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Catalyst can proxy Vertex AI in two modes:
  • OpenAI-compatible Vertex endpoint: use the OpenAI SDK and set x-inference-provider-url to your Vertex /endpoints/openapi URL.
  • Native Vertex APIs: call the Vertex model operation path through the Catalyst gateway and set x-inference-provider-url to the global or regional aiplatform.googleapis.com base URL.
Use x-inference-provider: vertex-ai for both modes so Catalyst applies Vertex-specific URL and authentication handling.
This guide is for Gemini and Anthropic through Google Cloud Vertex AI. For direct Gemini API calls using generativelanguage.googleapis.com, see the Google Gemini guide.

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Supported Vertex endpoints

API shapeCatalyst path exampleStreaming
OpenAI-compatible Gemini/v1/chat/completions with x-inference-provider-url: .../endpoints/openapiYes
Native Gemini/v1/projects/{project}/locations/{location}/publishers/google/models/{model}:generateContentNo
Native Gemini stream/v1/projects/{project}/locations/{location}/publishers/google/models/{model}:streamGenerateContentYes
Anthropic on Vertex/v1/projects/{project}/locations/{location}/publishers/anthropic/models/{model}:rawPredictNo
Anthropic on Vertex stream/v1/projects/{project}/locations/{location}/publishers/anthropic/models/{model}:streamRawPredictYes
Native Gemini with API key/v1/publishers/google/models/{model}:generateContent with x-inference-provider-api-key: $GEMINI_VERTEX_API_KEYNo

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Environment

export INFERENCE_API_KEY="<your-catalyst-project-api-key>"
export GOOGLE_CLOUD_PROJECT="<your-gcp-project-id>"
export VERTEX_LOCATION="global"

# For OpenAI-compatible Vertex and Anthropic-on-Vertex.
export VERTEX_AI_ACCESS_TOKEN="$(gcloud auth print-access-token)"

# Optional for native Gemini on Vertex. Google API keys are forwarded as ?key=...
export GEMINI_VERTEX_API_KEY="<your-google-api-key>"
For regional Vertex endpoints, use the regional host: 
export VERTEX_BASE_URL="https://${VERTEX_LOCATION}-aiplatform.googleapis.com"
For the global location, use: 
export VERTEX_BASE_URL="https://aiplatform.googleapis.com"

​
OpenAI-compatible Vertex

Use this path when you want to keep the OpenAI SDK shape for Vertex Gemini models. 
import OpenAI from "openai";

const projectId = process.env.GOOGLE_CLOUD_PROJECT!;
const location = process.env.VERTEX_LOCATION ?? "global";
const vertexHost =
  location === "global"
    ? "https://aiplatform.googleapis.com"
    : `https://${location}-aiplatform.googleapis.com`;

const client = new OpenAI({
  baseURL: "https://api.inference.net/v1",
  apiKey: process.env.INFERENCE_API_KEY,
  defaultHeaders: {
    "x-inference-provider": "vertex-ai",
    "x-inference-provider-api-key": process.env.VERTEX_AI_ACCESS_TOKEN!,
    "x-inference-provider-url": `${vertexHost}/v1/projects/${projectId}/locations/${location}/endpoints/openapi`,
    "x-inference-environment": "production",
  },
});

const response = await client.chat.completions.create(
  {
    model: "google/gemini-2.0-flash-001",
    messages: [{ role: "user", content: "Reply with exactly OK." }],
    max_tokens: 32,
  },
  {
    headers: { "x-inference-task-id": "vertex-openai-compatible" },
  },
);

import os
from openai import OpenAI

project_id = os.environ["GOOGLE_CLOUD_PROJECT"]
location = os.getenv("VERTEX_LOCATION", "global")
vertex_host = (
    "https://aiplatform.googleapis.com"
    if location == "global"
    else f"https://{location}-aiplatform.googleapis.com"
)

client = OpenAI(
    base_url="https://api.inference.net/v1",
    api_key=os.environ["INFERENCE_API_KEY"],
    default_headers={
        "x-inference-provider": "vertex-ai",
        "x-inference-provider-api-key": os.environ["VERTEX_AI_ACCESS_TOKEN"],
        "x-inference-provider-url": f"{vertex_host}/v1/projects/{project_id}/locations/{location}/endpoints/openapi",
        "x-inference-environment": "production",
    },
)

response = client.chat.completions.create(
    model="google/gemini-2.0-flash-001",
    messages=[{"role": "user", "content": "Reply with exactly OK."}],
    max_tokens=32,
    extra_headers={"x-inference-task-id": "vertex-openai-compatible"},
)

​
Native Gemini on Vertex

Use native Gemini paths when you need Vertex’s generateContent or streamGenerateContent request format. 
curl "https://api.inference.net/v1/projects/${GOOGLE_CLOUD_PROJECT}/locations/${VERTEX_LOCATION}/publishers/google/models/gemini-2.0-flash-001:generateContent" \
  -H "Authorization: Bearer ${INFERENCE_API_KEY}" \
  -H "Content-Type: application/json" \
  -H "x-inference-provider: vertex-ai" \
  -H "x-inference-provider-api-key: ${VERTEX_AI_ACCESS_TOKEN}" \
  -H "x-inference-provider-url: ${VERTEX_BASE_URL}" \
  -H "x-inference-environment: production" \
  -H "x-inference-task-id: vertex-native-gemini" \
  -d '{
    "contents": [
      {
        "role": "user",
        "parts": [{ "text": "Reply with exactly OK." }]
      }
    ],
    "generationConfig": { "maxOutputTokens": 64, "temperature": 0 }
  }'
If you are using a Google API key instead of an OAuth access token for Gemini, pass GEMINI_VERTEX_API_KEY as x-inference-provider-api-key. Catalyst forwards Google API keys to Vertex as the key query parameter. 
curl "https://api.inference.net/v1/publishers/google/models/gemini-2.0-flash-001:generateContent" \
  -H "Authorization: Bearer ${INFERENCE_API_KEY}" \
  -H "Content-Type: application/json" \
  -H "x-inference-provider: vertex-ai" \
  -H "x-inference-provider-api-key: ${GEMINI_VERTEX_API_KEY}" \
  -H "x-inference-provider-url: https://aiplatform.googleapis.com" \
  -H "x-inference-environment: production" \
  -H "x-inference-task-id: vertex-native-gemini-api-key" \
  -d '{
    "contents": [
      {
        "role": "user",
        "parts": [{ "text": "Reply with exactly OK." }]
      }
    ],
    "generationConfig": { "maxOutputTokens": 64, "temperature": 0 }
  }'
For Gemini streaming, use :streamGenerateContent. Add ?alt=sse if you want Vertex to return server-sent events. 
curl "https://api.inference.net/v1/projects/${GOOGLE_CLOUD_PROJECT}/locations/${VERTEX_LOCATION}/publishers/google/models/gemini-2.0-flash-001:streamGenerateContent?alt=sse" \
  -H "Authorization: Bearer ${INFERENCE_API_KEY}" \
  -H "Content-Type: application/json" \
  -H "x-inference-provider: vertex-ai" \
  -H "x-inference-provider-api-key: ${VERTEX_AI_ACCESS_TOKEN}" \
  -H "x-inference-provider-url: ${VERTEX_BASE_URL}" \
  -H "x-inference-environment: production" \
  -H "x-inference-task-id: vertex-native-gemini-stream" \
  -d '{
    "contents": [
      {
        "role": "user",
        "parts": [{ "text": "Reply with exactly OK." }]
      }
    ],
    "generationConfig": { "maxOutputTokens": 64, "temperature": 0 }
  }'

​
Anthropic on Vertex

Anthropic models on Vertex use Vertex operation paths and Anthropic’s Vertex payload shape. Use a Google Cloud OAuth access token or service-account-minted access token as x-inference-provider-api-key. 
curl "https://api.inference.net/v1/projects/${GOOGLE_CLOUD_PROJECT}/locations/${VERTEX_LOCATION}/publishers/anthropic/models/claude-sonnet-4-5:rawPredict" \
  -H "Authorization: Bearer ${INFERENCE_API_KEY}" \
  -H "Content-Type: application/json" \
  -H "x-inference-provider: vertex-ai" \
  -H "x-inference-provider-api-key: ${VERTEX_AI_ACCESS_TOKEN}" \
  -H "x-inference-provider-url: ${VERTEX_BASE_URL}" \
  -H "x-inference-environment: production" \
  -H "x-inference-task-id: vertex-anthropic" \
  -d '{
    "anthropic_version": "vertex-2023-10-16",
    "max_tokens": 512,
    "messages": [
      {
        "role": "user",
        "content": "Reply with exactly OK."
      }
    ]
  }'
For streaming Anthropic responses on Vertex, use :streamRawPredict and include "stream": true in the body. 
curl "https://api.inference.net/v1/projects/${GOOGLE_CLOUD_PROJECT}/locations/${VERTEX_LOCATION}/publishers/anthropic/models/claude-sonnet-4-5:streamRawPredict" \
  -H "Authorization: Bearer ${INFERENCE_API_KEY}" \
  -H "Content-Type: application/json" \
  -H "x-inference-provider: vertex-ai" \
  -H "x-inference-provider-api-key: ${VERTEX_AI_ACCESS_TOKEN}" \
  -H "x-inference-provider-url: ${VERTEX_BASE_URL}" \
  -H "x-inference-environment: production" \
  -H "x-inference-task-id: vertex-anthropic-stream" \
  -d '{
    "anthropic_version": "vertex-2023-10-16",
    "max_tokens": 512,
    "stream": true,
    "messages": [
      {
        "role": "user",
        "content": "Reply with exactly OK."
      }
    ]
  }'

​
Header summary

HeaderRequiredNotes
AuthorizationYesYour Catalyst project API key.
x-inference-providerYesSet to vertex-ai.
x-inference-provider-api-keyYesGoogle API key for native Gemini, or OAuth2 access token for Vertex.
x-inference-provider-urlYesVertex host or /endpoints/openapi URL, depending on the API shape.
x-inference-environmentNoDashboard environment tag.
x-inference-task-idNoDashboard task grouping.