Agent mode failed halfway through modifying files with a 400 Bad Request

[sean-mcmanus]

Type: Bug

I added 15 strings at the end of a .json file and it was halfway through adding those same strings to 12 other files in the same folder when it failed with a 400 Bad Request: Request id: f24fd3b1-b3fd-4893-b711-252919051528. The final result can be seen at microsoft/vscode-cpptools#13756 , in which 1 file was modified by myself and Copilot did the rest (but I had to fix the half the files due to the 400 Bad Request). Using GPT-4.1.

Extension version: 0.30.2025071101
VS Code version: Code - Insiders 1.103.0-insider (2eeceaa, 2025-07-11T05:03:59.670Z)
OS version: Windows_NT x64 10.0.26100
Modes:

System Info

Item	Value
CPUs	AMD EPYC 7763 64-Core Processor (16 x 2445)
GPU Status	2d_canvas: unavailable_software canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: disabled_software multiple_raster_threads: enabled_on opengl: disabled_off rasterization: disabled_software raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: disabled_software video_encode: disabled_software vulkan: disabled_off webgl: unavailable_software webgl2: unavailable_software webgpu: unavailable_software webnn: unavailable_software
Load (avg)	undefined
Memory (System)	63.95GB (28.60GB free)
Process Argv	--crash-reporter-id ce99d8db-1bb2-4e20-a916-dd8e74189cf1
Screen Reader	no
VM	0%

A/B Experiments

vsliv368:30146709
vspor879:30202332
vspor708:30202333
vspor363:30204092
pythonvspyt551:31249597
c4g48928:30535728
vscrpc:30624061
962ge761:30841072
h48ei257:31000450
cppperfnew:30980852
dwnewjupyter:31046869
nativeloc1:31118317
dwcopilot:31158714
5b1c1929:31184661
471b6256:31240254
6074i472:31201624
dwoutputs:31242946
9064b325:31222308
copilot_t_ci:31333650
g012b348:31231168
pythoneinst12:31251391
c7cif404:31309980
pythonpulldiag:31287486
6gi0g917:31259950
996jf627:31264550
pythonrdcb7:31268811
usemplatestapi:31297334
e6194696:31317039
747dc170:31275146
pythonpcpt1:31345880
6518g693:31302842
generatesymbolt:31280541
convertfstringf:31280702
9d2cg352:31346308
j97ad248:31306657
usemarketplace:31343026
0g1h6703:31329154
nes-emitfast-1:31333560
replacestringexc:31346310
onetestforazureexpcf:31335614
6abeh943:31336334
envsdeactivate2:31343187
0927b901:31340060
4gdec884:31342391
editstats-enabled:31346256

[vs-code-engineering]

This issue is a duplicate of #253136. Please refer to that issue for updates and discussions. Feel free to open a new issue if you think this is a different problem.

[sean-mcmanus]

Using GPT-4.1 failed a 2nd time. Switching to Claude Sonnet 4 worked. From the logging, it looks like GPT-4.1 was trying to send too much data.