v2.0.0

---

title: 'v2.0.0'

What's New

v2.0 is a ground-up rework focused on performance, type safety, and a tighter API surface.

• Faster, leaner — streaming is more memory efficient, execution is lazy by default,
  and internal code paths have been consolidated.
• Tighter APIs — both Instructor and Polyglot have cleaner, more type-safe public APIs
  with explicit fields instead of mode-based configuration.
• More reliable — extensive unit, feature, integration tests and benchmarks back this
  release. A substantial number of bugs have been fixed across the stack.
• Agent building blocks — new cognesy/agents package for custom agents, and an expanded
  cognesy/agent-ctrl to interact with CLI coding agents from PHP.

Breaking Changes

• Instructor's public API centers on StructuredOutput, StructuredOutputRuntime,
  PendingStructuredOutput, StructuredOutputResponse, and StructuredOutputStream.
• Polyglot uses explicit LLM API fields (responseFormat, tools, toolChoice) instead
  of output modes. Streaming moves to stream()->deltas().

Instructor

• Execution flows through StructuredOutputRuntime, with lazy execution via PendingStructuredOutput.
• Streaming is Instructor-owned: StructuredOutputStream exposes responses(), partials(),
  and sequence(). StructuredOutputStreamState accumulates state internally.
• Configuration, validation, transformation, deserialization, and extraction are explicit
  parts of the runtime rather than scattered across older code paths.

Polyglot

• InferenceRuntime and EmbeddingsRuntime sit behind the Inference and Embeddings facades.
• New inference drivers: openai-responses, openresponses, glm, qwen.
• Built-in pricing via Pricing\Cost, per-model pricing objects, and cost calculators.
• Polyglot handles raw transport — structured value ownership belongs to Instructor.

Agents (cognesy/agents)

New package. Building blocks for custom agents: AgentLoop, AgentBuilder, hooks, guards,
templates, subagents, skills, and SessionRuntime for persisted workflows.

Compose agents from capabilities like bash, file tools, structured outputs, summarization,
self-critique, planning, execution history, and broadcasting.

Two built-in drivers: ToolCallingDriver (native tool-calling APIs) and ReActDriver
(Thought/Action/Observation loops).

AgentCtrl (cognesy/agent-ctrl)

Unified PHP API for interacting with CLI coding agents — Claude Code, Codex, OpenCode,
Pi (new), and Gemini (new).

• AgentCtrl::make() and dedicated builders (::codex(), ::openCode(), ::pi(),
  ::gemini()) return normalized AgentResponse objects.
• Streaming callbacks, session resume/continue, typed IDs (AgentSessionId,
  AgentToolCallId), and AgentCtrlConsoleLogger for observability.

Migrating from v1.x

• Instructor: use ->get(), ->response(), and ->stream(). For partial snapshots,
  switch to stream()->responses(), stream()->partials(), or stream()->sequence().
• Polyglot: replace mode-based JSON/tool config with responseFormat, tools,
  toolChoice, and delta-based streaming.
• See packages/instructor/docs/upgrade.md and packages/polyglot/docs/upgrade.md for details.