1d6/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:562:21334)
```

Model is available at chatLanguageModels.json

```
{
"name": "Azure",
"vendor": "azure",
"apiKey": "${input:chat.lm.secret.***}",
"models": [
{
"id": "gpt-5.6-terra",
"name": "Azure GPT-5.6 Terra",
"url": "https://***/openai/v1/responses",
"toolCalling": true,
"vision": true,
"thinking": true,
"supportsReasoningEffort": [
"minimal",
"low",
"medium",
"high"
],
"reasoningEffortFormat": "responses",
"maxInputTokens": 128000,
"maxOutputTokens": 16000
}
]
},
```

VS Code version: Code 1.131.0 (e4c7e7b1d6d060162f4aa7f8225271b67ce1df75, 2026-07-28T10:51:25Z)
OS version: Windows_NT x64 10.0.26200
Modes:

System Info

|Item|Value|
|---|---|
|CPUs|AMD Ryzen 9 6900HX with Radeon Graphics (16 x 3294)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x1002, DEVICE=0x1681 [AMD Radeon(TM) Graphics], DRIVER_VENDOR=AMD, DRIVER_VERSION=32.0.21037.1004 *ACTIVE*
GPU1: VENDOR= 0x10de, DEVICE=0x24e0 [NVIDIA GeForce RTX 3070 Ti Laptop GPU], DRIVER_VERSION=32.0.15.9608
GPU2: VENDOR= 0x1002, DEVICE=0x1681 [AMD Radeon(TM) Graphics], DRIVER_VERSION=32.0.21037.1004
GPU3: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8875
Machine model name:
Machine model version:
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: disabled_off
trees_in_viz: disabled_off
video_decode: enabled
video_encode: enabled
webgl: enabled
webgpu: enabled
webnn: disabled_off|
|Load (avg)|undefined|
|Memory (System)|15.24GB (1.86GB free)|
|Process Argv|--crash-reporter-id 79701cd0-a598-4e31-8f42-e2728d9247e2|
|Screen Reader|no|
|VM|0%|
Extensions (10)

Name|Identifier|Author|Version
---|---|---|---
Azure Resource Explorer for VsCode|az-resource-explorer-vscode.azure-resource-explorer-for-vscode|az-resource-explorer-vscode|1.6.0
Azure Functions|ms-azuretools.vscode-azurefunctions|ms-azuretools|1.22.0
Azure Resources|ms-azuretools.vscode-azureresourcegroups|ms-azuretools|0.12.7
Bicep|ms-azuretools.vscode-bicep|ms-azuretools|0.46.1
C# Dev Kit|ms-dotnettools.csdevkit|ms-dotnettools|3.20.199
C#|ms-dotnettools.csharp|ms-dotnettools|2.140.9
.NET Install Tool|ms-dotnettools.vscode-dotnet-runtime|ms-dotnettools|3.1.0
VS Code Speech|ms-vscode.vscode-speech|ms-vscode|0.16.0
Codex – OpenAI’s coding agent|openai.chatgpt|openai|26.727.40816
Graphviz Interactive Preview|tintinweb.graphviz-interactive-preview|tintinweb|0.3.5

A/B Experiments

```
vsliv368cf:30146710
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31463988
aj953862:31281341
b6b4d950:31327385
envsactivate1:31551504
478i5457:31544283
cloudbuttont:31379625
3efgi100_wstrepl:31403338
ec5jj548:31422691
lysithea-0014-2in1-kld2:31558770
cp_cls_t_966_ss:31526232
4je02754:31466945
c3h7c220:31478652
cp_cls_c_1081:31454833
conptydll_true:31498968
e9c30283:31461165
test_treatment2:31471001
46204921:31447328
capico_axe_098a3278:31555651
idci7584:31464702
e3e4d672:31494082
ei9d7968:31496641
nes-extended-on:31455476
chat:31457767
8hig5102:31480529
89g7j272:31518289
7e187181:31503455
i2gc6536:31499202
52612955:31516516
ghj88844:31499326
ddid_t:31478206
hmra_i5g22:31518061
7df3h592:31512476
cp_cls_t_1082:31535311
logging_enabled_new:31498466
db5d2638:31499441
jb_cp_cls_t_632:31543129
56dj4588:31512888
32d76977:31512328
ha629193:31508444
cdk-lw-on:31524445
f9bf7985:31543584
jh5f2457_c:31540921
g4a0e106:31529594
8hfba999:31537718
jbcp_cls_pctr_t:31531130
61138546:31518536
cp_intellij_t_nes:31548657
gf14b233:31526830
nes-curr-leftover-1500:31538366
ahp-both-windows:31556933
h561g132:31533256
sessions_3:31532893
chatquotatrajectorynudge-control:31548766
ihg5j128:31534457
f412h606:31551416
9gg7f176:31542112
5fe6f778:31554331
allow-none:31555437
6i51c363:31551401
c7c27ce7:31554789
nes-gb3-5k:31554348
8hc4g144:31558143
1532g621_copy:31554320
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
session-archive:31558132

```