Agent SDK Overview - Phaseo Docs

Use the Phaseo Agent SDKs when your application needs more than one-shot generation:

multi-step tool loops
local runtime tools
gateway-backed model turns
resumable application-owned run state
exact-call approvals, human-in-the-loop tools, manual tools, and resumable continuation
runtime validation, progress-producing tools, and recoverable tool errors
streamed model output with replayable event consumers
dynamic turn configuration, composable stop conditions, and normalized usage/cost
model retries, tool timeouts, bounded tool concurrency, and lifecycle events
local Phaseo Devtools capture
consistent request routing across the same languages as the core client SDKs

Supported languages

The current Agent SDK language set matches the primary client SDK set exposed in Phaseo quickstart:

Common model

Each Agent SDK keeps the same runtime model:

define one agent
define zero or more local tools
create a gateway-backed model client
run a bounded loop over the responses API
inspect lifecycle events or a Devtools trace
persist the returned run and resume after a human decision

TypeScript is the reference API design. Python, Go, C#, PHP, and Ruby expose the broader cross-language contract using language-native callbacks, concurrency, timeout, and cancellation primitives. Rust is a supported synchronous runtime with local and external tools, exact-ID approvals, human review, model retries, serializable run state, lifecycle callbacks, and usage aggregation. Java and C++ remain work in progress.

The Rust Agent SDK is published as phaseo-agent. It does not yet include streaming, async execution, concurrent local tools, runtime schema validation, or Devtools capture.

Cross-language capability contract

Capability	TypeScript	Python	Go	C#	PHP	Ruby	Rust
Executable tools and recoverable tool errors	Yes	Yes	Yes	Yes	Yes	Yes	Synchronous
Exact-ID approvals, HITL, and manual outputs	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Preliminary tool progress	Async generator	Iterator or callback	Callback	Callback	Callback	Callback	Not yet
Model streaming and replayable consumers	Async iterable	Iterator	Channel	Async enumerable	Iterable	Enumerator	Not yet
Composable stop conditions	Yes	Yes	Yes	Yes	Yes	Yes	Step limit
Dynamic turns and mutable context	Yes	Yes	Yes	Yes	Yes	Yes	Per-run model, step limit, and context
Application-owned persisted run state	Yes	Yes	Yes	Yes	Yes	Yes	Serializable `RunResult`
Normalized usage and cost	Yes	Yes	Yes	Yes	Yes	Yes	Tokens; custom-client cost only in `0.1`

PHP and Ruby expose provider stream events through their normal synchronous iteration APIs. They do not require a hosted runtime or a background Phaseo service.

Client SDK, Agent SDK, and API

Use	Choose	What it owns
One API request or full endpoint coverage	Client SDK	Generated API types and transport
Tool-using, multi-step application logic	Agent SDK	Local loop, tools, checkpoints, review, events, and Devtools
Custom transport or an unsupported language	Raw API	HTTP request and response handling

Agent SDK gateway adapters delegate model turns to the matching Client SDK. Languages with a requestOptions or equivalent hook can pass additional Responses API fields through while the Agent SDK continues to own model, input, instructions, and local function tools. The Rust 0.1 adapter currently sends the normalized agent fields without an additional request-options hook.

Recipes

The cookbook includes TypeScript workflows and language-specific starting points:

​Supported languages

​Common model

​Cross-language capability contract

​Client SDK, Agent SDK, and API

​Recipes

Supported languages

Common model

Cross-language capability contract

Client SDK, Agent SDK, and API

Recipes