> ## 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 If a page is wrong or out of date, report it with the MCP `submit_feedback` tool.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 5

> What to know when adopting Claude Opus 5 for long-context reasoning, coding, and agentic workloads.

# Anthropic Claude Opus 5

Use this guide to adopt `anthropic/claude-opus-5` safely in production.

Claude Opus 5 is the current Opus model for complex reasoning, long-horizon agentic coding, and high-autonomy workflows. It keeps the same price as Opus 4.8 while supporting a 1M-token context window and up to 128K output tokens.

## Migration quickstart

1. Change the model ID to `anthropic/claude-opus-5` without changing the rest of the request.
2. Re-run your production prompt, tool, and structured-output evaluations.
3. Rebaseline latency, token use, and task cost for long-context and high-effort workloads.
4. Canary the model behind a fallback to Claude Opus 4.8 before changing your default route.

```json theme={null}
{
  "model": "anthropic/claude-opus-5",
  "messages": [
    {
      "role": "user",
      "content": "Review this implementation plan and identify the highest-risk assumptions."
    }
  ]
}
```

## What's new

* the Phaseo model ID is `anthropic/claude-opus-5`
* the context window is 1M tokens
* the maximum output is 128K tokens
* the model is positioned for longer-running reasoning, coding, and autonomous tool workflows
* pricing remains aligned with Claude Opus 4.8

## What to test

### Prompts and outputs

* instruction following on your longest system prompts
* structured-output and schema pass rates
* response length and stopping behavior
* regressions in prompts tuned specifically for Claude Opus 4.8

### Tools and agents

* tool selection and argument quality
* recovery after tool errors or partial results
* long-horizon completion rate
* permission and approval boundaries in high-autonomy workflows

### Operations

* latency and token use at each effort level you expose
* context-window usage on long documents and agent traces
* cost per successful task
* fallback behavior when the primary route times out or fails

## Safe rollout

1. Keep Claude Opus 4.8 available as a fallback during evaluation.
2. Shadow representative production traffic before serving user requests.
3. Canary by workload rather than moving every Opus route at once.
4. Promote only after quality, latency, cost, and tool-safety checks meet your targets.

## Sources

* [Claude Opus 5 announcement](https://www.anthropic.com/news/claude-opus-5)
* [Claude Opus 5 system card](https://www.anthropic.com/claude-opus-5-system-card)


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