OpenAI API / OpenAI API

OpenAI SDK streaming tool_call delta accumulation breaks with duplicate indexes in first chunk

Developers using OpenAI streaming API see corrupted tool_call outputs when the first chunk contains multiple tool_calls with duplicate index values. Includes evidence for OpenAI API troubleshooting demand.

Source-backed Last updated May 21, 2026 1 source Needs local verification

Category: OpenAI API
Error signature: accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 21, 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 OpenAI API, 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

accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state is a OpenAI API failure pattern reported for developers trying to developers using openai streaming api see corrupted tool_call outputs when the first chunk contains multiple tool_calls with duplicate index values.. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue #3201 in openai-python repo (label: bug). The _deltas.py accumulate_delta function has a subtle indexing bug that produces incorrect accumulated tool_calls. Affects all streaming consumers of Chat Completions and Responses API with tool calling. Still open. Category mapping: OpenAI SDK library bug → OpenAI API.

Common causes

GitHub issue #3201 in openai-python repo (label: bug). The _deltas.py accumulate_delta function has a subtle indexing bug that produces incorrect accumulated tool_calls. Affects all streaming consumers of Chat Completions and Responses API with tool calling. Still open. Category mapping: OpenAI SDK library bug → OpenAI API.

Quick fixes

Confirm the exact error signature matches accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state.
Check the OpenAI API 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 accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state exactly before applying the quick fix.
Compare the failing environment with OpenAI API 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 accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state mean in OpenAI API?

accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state indicates the workflow described by "OpenAI SDK streaming tool_call delta accumulation breaks with duplicate indexes in first chunk" failed in a OpenAI API context. Start by confirming the exact signature and the component that emitted it.

What should I check first for accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state?

Check whether this cause matches your environment: GitHub issue #3201 in openai-python repo (label: bug). The _deltas.py accumulate_delta function has a subtle indexing bug that produces incorrect accumulated tool_calls. Affects all streaming consumers of Chat Completions and Responses API with tool calling. Still open. Category mapping: OpenAI SDK library bug → OpenAI API.

Is the accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state guidance source-backed?

The "OpenAI SDK streaming tool_call delta accumulation breaks with duplicate indexes in first chunk" 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 accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state?

For "OpenAI SDK streaming tool_call delta accumulation breaks with duplicate indexes in first chunk", 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 accumulate_delta assumes indexed list entry's index field matches its physical position; multiple tool_calls entries with same index in first streamed chunk corrupts accumulated state?

For "OpenAI SDK streaming tool_call delta accumulation breaks with duplicate indexes in first chunk", collect the failing OpenAI API command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.