Github Copilot - Gemini models caching issue

Type: Bug

Use any Gemini model (3.1 Pro, 3.6 Flash, 3.7 Flash) and try to hold multiturn conversation with it
Check agent debug logs
Expected: At least some tokens would be cached
Actual: 0.0% is cached. Caching with all other models works fine

VS Code version: Code 1.135.0 (08d4889f9ec4a1685d257b9b95de036c8e1ce1e5, 2026-08-25T14:26:52Z)
OS version: Windows_NT x64 10.0.26200
Modes:
Remote OS version: Linux x64 6.6.87.2-microsoft-standard-WSL2

System Info

|Item|Value|
|---|---|
|CPUs|Intel(R) Core(TM) Ultra 9 275HX (24 x 3072)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x8086, DEVICE=0x7d67 [Intel(R) Graphics], DRIVER_VENDOR=Intel, DRIVER_VERSION=32.0.101.8724 *ACTIVE*
GPU1: VENDOR= 0x10de, DEVICE=0x2d58 [NVIDIA GeForce RTX 5070 Laptop GPU], DRIVER_VERSION=32.0.15.9201
GPU2: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8972
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)|31.43GB (14.60GB free)|
|Process Argv|--crash-reporter-id 2a17e2cd-1d8a-4f18-8a31-f4cbe3e5a60a|
|Screen Reader|no|
|VM|0%|

|Item|Value|
|---|---|
|Remote|WSL: Ubuntu|
|OS|Linux x64 6.6.87.2-microsoft-standard-WSL2|
|CPUs|Intel(R) Core(TM) Ultra 9 275HX (24 x 0)|
|Memory (System)|15.34GB (13.19GB free)|
|VM|0%|
Extensions (17)

Name|Identifier|Author|Version
---|---|---|---
Jupyter Keymap|ms-toolsai.jupyter-keymap|ms-toolsai|1.1.2
Dev Containers|ms-vscode-remote.remote-containers|ms-vscode-remote|0.466.0
WSL|ms-vscode-remote.remote-wsl|ms-vscode-remote|0.104.3
Svelte Intellisense|ardenivanov.svelte-intellisense|ardenivanov|0.7.1
Markdown Preview Mermaid Support|bierner.markdown-mermaid|bierner|1.32.1
Ruff|charliermarsh.ruff|charliermarsh|2026.74.0
ESLint|dbaeumer.vscode-eslint|dbaeumer|3.0.34
DBCode - SQL & Database Client for Postgres, MySQL, MongoDB & more|dbcode.dbcode|dbcode|1.36.15
Bash IDE|mads-hartmann.bash-ide-vscode|mads-hartmann|1.43.0
Playwright Test for VSCode|ms-playwright.playwright|ms-playwright|1.1.19
Black Formatter|ms-python.black-formatter|ms-python|2026.6.0
Python Debugger|ms-python.debugpy|ms-python|2026.6.0
Python|ms-python.python|ms-python|2026.4.0
Python Environments|ms-python.vscode-python-envs|ms-python|1.36.0
Live Preview|ms-vscode.live-server|ms-vscode|0.4.20
Chat Customizations Evaluations|ms-vscode.vscode-chat-customizations-evaluations|ms-vscode|1.0.8
Svelte for VS Code|svelte.svelte-vscode|svelte|110.3.1

A/B Experiments

```
vsliv368:30146709
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31463988
aj953862:31281341
4f60g487:31327383
envsactivate1:31551504
cloudbuttont:31379625
3efgi100_wstrepl:31403338
ec5jj548:31422691
cp_cls_t_966_ss:31526232
4je02754:31466945
c3h7c220:31478652
ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_c_1081:31454833
conptydll_true:31498968
e9c30283:31461165
test_treatment2:31471001
c9b86496:31447327
control_6dc23131:31555649
ei9d7968:31496641
nes-extended-on:31455476
chat:31457767
8hig5102:31480529
89g7j272:31518289
i2gc6536:31499202
52612955:31516516
h08i8180:31475369
23c7c724:31520045
ddid_c:31478207
hmra_i5g22:31518061
7df3h592:31512476
cp_cls_t_1082:31535311
logging_enabled_new:31498466
j0d79568:31499440
jb_cp_cls_t_632:31543129
56dj4588:31512888
32d76977:31512328
ha629193:31508444
jh5f2457_c:31540921
jbcp_cls_pctr_t:31531130
61138546:31518536
cp_intellij_t_nes:31548657
jf4hg949:31526829
ahp-both-windows:31556933
session_8:31532895
ihg5j128:31534457
f412h606:31551416
7g2b5551:31542111
enable_editor_pane_layout:31569726
allow-none:31555437
6i51c363:31551401
36h42362:31564511
c7c27ce7:31554789
1h923230:31564177
0dg73464:31554319
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
0d8dfbc3:31570291
a1hcc538:31559322
maidictation:31565333
0c1h4866:31566224
vrbsty_tr:31561058
session-mark-done:31558131
5b8j3302:31564601
mangle-name-treatment:31572634
permission_prompt_control:1332567
ccr_pr_nudge_control:1319470
vsc_wsm_t:1340632

```