# Implementation Plan: [FEATURE]

**Branch**: `[###-feature-name]` | **Date**: [DATE] | **Spec**: [link]
**Input**: Feature specification from `/specs/[###-feature-name]/spec.md`

**Note**: This template is filled in by the `/speckit.plan` command. See `.specify/templates/commands/plan.md` for the execution workflow.

## Summary

Primary Requirement: Create a unified Python library to interface with multiple LLM providers (OpenAI, Anthropic, etc.) using a consistent, OpenAI-compatible API.
Technical Approach: Use the Bridge Pattern (`Client` -> `ProviderAdapter`) with `httpx` for requests. Support both Sync and Async execution. Enforce strictly typed configuration via dataclasses.

## Technical Context

**Language/Version**: Python >= 3.10
**Primary Dependencies**: httpx, pydantic (optional, using dataclasses primarily)
**Storage**: N/A
**Testing**: pytest
**Target Platform**: Cross-platform (Linux/macOS/Windows)
**Project Type**: single (Python Library)
**Performance Goals**: Minimal overhead (<5ms per streaming chunk)
**Constraints**: Interface must mirror OpenAI Python SDK; strict type hinting.
**Scale/Scope**: ~2000 LOC, Extensible provider system.

## Constitution Check

*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*

- [x] **Interface First**: Design mimics OpenAI SDK.
- [x] **Extensible**: Bridge pattern allows new providers.
- [x] **Low Coupling**: Business logic decoupled from provider implementation.
- [x] **Testable**: Independent testing strategy defined.

## Project Structure

### Documentation (this feature)

```text
specs/001-unified-api-router/
├── plan.md              # This file (/speckit.plan command output)
├── research.md          # Phase 0 output (/speckit.plan command)
├── data-model.md        # Phase 1 output (/speckit.plan command)
├── quickstart.md        # Phase 1 output (/speckit.plan command)
├── contracts/           # Phase 1 output (/speckit.plan command)
└── tasks.md             # Phase 2 output (/speckit.tasks command - NOT created by /speckit.plan)
```

### Source Code (repository root)

```text
src/
└── llm_api_router/
    ├── __init__.py
    ├── client.py        # Main Client & AsyncClient
    ├── types.py         # UnifiedRequest, UnifiedResponse, etc.
    ├── exceptions.py    # Unified Exception hierarchy
    └── providers/
        ├── __init__.py
        ├── base.py      # Abstract ProviderAdapter
        └── openai.py    # OpenAI Implementation

tests/
├── unit/
│   ├── test_client.py
│   └── test_providers/
└── integration/
    └── test_live_api.py
```

**Structure Decision**: Standard Python library structure using `src` layout.

## Complexity Tracking

> **Fill ONLY if Constitution Check has violations that must be justified**

| Violation | Why Needed | Simpler Alternative Rejected Because |
|-----------|------------|-------------------------------------|
| [e.g., 4th project] | [current need] | [why 3 projects insufficient] |
| [e.g., Repository pattern] | [specific problem] | [why direct DB access insufficient] |
