Gemini native (/v1beta)

Endpoint

ALL /v1beta/*
x-goog-api-key: vk-lw-<ULID>

Every path under /v1beta is forwarded to Google as written: method, path, query string and body. The gateway does not translate the body and returns Google’s answer, headers included. It removes your client credential and the hop-by-hop headers, sends Google’s own credential in their place, and adds its own response headers. Authorization: Bearer <key> works in place of x-goog-api-key. This is the route for gemini-cli and the @google/genai SDK. Set GOOGLE_GEMINI_BASE_URL=https://gateway.langwatch.ai and use the virtual key as the Gemini API key; see Gemini CLI.

Request

curl https://gateway.langwatch.ai/v1beta/models/gemini-2.5-flash:generateContent \
  -H "x-goog-api-key: $LANGWATCH_VIRTUAL_KEY" \
  -H "Content-Type: application/json" \
  -d '{"contents": [{"role": "user", "parts": [{"text": "Hi"}]}]}'

Response

{
  "candidates": [
    {"content": {"role": "model", "parts": [{"text": "Hello!"}]}, "finishReason": "STOP"}
  ],
  "usageMetadata": {"promptTokenCount": 2, "candidatesTokenCount": 2, "totalTokenCount": 4}
}

Which credentials serve it

Only a Gemini or a Vertex credential. The body and the path are Google’s own, so no other provider can read them. A key with neither answers 400 model_provider_not_bound and no provider is called. A Vertex credential serves the request through Google’s Vertex path form.

What the gateway reads and changes

Part of the request	What the gateway does
The model in the path (`/models/{model}:{action}`)	Read as the model. Resolved through the key’s allowlist, policy rules and routing policy. Outside the routing policy: `403 policy_violation` with the message `model "<model>" is not in allowlist`. Refused by a restriction on the policy: `403 policy_violation` with the message `model "<model>" is blocked by policy`. Outside the key’s provider access: `400 model_not_allowed`. A path with no `/models/{model}` segment answers `400 missing_model`.
Body	Forwarded as written. No parameter policy applies, and `drop_tuning_params` is not read.
Query string	Forwarded as written.
`Authorization`, `x-api-key`, `x-goog-api-key`	Removed. The gateway adds the provider’s own key.
Hop-by-hop headers (`Connection`, `Transfer-Encoding`, `Upgrade`, and the rest)	Removed.
Every other header	Forwarded as written.

The X-LangWatch-End-User-Id, X-LangWatch-Metadata and Traceparent request headers work as on Chat Completions.

Response headers

Google’s own response headers, including its Content-Type, plus the gateway set from Chat Completions: X-LangWatch-Gateway-Version, X-LangWatch-Gateway-Request-Id, X-LangWatch-Fallback-Count, X-LangWatch-Budget-Warning, Traceparent, X-LangWatch-Heartbeat-Active, and X-LangWatch-Provider on a forwarded provider error. X-LangWatch-Handled-Error carries the error.code when the gateway wrote the error itself, and is removed from a forwarded provider response.

Streaming

A path ending in :streamGenerateContent or :streamGenerateAnswer streams. Google’s own SSE frames reach the client exactly as Google framed them, with no data: [DONE] trailer and no re-wrapping. A failure after the stream opens adds one terminal event: error frame that the gateway writes itself. Pass the query string Google expects for SSE, for example ?alt=sse, as you would against Google directly.

curl "https://gateway.langwatch.ai/v1beta/models/gemini-2.5-flash:streamGenerateContent?alt=sse" \
  -H "x-goog-api-key: $LANGWATCH_VIRTUAL_KEY" \
  -H "Content-Type: application/json" \
  -d '{"contents": [{"role": "user", "parts": [{"text": "Hi"}]}]}'

A failure after the stream opened ends it with an event: error frame; see Errors.

Errors

Code	Status	Cause
`model_provider_not_bound`	400	The key has no Gemini and no Vertex credential.
`missing_model`	400	The path carries no `/models/{model}` segment.
`policy_violation`	403	The model is outside the routing policy (`is not in allowlist`) or refused by one of its restrictions (`is blocked by policy`). Same shape as on every other route. See Policy rules.
`model_not_allowed`	400	The model is outside the key’s allowlist or provider access.

Google’s own errors are forwarded with Google’s status, body and headers, under X-LangWatch-Provider. The full table is on Errors. Also check: Gemini, Vertex AI.

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Gemini native (/v1beta)

Endpoint

Request

Response

Which credentials serve it

What the gateway reads and changes

Response headers

Streaming

Errors

​Endpoint

​Request

​Response

​Which credentials serve it

​What the gateway reads and changes

​Response headers

​Streaming

​Errors

Endpoint

Request

Response

Which credentials serve it

What the gateway reads and changes

Response headers

Streaming

Errors