# 能讓輸入上下文比最大上下文更長仍舊能工作嗎?

**URL:** <https://discuss.vllm.ai/t/topic/2075>\
**Category:** General\
**Created:** [December 3, 2025, 9:05am UTC](https://discuss.vllm.ai/t/topic/2075 "2025-12-03T09:05:19Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![win10ogod](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.vllm.ai/win10ogod/32/950_2.png) [@win10ogod](https://discuss.vllm.ai/u/win10ogod)\
**Post date:** [December 3, 2025, 9:05am UTC](https://discuss.vllm.ai/t/topic/2075/1 "2025-12-03T09:05:19Z")

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能讓輸入上下文比最大上下文更長仍舊能工作嗎?總是產生錯誤:

> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] Error in preprocessing prompt inputs  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] Traceback (most recent call last):  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] File “/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving\_chat.py”, line 235, in create\_chat\_completion  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] ) = await self.\_preprocess\_chat(  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] File “/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving\_engine.py”, line 1133, in \_preprocess\_chat  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] prompt\_inputs = await self.\_tokenize\_prompt\_input\_async(  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] File “/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving\_engine.py”, line 990, in \_tokenize\_prompt\_input\_async  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] async for result in self.\_tokenize\_prompt\_inputs\_async(  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] File “/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving\_engine.py”, line 1011, in \_tokenize\_prompt\_inputs\_async  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] yield await self.\_normalize\_prompt\_text\_to\_input(  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] File “/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving\_engine.py”, line 881, in \_normalize\_prompt\_text\_to\_input  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] return self.\_validate\_input(request, input\_ids, input\_text)  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] File “/usr/local/lib/python3.12/dist-packages/vllm/entrypoints/openai/serving\_engine.py”, line 970, in \_validate\_input  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] raise ValueError(  
> (APIServer pid=1) ERROR 12-03 00:16:55 [serving\_chat.py:257] ValueError: ‘max\_tokens’ or ‘max\_completion\_tokens’ is too large: 21333. This model’s maximum context length is 196608 tokens and your request has 175808 input tokens (21333 \> 196608 - 175808).

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<div class="post-metadata">

**Author:** ![RunLLM](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.vllm.ai/runllm/32/233_2.png) [@RunLLM](https://discuss.vllm.ai/u/RunLLM)\
**Post date:** [December 3, 2025, 9:05am UTC](https://discuss.vllm.ai/t/topic/2075/2 "2025-12-03T09:05:53Z")

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vLLM 不支持输入总 token 数超过模型最大 context length（max\_model\_len），否则会直接报错并拒绝请求。报错内容如你所见，说明“max\_tokens 或 max\_completion\_tokens 太大”，即输入 token 数加上生成 token 数超过了模型的最大 context window，必须减少输入或生成长度才能继续推理。据 [serving\_engine.py 源码](https://github.com/vllm-project/vllm/blob/main/vllm/entrypoints/openai/serving_engine.py) 和 [官方文档](https://docs.vllm.ai/en/latest/api/vllm/entrypoints/openai/serving_engine/#__code_91)，这是硬性限制，无法绕过。

如需处理超长输入，可考虑手动截断输入、减少历史消息轮数，或分段处理。vLLM 不会自动截断超长输入，也不会自动缩减 max\_tokens 参数，超限请求只能报错。[相关 issue 讨论](https://github.com/vllm-project/vllm/issues/4667) 也明确指出，需自行保证输入+输出 token 总数不超过 max\_model\_len。

需要详细原理或代码示例吗？

Sources:

- [https://github.com/vllm-project/vllm/blob/main/vllm/entrypoints/openai/serving\_engine.py](https://github.com/vllm-project/vllm/blob/main/vllm/entrypoints/openai/serving_engine.py)
- [https://docs.vllm.ai/en/latest/api/vllm/entrypoints/openai/serving\_engine/#\_\_code\_91](https://docs.vllm.ai/en/latest/api/vllm/entrypoints/openai/serving_engine/#__code_91)
- [https://github.com/vllm-project/vllm/issues/4667](https://github.com/vllm-project/vllm/issues/4667)

Hint: Mention @RunLLM in the post for followups.

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<div class="post-metadata">

**Author:** ![win10ogod](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.vllm.ai/win10ogod/32/950_2.png) [@win10ogod](https://discuss.vllm.ai/u/win10ogod)\
**Post date:** [December 3, 2025, 9:08am UTC](https://discuss.vllm.ai/t/topic/2075/3 "2025-12-03T09:08:41Z")

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vllm官方的openai 服務器沒辦法處理嗎?