Cursor OpenAI Compatible API Setup: Base URL, Model Names, and Usage Logs

Cursor OpenAI compatible API setup looks simple if you only think about three fields: API key, base URL, and model name. In practice, Cursor is a higher-level coding tool with its own model picker, usage accounting, team controls, and prompt-building path, so the safer setup is a verification workflow rather than a blind copy-paste.

As of the current public Cursor API key docs checked on July 8, 2026, Cursor documents Bring Your Own API Key for named providers in Cursor Settings > Models. It documents OpenAI, Anthropic, Google, Azure OpenAI, and AWS Bedrock keys; it also says custom API keys work with chat models only, Tab completion keeps using Cursor built-in models, and own-key requests still pass through Cursor servers for final prompt building. The public docs do not document a general arbitrary OpenAI-compatible base URL field.

That matters for Flatkey users. Flatkey gives teams one key, an OpenAI-compatible gateway at https://router.flatkey.ai/v1, model access across providers, and usage and cost review in one place. If your Cursor build, admin policy, or provider configuration exposes a custom OpenAI base URL field, use this guide to validate the setup. If your Cursor UI only supports provider-owned API keys, use the same checks to decide when to keep Cursor on its documented provider flow and use Flatkey in tools that explicitly expose a custom base URL, such as Cline or Claude Code router workflows.

The goal is not to force every Cursor request through a gateway. The goal is to make every Cursor OpenAI compatible API decision inspectable: who owns the key, which base URL is actually used, which model name is selected, where usage appears, and how to roll back.

Cursor OpenAI compatible API setup: what to verify first

Start with a short decision table before changing any setting.

Setup surface	What Cursor publicly documents	What you must verify in your workspace
Provider API key	Add a key in Cursor Settings > Models for supported providers.	Which provider row you are editing, who owns the key, and whether team policy allows BYOK.
Custom base URL	Cursor public docs checked on July 8, 2026 do not document a general arbitrary OpenAI-compatible base URL path.	Whether your installed Cursor version or enterprise configuration exposes a base URL override.
Model names	Cursor models appear in the model picker; availability depends on plan, provider, and region.	Whether the selected model name is a Cursor model, a provider model, or a gateway model alias.
Usage logs	Cursor usage dashboard shows usage, allowance, on-demand charges, cost, and model selection for Cursor usage.	Whether a request also appears in Flatkey logs, provider logs, or only Cursor usage.
Privacy mode	Cursor says Zero Data Retention does not apply when you use your own API keys.	Whether your security review accepts Cursor prompt-building plus the chosen provider or gateway path.

This is the first rule of Cursor OpenAI compatible API setup: do not treat an API key field as proof of a gateway route. A key field proves credential entry. A base URL field, request log, and usage record prove routing.

The values to collect before touching Cursor

Put the setup values in a small worksheet. Share this with the person who owns billing or security, not just the developer doing the UI change.

Field	Flatkey example	Why it matters
API key owner	A dedicated Flatkey key for Cursor evaluation	Separates IDE traffic from app traffic and makes rollback clean.
Base URL	https://router.flatkey.ai/v1	Avoids duplicate /v1/v1 paths and keeps the route OpenAI-compatible.
Endpoint family	Chat Completions first	Cursor BYOK docs say custom API keys work with chat models only.
Model name	Current Flatkey catalog alias selected by the team	Gateway aliases can differ from Cursor model-picker names.
Test prompt	One low-risk Agent or chat prompt	Keeps the first request easy to find in logs.
Usage owner	Cursor usage page, Flatkey usage/logs, finance owner	Prevents surprise billing disputes after the test.
Rollback value	Previous Cursor model/key setting	Lets the team revert without deleting evidence.

For a Cursor OpenAI compatible API test, the most common mistake is using a model display name from one system in another system. Cursor model names, provider model IDs, and Flatkey route aliases are not automatically interchangeable. Pick the model name from the place that will receive the request.

Run an external smoke test first

Before testing inside Cursor, validate the gateway values outside Cursor. These snippets are templates only; replace the key and model with values from your current Flatkey account and catalog.

export FLATKEY_API_KEY="sk-fk-..."
export FLATKEY_MODEL="your-current-model-alias"

curl -sS https://router.flatkey.ai/v1/models \
  -H "Authorization: Bearer $FLATKEY_API_KEY"

Use the models response to confirm the exact model ID or alias. Then test the chat path:

curl -sS https://router.flatkey.ai/v1/chat/completions \
  -H "Authorization: Bearer $FLATKEY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "'"$FLATKEY_MODEL"'",
    "messages": [
      {
        "role": "user",
        "content": "Reply with exactly: cursor route probe ok"
      }
    ]
  }'

Save the request timestamp, model name, HTTP status, response body, and usage object if the response includes one. OpenAI's Chat Completions API shape is built around model and messages, and successful responses can include token usage. OpenAI's models endpoint lists currently available models for an account. Those two facts make this smoke test useful before you involve Cursor.

If this external test fails, do not continue to Cursor. Fix the key, model alias, quota, or endpoint family first. A failed external test will not become easier to debug after Cursor adds its own model picker, prompt building, and request path.

Configure Cursor only after the route is proven

Now open Cursor and inspect the actual settings available to your account.

1. Open Cursor Settings > Models.
2. Check whether your organization allows personal API keys. Enterprise admins can restrict BYOK usage.
3. If you are using Cursor's documented BYOK path, choose the provider row Cursor supports and enter that provider's key.
4. If your Cursor environment exposes a custom OpenAI-compatible base URL field, enter only the base URL root, for example https://router.flatkey.ai/v1, not the full /chat/completions path.
5. Enter or select the model name from the receiving system. For Flatkey, use the model alias confirmed in the Flatkey catalog or /v1/models smoke test.
6. Save the setting, then select the target model in the Cursor model picker if Cursor exposes it there.

This is where the article title can mislead teams: Cursor OpenAI compatible API setup is not complete when the settings page saves. It is complete only when the request you send from Cursor appears in the expected usage trail.

A model-name checklist for Cursor model routing

Use this table when someone asks, "Which model name should I type?"

Question	Good evidence	Bad shortcut
Does Cursor expose the model in its picker?	The active model is visible in the chat or Agent panel.	Assuming a provider ID appears because the key was saved.
Does the gateway know the model alias?	/v1/models or the Flatkey catalog shows the alias for your account.	Copying a marketing model name from a blog post.
Does the endpoint family match?	Chat Completions route is selected for chat-model traffic.	Sending a native-only model through the wrong OpenAI-compatible path.
Does the model support your feature?	A saved test for plain chat, streaming, and tool calls if needed.	Treating plain text completion as proof of all features.
Can finance find it later?	Usage entry includes enough route/model context for review.	Relying only on a successful answer in the editor.

For a Cursor OpenAI compatible API rollout, start with plain chat. Do not use a large codebase refactor, tool-heavy Agent run, or long Max Mode session as the first test. Make the first prompt boring enough that the usage record is the main result.

Verify usage logs in three places

A gateway setup that returns text but leaves no usage trail is not production-ready. Check three layers after the first request.

Layer	What to check	Owner
Cursor usage	Cursor dashboard usage, model selection, allowance, and on-demand charges.	Cursor seat owner or team admin.
Flatkey usage/logs	Request timestamp, key, model alias, endpoint family, token usage, cost context, and errors where available.	Platform or operations owner.
Provider or gateway response	HTTP status, response usage, model field, and any request ID or error code.	Developer doing the smoke test.

The important ownership detail is that Cursor's own docs say your API key is sent to Cursor's backend with every own-key request for final prompt building. That means a Cursor OpenAI compatible API test should be reviewed as a tool-plus-gateway path, not as a direct local call from your laptop to the provider.

If your team relies on Cursor Zero Data Retention, read the Cursor BYOK privacy note before using your own key. Cursor states that its Zero Data Retention policy does not apply when using your own API keys; data handling follows the chosen provider's policy. If you route through Flatkey, add Flatkey's current policy, dashboard, and retention evidence to the same review packet.

Troubleshooting base URL, key, and model failures

Most failures fall into a small set of causes.

Symptom	Likely cause	Fix
401 or authentication error	Wrong key, copied whitespace, revoked key, or key not allowed for the route.	Recopy the key, use a dedicated test key, and retry the external curl first.
403 or permission error	Team policy, provider entitlement, region, or gateway permission blocks the request.	Check Cursor BYOK policy, Flatkey account access, and provider availability.
404 or model not found	Model name is not valid for the receiving system.	Use the model picker, /v1/models, or the current Flatkey catalog as the source of truth.
429 or quota error	Cursor plan allowance, provider quota, Flatkey quota, or request rate was exceeded.	Lower test volume, check limits, and assign an owner for quota increases.
Text returns but no Flatkey log appears	Request did not route through Flatkey.	Recheck whether Cursor accepted a custom base URL or only a provider key.
Cursor Tab behavior unchanged	Cursor documents that custom API keys only work with chat models.	Do not use Tab completion as the verification signal.

OpenAI's own error guide treats authentication, rate limit, quota, and overloaded service errors as different owner actions. Keep that separation in your Cursor runbook. A retry policy will not fix a wrong model name, and a new model name will not fix a BYOK policy block.

When not to use Flatkey for Cursor

There are times when the best Cursor OpenAI compatible API decision is to stop.

Do not route Cursor through Flatkey if your current Cursor build does not expose a base URL override and your workflow requires a true custom endpoint. Do not route Cursor through Flatkey if your enterprise admin has disabled personal API keys. Do not route Cursor through Flatkey if your security review depends on Cursor built-in-model privacy controls that do not apply to own-key traffic.

In those cases, keep Cursor on the documented provider path and use Flatkey where the client explicitly supports OpenAI-compatible base URLs: application SDKs, internal tools, evaluation scripts, Cline, Open WebUI, LangChain, LlamaIndex, or other integration surfaces. If you need the general migration pattern, start with the OpenAI-compatible API migration guide. For coding-agent router patterns, compare the Claude Code API router setup and the Cline OpenAI-compatible API setup.

Production checklist

Before calling the Cursor OpenAI compatible API setup complete, save this evidence:

Evidence	Complete when
Cursor setting	Screenshot or admin note shows the provider/key/base URL path used, with secrets hidden.
Model proof	The model name is sourced from Cursor's model picker, Flatkey catalog, or /v1/models, not a guess.
External smoke test	https://router.flatkey.ai/v1/chat/completions returns a plain response with the chosen model.
Cursor request proof	A small Cursor prompt used the intended model and did not rely on Tab completion.
Usage proof	Cursor usage and Flatkey usage/log evidence are saved with timestamps.
Error map	401, 403, 404, 429, and 5xx owner actions are documented.
Rollback	The previous Cursor model/key path is recorded and can be restored without deleting logs.

Cursor OpenAI compatible API setup is valuable when it turns coding-tool traffic into governed, reviewable model usage. Keep the base URL, model name, and usage-log proof together. When you need one gateway key and one place to review model traffic, get a Flatkey key, test a low-risk chat request first, and move only after the logs prove the route.