The Claude Opus 4.8 API handles our 500K-token legal corpus in one call — no chunking pipeline, no retrieval glue. Ship speed doubled.
The Claude Opus 4.8 API is Anthropic's most capable chat model — 1M-token context window, adaptive extended thinking, mid-conversation system-message injection, and prompt caching. The Claude Opus 4.8 API is OpenAI-compatible: point any existing SDK at RouterBase and swap the model name to start using it. Input at $5 / 1M tokens, output at $25 / 1M tokens, cache reads at $0.50 / 1M tokens — all through one REST endpoint.
Input
Claude Opus 4.8
Hi! I'm a helpful AI assistant. What can I do for you?
Claude Opus 4.8 API: Chat
Use the Claude Opus 4.8 API to run Anthropic's flagship reasoning model with a 1M-token context window.
The Claude Opus 4.8 API is Anthropic's most powerful chat model — 1-million-token context, adaptive extended thinking, mid-conversation system-message injection, and built-in prompt caching. It is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, swap the model name to claude-opus-4-8, and your first call goes through immediately.
Pricing is $5.00 / 1M input tokens, $25.00 / 1M output tokens, and $0.50 / 1M cached-input reads. One RouterBase key — no Anthropic-specific SDK or separate credentials required.
Six reasons teams ship on the Claude Opus 4.8 API
From extended reasoning to prompt caching — what makes Opus 4.8 stand out.
1M-token context
Accepts up to 1 million tokens per request — entire codebases, legal corpora, or long document chains fit in a single call without chunking or retrieval glue.
Adaptive extended thinking
Enable extended reasoning mode to let Opus 4.8 think through hard problems step-by-step before answering. The model allocates internal scratchpad compute to difficult sub-problems automatically — no prompt engineering required.
Mid-conversation system messages
Inject new system instructions between turns. Switch tone, add compliance constraints, or change persona without ending the session — unique to the Anthropic Opus family.
Prompt caching
Cache repeated prefixes with the Claude Opus 4.8 API. Cache reads cost $0.50 / 1M tokens — up to 90% savings on workloads with stable system prompts, few-shot examples, or reference documents.
OpenAI-compatible endpoint
The Claude Opus 4.8 API speaks the OpenAI chat-completions wire format. Any Python, Node, Go, or Rust SDK that works with OpenAI works here — just update the base URL and model name.
One key for 200+ models
The same RouterBase key that calls the Claude Opus 4.8 API also routes to GPT-5, Gemini 3.5 Flash, Sora 2, and 200+ other models — no per-provider credential management.
Quickstart
Get started with the Claude Opus 4.8 API in 3 steps
From sign-up to your first response in under 5 minutes.
Create a RouterBase API key
Sign up and generate an API key — one key reaches the Claude Opus 4.8 API and every other model in the catalog.
Send your first message
Point any OpenAI-compatible SDK at routerbase.com/v1 and set the model to claude-opus-4-8. The response follows the standard chat-completions schema — streaming supported.
Inspect usage
Every response includes a detailed token breakdown — input, output, and cache-read tokens — so cost and cache-hit rate are visible on every call.
Pay only for what you use
RouterBase passes through partner-tier pricing. Compared against the model's official published API rate.
What teams build with the Claude Opus 4.8 API
Real production loads running on the Claude Opus 4.8 API and the RouterBase model catalog.
We switched from GPT-4 to the Claude Opus 4.8 API with a two-line change. Zero regression on our eval suite.
Prompt caching cut our monthly bill by 78% — the system prompt is 40K tokens and hits the cache every time. RouterBase made the switch painless.
Extended thinking solved planning tasks our previous model couldn't touch. Accuracy up 34% on our internal benchmark — all via the Claude Opus 4.8 API.
One million tokens of context means I can throw the whole repo at it. No more 'context limit exceeded' at 3 AM.
RouterBase puts the Claude Opus 4.8 API and 200+ other models behind one key. Our team stopped filing requests for new provider accounts.
Mid-conversation system messages let us hot-swap compliance constraints between turns — no session restart, no lost history.
We migrated 42 services to the Claude Opus 4.8 API over a weekend. The only PR comment was 'wait, that's all?'.
At our token volume, cache-read pricing saves us six figures per quarter. The ROI math was instant the moment we saw the Claude Opus 4.8 API pricing page.
Frequently Asked Questions
Common questions about the Claude Opus 4.8 API.
It is RouterBase's pass-through to Anthropic's Opus 4.8 model — a 1M-token context chat endpoint with adaptive extended thinking, mid-conversation system messages, and prompt caching, served via an OpenAI-compatible REST interface.