LiteLLM Proxy Throws 'Header value must be str or bytes, not float' Internal Server Error

What this error means

InternalServerError: Hosted_vllmException — Header value must be str or bytes, not float is a LiteLLM failure pattern reported for developers trying to fix litellm proxy internalservererror when extra headers contain float values. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Active GitHub issue (May 2026) reports LiteLLM proxy throws ‘InternalServerError: Hosted_vllmException — Header value must be str or bytes, not float’ when certain extra headers are present. Affects the latest stable version. Exact error signature is highly specific.

Common causes

• LiteLLM is a critical infrastructure proxy for LLM routing. When extra headers with float values cause the proxy to crash with ‘Header value must be str or bytes, not float’, it blocks all traffic through the proxy, affecting entire teams.
• Active GitHub issue (May 2026) reports LiteLLM proxy throws ‘InternalServerError: Hosted_vllmException — Header value must be str or bytes, not float’ when certain extra headers are present. Affects the latest stable version. Exact error signature is highly specific.

Quick fixes

1. Confirm the exact error signature matches InternalServerError: Hosted_vllmException — Header value must be str or bytes, not float.
2. Check the LiteLLM account, local tool state, and provider configuration involved in the failing workflow.
3. 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

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. 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.

Sources checked

• https://github.com/BerriAI/litellm/issues/27458

Evidence note: Active GitHub issue (May 2026) reports LiteLLM proxy throws ‘InternalServerError: Hosted_vllmException — Header value must be str or bytes, not float’ when certain extra headers are present. Affects the latest stable version. Exact error signature is highly specific.

Related errors

• LiteLLM ‘No deployments available’ misleading rate limit error
• LiteLLM RouterRateLimitError missing Retry-After header

FAQ

What should I check first?

Start with the exact InternalServerError: Hosted_vllmException — Header value must be str or bytes, not float text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed LiteLLM workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without InternalServerError: Hosted_vllmException — Header value must be str or bytes, not float.