Name and Version

ggml_vulkan: Found 2 Vulkan devices:
ggml_vulkan: 0 = AMD Radeon RX 7600 XT (RADV NAVI33) (radv) | uma: 0 | fp16: 1 | bf16: 0 | warp size: 64 | shared memory: 65536 | int dot: 1 | matrix cores: KHR_coopmat
ggml_vulkan: 1 = AMD Radeon RX 7900 XTX (RADV NAVI31) (radv) | uma: 0 | fp16: 1 | bf16: 0 | warp size: 64 | shared memory: 65536 | int dot: 1 | matrix cores: KHR_coopmat
version: 8233 (c5a7788)
built with GNU 15.2.1 for Linux x86_64

Operating systems

Linux

GGML backends

HIP, Vulkan

Hardware

• Strix Halo
• Xeon Platinum 8368 + Radeon RX 7900 XTX

Models

Issue verified to affect at least:

• Qwen3.5 35B, 122B, 397B
• Step 3.5 Flash
• gpt-oss-120b

At various quants.

Problem description & steps to reproduce

I started seeing parser errors last night, and it seems to be related to the max_tokens param, but it seems to be linked to the max_tokens parameters:

curl -X POST -H "Content-Type: application/json" --data '{"model": "gpt-oss-120b", "messages": [{"role": "user", "content": "Warmup Warmup Warmup Warmup Warmup Warmup Warmup Warmup Warmup Warmup "}], "max_tokens": 1}' http://127.0.0.1:10011/v1/chat/completions

Fails for all models I've tried with an errors like this:

gpt-oss-120b:

{"error":{"code":500,"message":"Failed to parse input at pos 0: <|channel|>","type":"server_error"}}

Qwen3.5:

{"error":{"code":500,"message":"Failed to parse input at pos 8: ","type":"server_error"}}

Removing the max_tokens fixes it for all models. For gpt-oss-120b, increasing it to 3 also fixes it (2 does not). For Qwen3-397B-A17B (unsloth quants), no value of max_tokens seems to be sufficient in my trials, and I ended up having to filter out max_tokens using llama-swap for now, but obviously this is not desirable.

Might be related to #18675

First Bad Commit

c5a7788 (could have been an issue before, haven't had time to bisect)

Relevant log output

No relevant output in logs