fabro/lib/crates/fabro-llm

fabro-llm

A unified async Rust client library for multiple LLM providers. Write your LLM integration code once and switch between Anthropic, OpenAI, and Google Gemini without changing your application logic.

Key concepts

• Client -- Routes requests to registered provider adapters. Build it from a CredentialSource or explicit typed credentials.
• ProviderAdapter -- The trait every provider implements (complete and stream). Built-in adapters: AnthropicAdapter, OpenAiAdapter, GeminiAdapter, OpenAiCompatibleAdapter.
• Middleware -- Intercepts requests/responses for logging, caching, or transformation. Supports both blocking and streaming paths.
• generate() -- High-level function that wraps Client.complete() with automatic tool execution loops, retries, timeouts, and cancellation.
• Tool -- Active tools (with an execute handler) run automatically in the tool loop. Passive tools (no handler) surface tool calls back to the caller.
• Model catalog -- Built-in metadata for common models. Advisory only; unknown model strings pass through.

Providers

Provider	Adapter	API	Env var
Anthropic	AnthropicAdapter	Messages API	ANTHROPIC_API_KEY
OpenAI	OpenAiAdapter	Responses API	OPENAI_API_KEY
Google Gemini	GeminiAdapter	generateContent	GEMINI_API_KEY or GOOGLE_API_KEY
OpenAI-compatible	OpenAiCompatibleAdapter	Chat Completions	(custom)

All adapters support streaming, tool calling, structured output (response_format), and provider-specific options via provider_options.

Usage

Create from an environment-backed credential source

use fabro_auth::EnvCredentialSource;
use fabro_llm::client::Client;
use fabro_llm::types::{Message, Request};

let source = EnvCredentialSource::new();
let client = Client::from_source(&source).await?;

let request = Request {
    model: "claude-sonnet-4-5".to_string(),
    messages: vec![Message::user("What is the capital of France?")],
    provider: None,
    tools: None,
    tool_choice: None,
    response_format: None,
    temperature: Some(0.0),
    top_p: None,
    max_tokens: Some(100),
    stop_sequences: None,
    reasoning_effort: None,
    metadata: None,
    provider_options: None,
};

let response = client.complete(&request).await?;
println!("{}", response.text());

High-level generate()

use fabro_auth::EnvCredentialSource;
use fabro_llm::client::Client;
use fabro_llm::generate::{generate, GenerateParams};

let source = EnvCredentialSource::new();
let client = Client::from_source(&source).await?;
let result = generate(
    GenerateParams::new("claude-sonnet-4-5", client.clone())
        .prompt("Explain monads in one sentence")
        .system("You are a concise programming tutor.")
        .max_tokens(200)
).await?;

println!("{}", result.text());

Tool calling

use fabro_auth::EnvCredentialSource;
use fabro_llm::client::Client;
use fabro_llm::generate::{generate, GenerateParams};
use fabro_llm::tools::Tool;
use std::sync::Arc;

let source = EnvCredentialSource::new();
let client = Client::from_source(&source).await?;
let weather_tool = Tool::active(
    "get_weather",
    "Get the current weather for a city",
    serde_json::json!({
        "type": "object",
        "properties": {
            "city": {"type": "string", "description": "City name"}
        },
        "required": ["city"]
    }),
    |args, _ctx| async move {
        let city = args["city"].as_str().unwrap_or("unknown");
        Ok(serde_json::json!({"temp": "72F", "city": city}))
    },
);

let result = generate(
    GenerateParams::new("claude-sonnet-4-5", client.clone())
        .prompt("What's the weather in San Francisco?")
        .tools(vec![weather_tool])
        .max_tool_rounds(3)
).await?;

Streaming

use fabro_auth::EnvCredentialSource;
use fabro_llm::client::Client;
use fabro_llm::types::{Message, Request, StreamEvent};
use futures::StreamExt;

let source = EnvCredentialSource::new();
let client = Client::from_source(&source).await?;
let request = Request {
    model: "claude-sonnet-4-5".to_string(),
    messages: vec![Message::user("Tell me a joke")],
    // ...other fields set to None/defaults
    # provider: None, tools: None, tool_choice: None,
    # response_format: None, temperature: None, top_p: None,
    # max_tokens: None, stop_sequences: None, reasoning_effort: None,
    # metadata: None, provider_options: None,
};

let mut stream = client.stream(&request).await?;
while let Some(event) = stream.next().await {
    match event? {
        StreamEvent::TextDelta { delta, .. } => print!("{delta}"),
        StreamEvent::Finish { response, .. } => {
            println!("\nTokens used: {}", response.usage.total_tokens);
        }
        _ => {}
    }
}

Middleware

use fabro_llm::error::Error;
use fabro_llm::middleware::{Middleware, NextFn, NextStreamFn};
use fabro_llm::provider::StreamEventStream;
use fabro_llm::types::{Request, Response};

struct LoggingMiddleware;

#[async_trait::async_trait]
impl Middleware for LoggingMiddleware {
    async fn handle_complete(
        &self,
        request: Request,
        next: NextFn,
    ) -> Result<Response, Error> {
        eprintln!("Request to model: {}", request.model);
        let response = next(request).await?;
        eprintln!("Response tokens: {}", response.usage.total_tokens);
        Ok(response)
    }

    async fn handle_stream(
        &self,
        request: Request,
        next: NextStreamFn,
    ) -> Result<StreamEventStream, Error> {
        next(request).await
    }
}

OpenAI-compatible providers

use fabro_llm::providers::OpenAiCompatibleAdapter;
use std::sync::Arc;

let adapter = OpenAiCompatibleAdapter::new("your-api-key", "https://api.groq.com/openai/v1")
    .with_name("groq");

Model catalog

use fabro_llm::catalog::{get_latest_model, get_model_info, list_models};

let info = get_model_info("claude-opus-4-6");
let anthropic_models = list_models(Some("anthropic"));
let best_reasoner = get_latest_model("anthropic", Some("reasoning"));

Key types

Type	Description
Request	Unified request with model, messages, tools, temperature, etc.
Response	Unified response with message, finish reason, usage, rate limit info
Message	A message with role, content parts, and optional tool call ID
ContentPart	Text, Image, Audio, Document, ToolCall, ToolResult, Thinking
StreamEvent	Events for streaming: TextDelta, ToolCallStart/Delta/End, Finish, etc.
SdkError	Typed errors with retryability, status codes, and provider error kinds
GenerateParams	Builder for the high-level generate() function
GenerateResult	Result containing response, tool results, total usage, and step history
ToolDefinition	Tool name, description, and JSON Schema parameters
ToolChoice	Auto, None, Required, or Named tool selection
Usage	Token counts including input, output, reasoning, and cache tokens
RetryPolicy	Configurable retry with exponential backoff, jitter, and max delay
Model	Metadata about a model (context window, capabilities, costs)

Error handling

SdkError provides structured error variants with built-in retryability classification:

• Retryable: RateLimit, Server, Network, Stream, RequestTimeout
• Non-retryable: Authentication, AccessDenied, InvalidRequest, ContextLength, Configuration

The retry() function and generate() respect Retry-After headers and use exponential backoff with jitter.

Provider-specific options

Pass provider-specific parameters via provider_options without losing portability:

use fabro_llm::types::Request;

let request = Request {
    provider_options: Some(serde_json::json!({
        "anthropic": {
            "thinking": {"type": "enabled", "budget_tokens": 10000},
            "auto_cache": true
        },
        "openai": {
            "store": true,
            "previous_response_id": "resp_abc123"
        },
        "gemini": {
            "safetySettings": [
                {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_NONE"}
            ]
        }
    })),
    // ...other fields
    # model: String::new(), messages: vec![], provider: None, tools: None,
    # tool_choice: None, response_format: None, temperature: None,
    # top_p: None, max_tokens: None, stop_sequences: None,
    # reasoning_effort: None, metadata: None,
};