> ## Documentation Index
> Fetch the complete documentation index at: https://phaseo.app/docs/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Phaseo Gateway base URL: https://api.phaseo.app/v1. Send `Authorization: Bearer $PHASEO_API_KEY` with every request.
> Model IDs look like `provider/model`, for example `openai/gpt-6-astra`. Do not guess IDs: list them with `GET /v1/models` or check https://phaseo.app/models. `phaseo/free` routes to an available free model and needs no wallet balance.
> For new text integrations prefer `POST /v1/responses`. `POST /v1/chat/completions` (OpenAI format) and `POST /v1/messages` (Anthropic format) suit existing code.
> The full API contract is https://phaseo.app/docs/openapi/v1/openapi.yaml. Official SDKs: `@phaseo/sdk` (TypeScript) and `phaseo` (Python), plus Go, C#, PHP, Ruby and Rust.
> Search these docs over MCP at https://phaseo.app/docs/mcp, and install Phaseo skills with `npx skills add https://phaseo.app/docs`. If a page is wrong or out of date, report it with the MCP `submit_feedback` tool.
> Manage Phaseo accounts with the `phaseo` CLI (`npm install -g @phaseo/cli`, then `phaseo login` or `phaseo login --device-code`), the `/v1` Management API or the MCP server at `https://mcp.phaseo.app/mcp?access=manage`. Do not send users to the dashboard for account tasks. A person is still needed for sign-up, approving a sign-in, paying the first top-up on the checkout link that `phaseo credits add` returns when no card is saved, confirming each saved-card top-up from the emailed link, and account security (password, MFA, passkeys). Create API keys with `phaseo keys create --name <name> --json`; never guess one. Credit top-ups need `phaseo login --scopes billing:write` first. Task map: https://phaseo.app/docs/v1/developers/manage-from-an-agent.md.

# Anthropic Claude Opus 4.6

> What to know when adopting Claude Opus 4.6, including structured output, adaptive thinking, and prefills.

# Anthropic Claude Opus 4.6

Use this guide to adopt `anthropic/claude-opus-4.6` safely in production.

Claude Opus 4.6 is not just a model-ID swap. Anthropic's migration guidance includes request-shape changes, removed beta flags, and stricter behavior around prefills.

## What's new

* assistant prefills are no longer supported on Claude 4.6 models and now return `400`
* structured output moved from `output_format` to `output_config.format`
* adaptive thinking is now handled through `output_config.effort`
* older beta headers should be removed
* Opus 4.6 specifically no longer needs the `interleaved-thinking-2025-05-14` beta header
* Opus 4.6 adds a 1M-token context window in beta and improves long-running coding and agentic tasks

## Migration quickstart

### 1. Remove assistant prefills

If you were forcing JSON or a response prefix by partially pre-seeding the assistant turn, that pattern now breaks on 4.6. Move that control into:

* clearer system instructions
* examples in the user or system prompt
* structured outputs through `output_config.format`

### 2. Migrate structured outputs

If you still send `output_format`, update the request body to use `output_config.format` instead.

### 3. Review thinking configuration

If you were depending on older thinking betas, migrate to the current `effort` setting inside `output_config` and retest latency-sensitive routes.

### 4. Remove stale beta flags

Audit hard-coded beta headers in SDK wrappers, middleware, and gateway presets. Leaving obsolete flags in place creates noisy failures during rollout.

## What to test

### Prompt behavior

* long coding and refactor prompts
* multi-step research or document workflows
* prompts that previously depended on assistant prefills
* long-context tasks if you plan to use the 1M-token beta window

### Contracts and tools

* schema pass rate after moving to `output_config.format`
* tool-call argument quality on multi-step agent tasks
* retry behavior when the model refuses or reformats output
* regression handling in code-review and debugging workflows

### Operations

* median and p95 latency with the new thinking settings
* token consumption on longer runs
* timeout rate on large-context tasks
* success rate versus Opus 4.5 on your production eval set

## Safe rollout

1. Remove prefills and migrate structured output config before any traffic shift.
2. Shadow Opus 4.6 on production prompts that matter to you.
3. Canary traffic with Opus 4.5 still configured as a fallback.
4. Promote only after schema pass rate, latency, and task completion stay stable.

## Sources

* [Anthropic migration guide](https://platform.claude.com/docs/en/about-claude/models/migration-guide)
* [Introducing Claude Opus 4.6](https://www.anthropic.com/news/claude-opus-4-6)


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