LiteLLM / LiteLLM

LiteLLM Additional Drop Params Ignored on Anthropic Pass-Through

Fix LiteLLM not stripping unsupported parameters before forwarding to Bedrock Includes evidence for LiteLLM troubleshooting demand.

Source-backed Last updated May 15, 2026 1 source Needs local verification

Category: LiteLLM
Error signature: additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 15, 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

additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields is a LiteLLM failure pattern reported for developers trying to fix litellm not stripping unsupported parameters before forwarding to bedrock. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

6 reactions. additional_drop_params config ignored on Anthropic pass-through handler. Bedrock rejects unsupported fields.

Common causes

LiteLLM proxy forwards unsupported fields to Bedrock which rejects them, causing request failures for Claude Code users behind LiteLLM
6 reactions. additional_drop_params config ignored on Anthropic pass-through handler. Bedrock rejects unsupported fields.

Quick fixes

Confirm the exact error signature matches additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields.
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 additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields 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 additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields mean in LiteLLM?

additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields indicates the workflow described by "LiteLLM Additional Drop Params Ignored on Anthropic Pass-Through" failed in a LiteLLM context. Start by confirming the exact signature and the component that emitted it.

What should I check first for additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields?

Check whether this cause matches your environment: LiteLLM proxy forwards unsupported fields to Bedrock which rejects them, causing request failures for Claude Code users behind LiteLLM

Is the additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields guidance source-backed?

The "LiteLLM Additional Drop Params Ignored on Anthropic Pass-Through" 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 additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields?

For "LiteLLM Additional Drop Params Ignored on Anthropic Pass-Through", 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 additional_drop_params ignored for POST /v1/messages — Bedrock rejects unsupported fields?

For "LiteLLM Additional Drop Params Ignored on Anthropic Pass-Through", 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.