LiteLLM / LiteLLM

LiteLLM strips reasoning_content from DeepSeek V4 Pro responses, breaking multi-turn conversations

Fix LiteLLM breaking DeepSeek V4 Pro multi-turn conversations by stripping reasoning_content Includes evidence for LiteLLM troubleshooting demand.

Source-backed Last updated May 14, 2026 1 source Needs local verification

Category: LiteLLM
Error signature: LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn)
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 14, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for LiteLLM, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

What this error means

LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn) is a LiteLLM failure pattern reported for developers trying to fix litellm breaking deepseek v4 pro multi-turn conversations by stripping reasoning_content. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

17 reactions. First turn succeeds, all subsequent turns fail with 400. Root cause: Message.__init__ in litellm/types/utils.py deletes reasoning_content when None. Old R1 behavior (strip) conflicts with V4 Pro requirement (preserve).

Common causes

DeepSeek V4 Pro requires reasoning_content to be passed back in multi-turn conversations, but LiteLLM strips it during serialization (carried over from R1 behavior)
17 reactions. First turn succeeds, all subsequent turns fail with 400. Root cause: Message.__init__ in litellm/types/utils.py deletes reasoning_content when None. Old R1 behavior (strip) conflicts with V4 Pro requirement (preserve).

Quick fixes

Confirm the exact error signature matches LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn).
Check the LiteLLM account, local tool state, and provider configuration involved in the failing workflow.
Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

Verify the command, editor, extension, or API client that produced the error.
Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

Capture the exact error message and the command, editor action, or request that triggered it.
Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
Review the source evidence below and compare it with your environment.
Apply one change at a time and rerun the smallest failing action.
Keep the working fix documented for the team or deployment environment.

How to prevent it

Keep provider/tool configuration documented.
Record non-secret diagnostics such as tool version, provider name, model name, and command path.
Add a lightweight check before CI or production workflows depend on the tool.

Diagnostic flow for this page

Match LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn) exactly before applying the quick fix.
Compare the failing environment with LiteLLM versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn) mean in LiteLLM?

LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn) indicates the workflow described by "LiteLLM strips reasoning_content from DeepSeek V4 Pro responses, breaking multi-turn conversations" failed in a LiteLLM context. Start by confirming the exact signature and the component that emitted it.

What should I check first for LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn)?

Check whether this cause matches your environment: DeepSeek V4 Pro requires reasoning_content to be passed back in multi-turn conversations, but LiteLLM strips it during serialization (carried over from R1 behavior)

Is the LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn) guidance source-backed?

The "LiteLLM strips reasoning_content from DeepSeek V4 Pro responses, breaking multi-turn conversations" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn)?

For "LiteLLM strips reasoning_content from DeepSeek V4 Pro responses, breaking multi-turn conversations", avoid applying "Compare the failing environment with a known working setup, then change one configuration value at a time." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging LiteLLM BadRequestError: reasoning_content must be passed back to the API (DeepSeek V4 Pro multi-turn)?

For "LiteLLM strips reasoning_content from DeepSeek V4 Pro responses, breaking multi-turn conversations", collect the failing LiteLLM command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.