blazen 0.1.121

Features

• Event-driven architecture -- Type-safe events connect workflow steps with zero boilerplate via derive macros (Rust) or subclassing (Python) or plain objects (TypeScript)
• 15+ LLM providers -- OpenAI, Anthropic, Gemini, Azure, OpenRouter, Groq, Together AI, Mistral, DeepSeek, Fireworks, Perplexity, xAI, Cohere, AWS Bedrock, and fal.ai -- with streaming, tool calling, structured output, and multimodal support
• Multi-workflow pipelines -- Orchestrate sequential and parallel stages with pause/resume and per-workflow streaming
• Branching and fan-out -- Conditional branching, parallel fan-out, and real-time streaming within workflows
• Native Python and TypeScript bindings -- Python via PyO3/maturin, Node.js/TypeScript via napi-rs. Not wrappers around HTTP -- actual compiled Rust running in-process
• WebAssembly SDK -- Run Blazen in the browser, edge workers, Deno, and embedded runtimes via @blazen/sdk. Same Rust core compiled to WASM
• Prompt management -- Versioned prompt templates with {{variable}} interpolation, YAML/JSON registries, and multimodal attachments
• Persistence -- Embedded persistence via redb, or bring-your-own via callbacks. Pause a workflow, serialize state to JSON, resume later
• Identity-preserving live state -- Pass DB connections, Pydantic models, and other live objects through events and the new ctx.state / ctx.session namespaces. StopEvent(result=obj) round-trips non-JSON Python values with is-identity preserved -- the engine no longer silently stringifies unpicklable results
• Observability -- OpenTelemetry, Prometheus metrics, and Langfuse integration via the telemetry crate

Installation

Rust:

cargo add blazen

Python (requires Python 3.9+):

uv add blazen       # recommended
pip install blazen   # also works

Node.js / TypeScript:

pnpm add blazen

WebAssembly (browser, edge, Deno, Cloudflare Workers):

npm install @blazen/sdk

Quick Start

Rust

use blazen::prelude::*;

#[derive(Debug, Clone, Serialize, Deserialize, Event)]
struct GreetEvent {
    name: String,
}

#[step]
async fn parse_input(event: StartEvent, _ctx: Context) -> Result<GreetEvent, WorkflowError> {
    let name = event.data["name"].as_str().unwrap_or("World").to_string();
    Ok(GreetEvent { name })
}

#[step]
async fn greet(event: GreetEvent, _ctx: Context) -> Result<StopEvent, WorkflowError> {
    Ok(StopEvent {
        result: serde_json::json!({ "greeting": format!("Hello, {}!", event.name) }),
    })
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let workflow = WorkflowBuilder::new("greeter")
        .step(parse_input_registration())
        .step(greet_registration())
        .build()?;

    let handler = workflow.run(serde_json::json!({ "name": "Zach" })).await?;
    let result = handler.result().await?;

    if let Some(stop) = result.downcast_ref::<StopEvent>() {
        println!("{}", stop.result); // {"greeting": "Hello, Zach!"}
    }
    Ok(())
}

Python

from blazen import Workflow, step, Event, StartEvent, StopEvent, Context

class GreetEvent(Event):
    name: str

@step
async def parse_input(ctx: Context, ev: StartEvent) -> GreetEvent:
    return GreetEvent(name=ev.name or "World")

@step
async def greet(ctx: Context, ev: GreetEvent) -> StopEvent:
    return StopEvent(result={"greeting": f"Hello, {ev.name}!"})

async def main():
    wf = Workflow("greeter", [parse_input, greet])
    handler = await wf.run(name="Zach")
    result = await handler.result()
    print(result.to_dict())  # {"result": {"greeting": "Hello, Zach!"}}

import asyncio
asyncio.run(main())

TypeScript

import { Workflow } from "blazen";

const workflow = new Workflow("greeter");

workflow.addStep("parse_input", ["blazen::StartEvent"], async (event, ctx) => {
  const name = event.name ?? "World";
  return { type: "GreetEvent", name };
});

workflow.addStep("greet", ["GreetEvent"], async (event, ctx) => {
  return {
    type: "blazen::StopEvent",
    result: { greeting: `Hello, ${event.name}!` },
  };
});

const result = await workflow.run({ name: "Zach" });
console.log(result.data); // { greeting: "Hello, Zach!" }

LLM Integration

Every provider implements the same CompletionModel trait/interface. Switch providers by changing one line.

Rust

use blazen_llm::{CompletionModel, CompletionRequest, ChatMessage};
use blazen_llm::providers::openai::OpenAiProvider;

let model = OpenAiProvider::new("sk-...");
let request = CompletionRequest::new(vec![
    ChatMessage::user("What is the meaning of life?"),
]);
let response = model.complete(request).await?;
println!("{}", response.content.unwrap_or_default());

Use any OpenAI-compatible provider with OpenAiCompatProvider:

use blazen_llm::providers::openai_compat::OpenAiCompatProvider;

let groq = OpenAiCompatProvider::groq("gsk-...");
let openrouter = OpenAiCompatProvider::openrouter("sk-or-...");
let together = OpenAiCompatProvider::together("...");
let deepseek = OpenAiCompatProvider::deepseek("...");

Python

from blazen import CompletionModel, ChatMessage, Role, CompletionResponse

model = CompletionModel.openai("sk-...")
# or: CompletionModel.anthropic("sk-ant-...")
# or: CompletionModel.groq("gsk-...")
# or: CompletionModel.openrouter("sk-or-...")

response: CompletionResponse = await model.complete([
    ChatMessage.system("You are helpful."),
    ChatMessage.user("What is the meaning of life?"),
])
print(response.content)        # typed attribute access
print(response.model)          # model name used
print(response.usage)          # TokenUsage with .prompt_tokens, .completion_tokens, .total_tokens
print(response.finish_reason)

TypeScript

import { CompletionModel, ChatMessage, Role } from "blazen";
import type { CompletionResponse } from "blazen";

const model = CompletionModel.openai("sk-...");
// or: CompletionModel.anthropic("sk-ant-...")
// or: CompletionModel.groq("gsk-...")
// or: CompletionModel.openrouter("sk-or-...")

const response: CompletionResponse = await model.complete([
  ChatMessage.system("You are helpful."),
  ChatMessage.user("What is the meaning of life?"),
]);
console.log(response.content);      // string
console.log(response.model);        // model name used
console.log(response.usage);        // { promptTokens, completionTokens, totalTokens }
console.log(response.finishReason);

Streaming

Steps can publish intermediate events to an external stream via write_event_to_stream on the context. Consumers subscribe before awaiting the final result.

Rust

#[step]
async fn process(event: StartEvent, ctx: Context) -> Result<StopEvent, WorkflowError> {
    for i in 0..3 {
        ctx.write_event_to_stream(ProgressEvent { step: i }).await;
    }
    Ok(StopEvent { result: serde_json::json!({"done": true}) })
}

// Consumer side:
let handler = workflow.run(input).await?;
let mut stream = handler.stream_events();
while let Some(event) = stream.next().await {
    println!("got: {:?}", event.event_type_id());
}
let result = handler.result().await?;

Python

@step
async def process(ctx: Context, ev: StartEvent) -> StopEvent:
    for i in range(3):
        ctx.write_event_to_stream(Event("ProgressEvent", step=i))
    return StopEvent(result={"done": True})

# Consumer side:
handler = await wf.run(message="go")
async for event in handler.stream_events():
    print(event.event_type, event.to_dict())
result = await handler.result()

TypeScript

// Using runStreaming with a callback:
const result = await workflow.runStreaming({ message: "go" }, (event) => {
  console.log("stream:", event.type, event);
});

// Or using the handler API:
const handler = await workflow.runWithHandler({ message: "go" });
await handler.streamEvents((event) => {
  console.log("stream:", event.type, event);
});
const result = await handler.result();

Crate / Package Structure

Supported LLM Providers

All OpenAI-compatible providers are accessible through OpenAiCompatProvider in Rust, or through static factory methods on CompletionModel in Python and TypeScript.

Documentation

Full documentation, guides, and API reference are available at blazen.dev/docs/getting-started/introduction.

License

This project is licensed under the GNU Affero General Public License v3.0 (AGPL-3.0).

Author

Built by Zach Handley.