Non-streaming OpenAI API calls silently hang forever behind NAT — no TCP keepalive on default transport

What this error means

Non-streaming OpenAI API calls hang indefinitely behind NAT gateway — neither side knows connection is dead, no timeout exception raised, call blocks forever is a OpenAI API failure pattern reported for developers trying to fix openai sdk silent hangs caused by missing tcp keepalive, affecting deployments behind aws nat gateway, gcp cloud nat, and isp routers. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub openai-python #3269 (open, created 2026-05-19): httpx transport has no SO_KEEPALIVE, so NAT gateways silently drop idle TCP connections during long o-series/gpt-5.x reasoning calls taking 300–700s. Server generates response but client never receives it. Affects EKS, ECS, Cloud Run, GKE deployments and local dev behind routers. Fix: enable TCP keepalive on default transport. Category: OpenAI API.

Common causes

• GitHub openai-python #3269 (open, created 2026-05-19): httpx transport has no SO_KEEPALIVE, so NAT gateways silently drop idle TCP connections during long o-series/gpt-5.x reasoning calls taking 300–700s. Server generates response but client never receives it. Affects EKS, ECS, Cloud Run, GKE deployments and local dev behind routers. Fix: enable TCP keepalive on default transport. Category: OpenAI API.

Quick fixes

1. Confirm the exact error signature matches Non-streaming OpenAI API calls hang indefinitely behind NAT gateway — neither side knows connection is dead, no timeout exception raised, call blocks forever.
2. Check the OpenAI API account, local tool state, and provider configuration involved in the failing workflow.
3. Check the build output, project root, and deployment platform configuration before redeploying.

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/openai/openai-python/issues/3269

Evidence note: GitHub openai-python #3269 (open, created 2026-05-19): httpx transport has no SO_KEEPALIVE, so NAT gateways silently drop idle TCP connections during long o-series/gpt-5.x reasoning calls taking 300–700s. Server generates response but client never receives it. Affects EKS, ECS, Cloud Run, GKE deployments and local dev behind routers. Fix: enable TCP keepalive on default transport. Category: OpenAI API.

Related errors

• OpenAI API

FAQ

What should I check first?

Start with the exact Non-streaming OpenAI API calls hang indefinitely behind NAT gateway — neither side knows connection is dead, no timeout exception raised, call blocks forever text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed OpenAI API 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 Non-streaming OpenAI API calls hang indefinitely behind NAT gateway — neither side knows connection is dead, no timeout exception raised, call blocks forever.