[BUG] OpenCode Go deepseek-v4-flash returns HTTP 500 while mimo-v2.5 works

Description

Description

deepseek-v4-flash on OpenCode Go does not return a response in the
OpenCode client. A direct API request eventually returns HTTP 500.

The same API key, endpoint, machine, and network work correctly with
mimo-v2.5, which returns HTTP 200.

Steps to reproduce

curl -sS --max-time 90 \
  -D - \
  https://opencode.ai/zen/go/v1/chat/completions \
  -H "Authorization: Bearer REDACTED" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "deepseek-v4-flash",
    "messages": [
      {
        "role": "user",
        "content": "Reply exactly with: OK"
      }
    ],
    "stream": false
  }'

Actual Result

HTTP/1.1 500 Internal Server Error

{"type":"error","error":{"type":"error","message":"Internal server error"}}

Control test

Changing only the model to mimo-v2.5 returns HTTP 200 and:

{"message":{"role":"assistant","content":"OK"}}

Request information

Model: deepseek-v4-flash
Endpoint: /zen/go/v1/chat/completions
Time: 2026-08-04 14:23:31 GMT
CF-RAY: a25e368a4a736814-SEA
Stream: false
Tools: none
OpenCode Go China-hosted model opt-in: enabled

Environment

OS: Debian Linux
Client: OpenCode Desktop
Network: Clash/Mihomo proxy
IPv4 connection and TLS handshake succeed
/zen/go/v1/models returns HTTP 200
mimo-v2.5 completion returns HTTP 200

Plugins

none

OpenCode version

1.18.13

Steps to reproduce

curl -sS --max-time 90 \
  -D - \
  https://opencode.ai/zen/go/v1/chat/completions \
  -H "Authorization: Bearer REDACTED" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "deepseek-v4-flash",
    "messages": [
      {
        "role": "user",
        "content": "Reply exactly with: OK"
      }
    ],
    "stream": false
  }'

Screenshot and/or share link

No response

Operating System

Debian Linux 13.5

Terminal

QTerminal