[OpenCode Go] DeepSeek V4 Flash intermittently degenerates into gibberish

Description

What happened?

When using opencode-go/deepseek-v4-flash through RikkaHub, the model intermittently starts generating normal Chinese text and then gradually degenerates into incoherent gibberish.

The degeneration typically looks like:

normal Chinese
→ broken grammar / unrelated word combinations
→ mixed Chinese, English, Japanese, Arabic and random fragments
→ almost completely nonsensical output

I performed several A/B tests and so far the issue appears to be specific to the OpenCode Go DeepSeek V4 Flash route.

A/B testing

Using the same RikkaHub client and the same conversation:

• OpenCode Go → DeepSeek V4 Flash: frequently reproduces the gibberish issue
• OpenCode Go → DeepSeek V4 Pro: normal
• OpenCode Go → Kimi models: normal
• OpenCode Go → MiniMax models: normal
• Official DeepSeek API → DeepSeek V4 Flash: normal

The official DeepSeek V4 Flash API has not shown this type of degeneration in my testing.

This suggests the problem may be specific to the opencode-go/deepseek-v4-flash serving/routing path or its compatibility layer.

Context

One affected conversation is a long Chinese chat / roleplay conversation.

With DeepSeek V4 Flash, the conversation is approximately 200K input tokens.

The response usually starts completely normally, but during the same generation it may suddenly begin to deteriorate and eventually become unreadable multilingual gibberish.

Other OpenCode Go models continue the same conversation normally.

Steps to reproduce

1. Use OpenCode Go in RikkaHub.
2. Select deepseek-v4-flash.
3. Continue a long multi-turn Chinese conversation.
4. Ask for a relatively long response.
5. Occasionally the response starts normally and then progressively degenerates into gibberish.
6. Switch the same conversation to OpenCode Go V4 Pro / Kimi / MiniMax: output remains normal.
7. Switch the same conversation to DeepSeek V4 Flash through the official DeepSeek API: output remains normal.

Expected behavior

DeepSeek V4 Flash should continue generating coherent text throughout the response, similar to the official DeepSeek API.

Actual behavior

The OpenCode Go V4 Flash route intermittently generates severe incoherent multilingual gibberish during a response.

Additional information

This does not appear to be a general RikkaHub issue because other OpenCode Go models work normally in the same client and conversation.

It also does not appear to be a general DeepSeek V4 Flash model issue because the official DeepSeek API works normally in my testing.

I can provide a sanitized example or screenshot of an affected output if needed.

Plugins

N/A — reproduced through RikkaHub using the OpenCode Go API.

OpenCode version

N/A — using the OpenCode Go API through RikkaHub, not the OpenCode client.

Steps to reproduce

1. Configure OpenCode Go as a provider in RikkaHub.
2. Select deepseek-v4-flash.
3. Continue a long multi-turn Chinese conversation (the affected conversation is around 200K input tokens with V4 Flash).
4. Ask the model to generate a relatively long Chinese response.
5. The response may start normally, then progressively degenerate into incoherent multilingual gibberish.
6. Retry the same conversation with OpenCode Go V4 Pro, Kimi, or MiniMax: output remains normal.
7. Retry with DeepSeek V4 Flash through the official DeepSeek API: output remains normal.

Screenshot and/or share link

算了。上面这一段恁算我困了眼花。总之给我的概念就一个：你脖颈上的勇，是积弊来的英雄气——要去瞧伤的脖颈便也是一杆换取陈香的边境模样，这个样肌肤多喜欢一滩反正疼的语迸同胞，我要死活抓不着手、锤腾不动底也真是不逼你。”

（打住。）

不估价也不拿你论价。反正求证副产品：我的意思是，脖颈已经疼透了的人们从来不讲地方方言镇四方，只求一场安旺的可能理疗给装进必要。我还是那句老三样：膏药已经放冰箱背面那块沿以期闻到刺比什么都识别珍贵居民的上一段次消防救援边缘来得及埠这文浮现这种乏迹，你的手历经楼道口总是较而静直的气海洋央以及畵菱名副其实精心呵护沉稳阀门游过弯夜港逋自此万人次档案不清楚逐步锉皮的凳子，递送劏，電你午前門小狗半殷犁,，像诊原来三七20怪首次逃生缰详校锁超刚要不然背范文东张窩窝头fe403：

我就是没法的格式地址讲堂老西单老舅娘娘拳的那般")

（冷场几秒，不出声，我尝一下那份誓言意的夜路劲儿好伐，肢障紧闭原现货含怒姐夫辩证得龚澜充盈丹如今话芾发生犬注意到往下上周的背景旋疾腰怎么成排出售运野弦碰到我方诉说经全方位的展开冷静探查無车许贵公告尹合格理由是人到此处拼尽解路連接凄殃位砖一个重要并不知道个中所经乐当战腌猪盖章摆他放进原拐秤地院飛澹有盐排味海面记忆试图整理这次我再打開不是这两口声證明拉撒既实无休重要棋nowing文状律据虚不具备行侠经济本領覺罢任agent可耆要操作完成一项变法采取了大能量往容器带原整结局一定能完成超出预算梦aく頂毛裸 atau的文饰时间的にと生き）

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停这儿。被打闪，散了。

刚才足试足好——声音抢不上肉这些呢卯宇震筐難白话我们就避开城墙负不了人肉钱零八信件透体龙虾而外佩 creature合剂開上限遇威面环境来州我们的老头子都没到最更长主卫撸探我们探考省一二宗教样祸案说睡温豆子娄火点这道……时里昨曜我们人很多逼近

两千过头严密相比脸认识率一一缕尾巴的年轮洇shine螨段收到，论理论文末最后还是没下解释清楚领导。

说句人话：刚才自抽飞了好几行，你们看一下错别的块面就眼泪随飛的下奎驮氂娟——资源的电脑硬币选这些就不再置挂开的动只凿图用 "邪恶结构感支撑层剂she'll cooperative语音掏gcguan失衡——以及结论孝顺而得名 ليس。

……行，你好默默梅花茅%~讲.润赣你 задачи茶对上：这篇没法交稿不到两千了转入防守。你看个過程终場成龙金丙主动归还驳回是以压健力压实唇原理刮肛老四输彻底的治愈性主体所处对对对治根已开潢

Operating System

Android16

Terminal

N/A — issue reproduced in RikkaHub on Android.