Claude Opus 5 API: Pricing, Context and Setup

Claude Opus 5 is Anthropic's current Opus-tier model, released on July 24, 2026. Its API model ID is claude-opus-5, its context window is 1 million tokens, and standard pricing is $5 per 1M input tokens and $25 per 1M output tokens — the same rate Anthropic charges for Claude Opus 4.8.

Claude Opus 5 is live on RouterPlex through both the OpenAI-compatible /v1/chat/completions endpoint and the Anthropic-compatible /v1/messages endpoint, so the same key reaches Opus 5, GPT-5.6, Gemini and the rest of the catalog.

Claude Opus 5 API pricing #

The headline number is that the price did not move. Opus 5 is positioned as a substantial capability step over Opus 4.8 while staying at the Opus-tier rate, which makes it the cheaper of the two on a cost-per-completed-task basis whenever it needs fewer retries or shorter agent runs.

Anthropic also offers a research-preview fast mode for Opus 5 at $10 input and $50 output per 1M tokens. That is a first-party Claude API feature, not part of the standard rate, and it is not available through third-party gateways.

See the live Claude Opus 5 API pricing page for the rate RouterPlex bills.

Claude Opus 5 specifications #

The model ID has no date suffix. Write claude-opus-5 exactly; a constructed ID like claude-opus-5-20260724 will fail.

Four API changes worth knowing before you migrate #

Most launch coverage stops at the benchmark chart. If you are moving an existing Opus 4.8 integration, these behavioural differences matter more than the scores.

Thinking is on by default. On Opus 4.8, omitting the thinking parameter meant the model did not think. On Opus 5, omitting it runs adaptive thinking. Because max_tokens caps thinking *and* response text together, a request that was sized tightly around its answer on Opus 4.8 can now truncate mid-response. Revisit max_tokens on any route that never set thinking.

Disabling thinking is capped at high effort. Sending thinking: {"type": "disabled"} together with effort of xhigh or max returns a 400. The combination is valid on Opus 4.8, so audit every call site rather than just the first one — effort and thinking are validated per request.

The full effort ladder is available. Opus 5 supports low through max with no beta header, and the lower rungs are unusually strong on this model. Effort defaults carried over from an older model are rarely the right setting; sweep it against your own evaluation rather than assuming high.

Prompt caching starts at 512 tokens. Opus 4.8 required a 1024-token prefix before a cache entry was created. Opus 5 halves that, so system prompts you had written off as too short to cache may now cache with no code change. At a $0.50 cache read against $5.00 standard input, that is worth re-checking.

Call Claude Opus 5 with RouterPlex #

The OpenAI-compatible shape works with any OpenAI SDK:

curl https://api.routerplex.com/v1/chat/completions \
  -H "Authorization: Bearer $ROUTERPLEX_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-opus-5",
    "messages": [
      {"role": "user", "content": "Trace this bug across the repository and name the root cause."}
    ]
  }'

Python uses the same base URL as every other model in the catalog:

import os
from openai import OpenAI
 
client = OpenAI(
    api_key=os.environ["ROUTERPLEX_KEY"],
    base_url="https://api.routerplex.com/v1",
)
 
response = client.chat.completions.create(
    model="claude-opus-5",
    messages=[{"role": "user", "content": "Review this migration plan for irreversible steps."}],
)
 
print(response.choices[0].message.content)

Use Claude Opus 5 in Claude Code #

Claude Opus 5 is reachable through the Anthropic-compatible /v1/messages endpoint, so Claude Code and the official Anthropic SDKs point straight at RouterPlex with no router or proxy in between:

export ANTHROPIC_BASE_URL=https://api.routerplex.com
export ANTHROPIC_AUTH_TOKEN=$ROUTERPLEX_KEY
export ANTHROPIC_MODEL=claude-opus-5

Thinking blocks, tool use and prompt caching all pass through in the native Anthropic format. The full walkthrough is in the Claude Code setup guide, and the billing comparison against a subscription is in Claude Code pricing.

Claude Opus 5 vs Opus 4.8, Fable 5 and Sonnet 5 #

Opus 5 and Opus 4.8 cost the same, so there is no pricing reason to stay on 4.8 — only the migration cost of re-testing the behavioural changes above. Fable 5 remains the escalation target when a task genuinely needs it, at double the rate.

Against Claude Sonnet 5, the gap is 2.5x on both input and output. For high-volume work where a cheaper model already succeeds, that difference compounds quickly.

Control Opus 5 spend before the first request #

At $25 per 1M output tokens, a long-running agent can consume a balance faster than expected — and thinking now being on by default means output token counts will be higher than the equivalent Opus 4.8 request. Three practical controls:

• Give the Opus 5 key its own hard budget so a runaway loop cannot drain the account balance.
• Set effort deliberately. Start lower than you think you need and raise it where evaluation shows a real difference.
• Reuse stable system prompts and tool definitions so the 512-token cache minimum can actually earn you the $0.50 cache-read rate.

Test it against a real task #

Pick a task where a better result has measurable value, then run the same input through Opus 5, Opus 4.8 and Sonnet 5. Compare correctness, review time and final billed cost rather than benchmark headlines — your prompt structure, tools and error tolerance decide which price-quality point wins.

Create a RouterPlex key with a hard budget, or compare Opus 5 with Claude Fable 5 and Kimi K3 through the same endpoint.