Agent SDK overview

Use a Phaseo Agent SDK when one request isn’t enough: the SDK runs a bounded loop in your process that sends each turn to the Responses API, runs the tools the model calls, and pauses for a person when a tool needs approval. You keep the run state; Phaseo hosts nothing for the agent.

Pick your package

Language	Package	Version	Core client it installs
TypeScript	`@phaseo/agent-sdk`	0.3.0	`@phaseo/sdk`
Python	`phaseo-agent-sdk` (module `phaseo_agent`)	0.3.0	`phaseo` 3.x
Go	`github.com/phaseoteam/Phaseo/packages/sdk/agent-sdk-go`	v0.3.0	`sdk-go/v3`
C#	`Phaseo.AgentSdk`	0.3.0	`Phaseo.Sdk`
PHP	`phaseo/agent-sdk`	v0.3.0	`phaseo/sdk` `^3.0.0`
Ruby	`phaseo_agent_sdk`	0.3.0	`phaseo_sdk` `>= 3.0.0, < 4.0.0`
Java	`app.phaseo:phaseo-agent-sdk` (Maven Central)	0.3.0	`app.phaseo:phaseo-sdk` 3.0.0
Rust	`phaseo-agent`	0.2.0	`phaseo` 0.2

TypeScript is the reference design. C++ has no Agent SDK. Installation has the install commands and runtime requirements, and Usage builds a first agent.

Ask a coding agent to build a first agent with the Phaseo Agent SDK in your language.

Open in Cursor

Compare what each runtime supports

Every SDK runs local tools, pauses on exact tool-call IDs for approval or manual output, and returns serializable run state your application stores. The rest differs by language:

Capability	TypeScript	Python	Go	C#	PHP	Ruby	Java	Rust
Default step limit	12	12	8	12	12	12	12	8
Step limit reached	Throws `Max steps exceeded`	Raises `RuntimeError`	Returns an error	Throws `InvalidOperationException`	Throws	Raises	Throws	Returns a `stopped` run (`max_steps:N`)
Model streaming	Async iterable	Iterator (background thread)	Channel	Async enumerable	Iterable; runs only while you iterate (Fiber)	Enumerator (worker thread)	Lists after the run; live through `onEvent`	Not yet
Tool progress events	Async generator	`emit_progress` or generator	`EmitProgress`	`EmitProgress`	`emitProgress`	`emit_progress`	`emitProgress`	Not yet
Concurrent tools	Yes	Yes (threads)	Yes	Yes	No	Yes (threads)	Yes (thread pool)	No
Tool timeout	Aborts `context.signal`	Fails the run; thread keeps running	Fails the call; goroutine keeps running	Cancels `CancellationToken`	Checked after the tool returns	Interrupts the call	Interrupts the thread	None
Runtime schema validation	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No; JSON Schema is only sent to the model
Tool error by default	Fails the run	Fails the run	Fails the run	Fails the run	Fails the run	Fails the run	Fails the run	Returned to the model
Approve and reject by call ID	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Approve only
Interactive (human-in-the-loop) tools	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Agent-level `human_review` only
Stop conditions	Composable	Composable; checked only on steps without tool calls	Composable	Composable	Composable	Composable	Composable	Step limit
Dynamic turns	Yes	Model, instructions, and sampling; tools through `next_turn_params`	Yes	Yes	Yes	Yes	Yes	Per-run model, step limit, and context
Typed timeline items	`AgentItem` union	Dicts	`Details` map	`Details` dictionary	Arrays	Hashes	`details()` map	No; read `messages` and `steps`
Usage and cost	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Tokens, plus cost when the response has `meta.cost` or `cost`
Cancellation	`cancel()`	`cancel()`	Context	`CancellationToken`	`cancel()`	`cancel`	`cancel()`	Not yet
Devtools capture	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Not yet

Rust (phaseo-agent 0.2) is synchronous: no streaming, async execution, concurrent tools, runtime schema validation, or Devtools capture. Run it on a worker thread when a run shouldn’t block a request handler. PHP runs tools one at a time, and its stream only advances while your code iterates.

Choose the Agent SDK, the client, or the raw 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

Each Agent SDK’s gateway client sends model turns through that language’s client SDK. Most accept a requestOptions map (or the language’s equivalent) for extra Responses API fields; the agent still sets model, input, instructions, and its function tools. The Rust 0.2 adapter sends only the normalized agent fields and has no extra-options hook.

Start from a recipe

Recipe	Language
Build a durable agent loop	TypeScript
Research with structured output and web search	TypeScript
Support triage with presets and guardrail-aware failures	TypeScript
Run a coding-review agent with runtime tools	TypeScript
Fan out local agent tools concurrently	TypeScript
Extract structured JSON	Python
Build an ops runbook agent	Go
Triage tickets	C#
Review CMS content	PHP
Summarize internal notes	Ruby

The TypeScript recipes port to any language with the APIs on these pages.

Start Here

Build

Observe

Reference

Pick your package

Compare what each runtime supports

Choose the Agent SDK, the client, or the raw API

Start from a recipe

​Pick your package

​Compare what each runtime supports

​Choose the Agent SDK, the client, or the raw API

​Start from a recipe

Pick your package

Compare what each runtime supports

Choose the Agent SDK, the client, or the raw API

Start from a recipe