[Bug]: For GPT OSS 120B: Expected 2 output messages (reasoning and final), but got 7.

[leoleoasd]

Your current environment

The output of python collect_env.py

Collecting environment information...
==============================
        System Info
==============================
OS                           : Ubuntu 22.04.5 LTS (x86_64)
GCC version                  : (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
Clang version                : Could not collect
CMake version                : version 3.22.1
Libc version                 : glibc-2.35

==============================
       PyTorch Info
==============================
PyTorch version              : 2.9.0.dev20250804+cu128
Is debug build               : False
CUDA used to build PyTorch   : 12.8
ROCM used to build PyTorch   : N/A

==============================
      Python Environment
==============================
Python version               : 3.12.11 (main, Jul 23 2025, 00:34:44) [Clang 20.1.4 ] (64-bit runtime)
Python platform              : Linux-5.10.228-219.884.amzn2.x86_64-x86_64-with-glibc2.35

==============================
       CUDA / GPU Info
==============================
Is CUDA available            : True
CUDA runtime version         : 12.2.140
CUDA_MODULE_LOADING set to   :
GPU models and configuration :
GPU 0: NVIDIA H200
GPU 1: NVIDIA H200
GPU 2: NVIDIA H200
GPU 3: NVIDIA H200
GPU 4: NVIDIA H200
GPU 5: NVIDIA H200
GPU 6: NVIDIA H200
GPU 7: NVIDIA H200

Nvidia driver version        : 550.127.05
cuDNN version                : Could not collect
HIP runtime version          : N/A
MIOpen runtime version       : N/A
Is XNNPACK available         : True

==============================
          CPU Info
==============================
Architecture:                         x86_64
CPU op-mode(s):                       32-bit, 64-bit
Address sizes:                        46 bits physical, 48 bits virtual
Byte Order:                           Little Endian
CPU(s):                               192
On-line CPU(s) list:                  0-191
Vendor ID:                            GenuineIntel
Model name:                           Intel(R) Xeon(R) Platinum 8488C
CPU family:                           6
Model:                                143
Thread(s) per core:                   2
Core(s) per socket:                   48
Socket(s):                            2
Stepping:                             8
BogoMIPS:                             4800.00
Flags:                                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss ht syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq monitor ssse3 fma cx16 pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch invpcid_single ssbd ibrs ibpb stibp ibrs_enhanced fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb avx512cd sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves avx512_bf16 wbnoinvd ida arat avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg tme avx512_vpopcntdq rdpid cldemote movdiri movdir64b md_clear serialize flush_l1d arch_capabilities
Hypervisor vendor:                    KVM
Virtualization type:                  full
L1d cache:                            4.5 MiB (96 instances)
L1i cache:                            3 MiB (96 instances)
L2 cache:                             192 MiB (96 instances)
L3 cache:                             210 MiB (2 instances)
NUMA node(s):                         2
NUMA node0 CPU(s):                    0-47,96-143
NUMA node1 CPU(s):                    48-95,144-191
Vulnerability Gather data sampling:   Not affected
Vulnerability Itlb multihit:          Not affected
Vulnerability L1tf:                   Not affected
Vulnerability Mds:                    Not affected
Vulnerability Meltdown:               Not affected
Vulnerability Mmio stale data:        Not affected
Vulnerability Reg file data sampling: Not affected
Vulnerability Retbleed:               Not affected
Vulnerability Spec rstack overflow:   Not affected
Vulnerability Spec store bypass:      Mitigation; Speculative Store Bypass disabled via prctl and seccomp
Vulnerability Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:             Mitigation; Enhanced / Automatic IBRS, IBPB conditional, RSB filling, PBRSB-eIBRS SW sequence
Vulnerability Srbds:                  Not affected
Vulnerability Tsx async abort:        Not affected

==============================
Versions of relevant libraries
==============================
[pip3] numpy==2.2.6
[pip3] nvidia-cublas-cu12==12.8.4.1
[pip3] nvidia-cuda-cupti-cu12==12.8.90
[pip3] nvidia-cuda-nvrtc-cu12==12.8.93
[pip3] nvidia-cuda-runtime-cu12==12.8.90
[pip3] nvidia-cudnn-cu12==9.10.2.21
[pip3] nvidia-cudnn-frontend==1.13.0
[pip3] nvidia-cufft-cu12==11.3.3.83
[pip3] nvidia-cufile-cu12==1.13.1.3
[pip3] nvidia-curand-cu12==10.3.9.90
[pip3] nvidia-cusolver-cu12==11.7.3.90
[pip3] nvidia-cusparse-cu12==12.5.8.93
[pip3] nvidia-cusparselt-cu12==0.7.1
[pip3] nvidia-ml-py==12.575.51
[pip3] nvidia-nccl-cu12==2.27.5
[pip3] nvidia-nvjitlink-cu12==12.8.93
[pip3] nvidia-nvshmem-cu12==3.3.9
[pip3] nvidia-nvtx-cu12==12.8.90
[pip3] pynvml==12.0.0
[pip3] pytorch-triton==3.4.0+git11ec6354
[pip3] pyzmq==27.0.1
[pip3] torch==2.9.0.dev20250804+cu128
[pip3] torchaudio==2.8.0.dev20250804+cu128
[pip3] torchvision==0.24.0.dev20250804+cu128
[pip3] transformers==4.55.0
[pip3] triton==3.4.0+git663e04e8
[pip3] triton_kernels==1.0.0
[conda] No relevant packages

==============================
         vLLM Info
==============================
ROCM Version                 : Could not collect
Neuron SDK Version           : N/A
vLLM Version                 : 0.10.2.dev2+gf5635d62e.d20250806 (git sha: f5635d62e, date: 20250806)
vLLM Build Flags:
  CUDA Archs: Not Set; ROCm: Disabled; Neuron: Disabled
GPU Topology:
  	GPU0	GPU1	GPU2	GPU3	GPU4	GPU5	GPU6	GPU7	CPU Affinity	NUMA Affinity	GPU NUMA ID
GPU0	 X 	NV18	NV18	NV18	NV18	NV18	NV18	NV18	0-47,96-143	0		N/A
GPU1	NV18	 X 	NV18	NV18	NV18	NV18	NV18	NV18	0-47,96-143	0		N/A
GPU2	NV18	NV18	 X 	NV18	NV18	NV18	NV18	NV18	0-47,96-143	0		N/A
GPU3	NV18	NV18	NV18	 X 	NV18	NV18	NV18	NV18	0-47,96-143	0		N/A
GPU4	NV18	NV18	NV18	NV18	 X 	NV18	NV18	NV18	48-95,144-191	1		N/A
GPU5	NV18	NV18	NV18	NV18	NV18	 X 	NV18	NV18	48-95,144-191	1		N/A
GPU6	NV18	NV18	NV18	NV18	NV18	NV18	 X 	NV18	48-95,144-191	1		N/A
GPU7	NV18	NV18	NV18	NV18	NV18	NV18	NV18	 X 	48-95,144-191	1		N/A

Legend:

  X    = Self
  SYS  = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI)
  NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node
  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
  PXB  = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge)
  PIX  = Connection traversing at most a single PCIe bridge
  NV#  = Connection traversing a bonded set of # NVLinks

==============================
     Environment Variables
==============================
NVIDIA_VISIBLE_DEVICES=GPU-506e4329-6727-0e70-c3e8-519b97d185d5,GPU-30a4e2e5-1896-ce9b-39e9-ac92304e8a6d,GPU-9003bb03-aa76-ddc2-b4d9-9861c388da18,GPU-a5db44bf-7a1f-a031-cd29-462634ca698f,GPU-1f47cee6-ed68-0aa0-e94e-bd8cb90dde18,GPU-93796833-fc01-1bd3-6a3a-df01fc2a4968,GPU-cf25f006-4b7a-f141-74bf-04967d86b84a,GPU-ebab81db-daa7-31e2-ae8e-cbcf7c9b5e3b
NVIDIA_REQUIRE_CUDA=cuda>=12.2 brand=tesla,driver>=470,driver<471 brand=unknown,driver>=470,driver<471 brand=nvidia,driver>=470,driver<471 brand=nvidiartx,driver>=470,driver<471 brand=geforce,driver>=470,driver<471 brand=geforcertx,driver>=470,driver<471 brand=quadro,driver>=470,driver<471 brand=quadrortx,driver>=470,driver<471 brand=titan,driver>=470,driver<471 brand=titanrtx,driver>=470,driver<471 brand=tesla,driver>=525,driver<526 brand=unknown,driver>=525,driver<526 brand=nvidia,driver>=525,driver<526 brand=nvidiartx,driver>=525,driver<526 brand=geforce,driver>=525,driver<526 brand=geforcertx,driver>=525,driver<526 brand=quadro,driver>=525,driver<526 brand=quadrortx,driver>=525,driver<526 brand=titan,driver>=525,driver<526 brand=titanrtx,driver>=525,driver<526
NCCL_SOCKET_IFNAME=eth0
NVIDIA_DRIVER_CAPABILITIES=compute,utility
NVIDIA_PRODUCT_NAME=CUDA
CUDNN_PATH=/workdir/.venv/lib/python3.10/site-packages/nvidia/cudnn
CUDA_VERSION=12.2.0
LD_LIBRARY_PATH=/usr/local/nvidia/lib:/usr/local/nvidia/lib64
NCCL_CUMEM_ENABLE=0
PYTORCH_NVML_BASED_CUDA_CHECK=1
TORCHINDUCTOR_COMPILE_THREADS=1

🐛 Describe the bug

Use the following prompt:

{
  "messages": [
  {
    "role": "system",
    "content": "You are an autonomous intelligent agent tasked with navigating a web browser to complete specific objectives. You have access to a simplified representation of the webpage and can perform various acti... [TRUNCATED]"
  },
  {
    "role": "user",
    "content": "URL: http://metis.lti.cs.cmu.edu:7770/\nTitle: One Stop Market\n\nHTML:\n<html><body data-container=\"body\" id=\"html-body\" data-is-focused=\"true\"><header><div><ul><li><a href=\"http://metis.lti.cs.cmu.edu:7... [TRUNCATED]"
  }
]
}

Will result in randomly 200, 400 and 500. Sometime it responds normally (it will say it don't know what to do because of the prompt os truncated), sometimes it returns 400 bad request:

{
  "object": "error",
  "message": "Expected 2 output messages (reasoning and final), but got 7.",
  "type": "BadRequestError",
  "param": null,
  "code": 400
}

and sometimes it returns 500 internal server error.

Before submitting a new issue...

• Make sure you already searched for relevant issues, and asked the chatbot living at the bottom right corner of the documentation page, which can answer lots of frequently asked questions.

[leoleoasd]

I think there are some errors in chat template parsing, and my weird(?) prompt will trigger a corner case.

[HackGiter]

I encountered the same issue when I tried to reproduce the AIME25 score on GPT-OSS-20B.

[devholic77]

I encountered the same issue gpt-oss-120b 😢

[liuqianchao]

same, sometimes got "500 Internal Server Error" for gpt oss 120B

[GanjinZero]

Same on gpt-oss-120b

[Dam930]

The problem also occurs with gpt-oss-20b (gpt oss 120B for me too), specifically in serving_chat.py on line 1065.

It seems that for me, three outputs are produced: analysis (reasoning), commentary (the actual function call), and final (a message that is usually unnecessary and often a hallucination).

[huanwojitui]

same error

[hnt2601]

I got same error

[xyz189411yt]

same error

[Kass123777]

Same error when running vllm serve openai/gpt-oss-20b.

[shloke-capsico]

Same error. When serving gpt-oss:120b via vllm+docker and inference with openai agents sdk.

[simonfl]

Similar, I've getting a lot of these using chat completions:
BadRequestError: Error code: 400 - {'object': 'error', 'message': 'Expected 2 output messages (reasoning and final), but got 3.', 'type': 'BadRequestError', 'param': None, 'code': 400}

[giuliohome]

Same issue here

vllm serve openai/gpt-oss-120b --host 0.0.0.0 --port 11434 --max_model_len 100000 --gpu_memory_utilization 0.9 --served-model-name gpt-oss-120b

and an openai agent sdk python code as client