Google Vertex AI Provider

Use Gemini models through Appam's Vertex client with streaming and function calling.

Setup

The Vertex client accepts either an API key or an OAuth bearer token.

export GOOGLE_VERTEX_API_KEY="..."
# or GOOGLE_API_KEY / GEMINI_API_KEY

# optional project-scoped routing
export GOOGLE_VERTEX_PROJECT="my-gcp-project"
export GOOGLE_VERTEX_LOCATION="us-central1"

Optional config-only tuning:

export GOOGLE_VERTEX_MODEL="gemini-2.5-flash"
export GOOGLE_VERTEX_INCLUDE_THOUGHTS=true
export GOOGLE_VERTEX_THINKING_LEVEL=HIGH

Quick Start

Vertex is auto-detected from vertex/..., gemini-..., and google/gemini... model strings:

use appam::prelude::*;

#[tokio::main]
async fn main() -> Result<()> {
    let agent = Agent::quick(
        "gemini-2.5-flash",
        "You are a helpful assistant.",
        vec![],
    )?;

    agent
        .stream("Explain quantum entanglement.")
        .on_content(|text| print!("{}", text))
        .run()
        .await?;

    Ok(())
}

Explicit Builder Form

use appam::prelude::*;

let agent = AgentBuilder::new("vertex-agent")
    .provider(LlmProvider::Vertex)
    .model("gemini-2.5-pro")
    .system_prompt("You are a helpful assistant.")
    .build()?;

You can also override the API key directly:

let agent = AgentBuilder::new("vertex-agent")
    .provider(LlmProvider::Vertex)
    .vertex_api_key("...")
    .model("gemini-2.5-flash")
    .system_prompt("You are a helpful assistant.")
    .build()?;

Function Calling

Tools registered with Appam are converted into Vertex function declarations automatically. The lower-level VertexConfig also exposes:

function_calling_mode
allowed_function_names
stream_function_call_arguments

Those settings live on VertexConfig, not on dedicated AgentBuilder methods.

Thinking Controls

Vertex thinking hints are currently configured through VertexConfig or the corresponding environment variables:

GOOGLE_VERTEX_INCLUDE_THOUGHTS
GOOGLE_VERTEX_THINKING_LEVEL

There is no Vertex-specific .thinking(...) builder method on AgentBuilder.

Example Binary

cargo run --example coding-agent-vertex