Claude Opus 5.5 vs Opus 5 and 4.8: is switching worth it

Update, October 2026. Claude Opus 5 (claude-opus-5) and Opus 4.x (claude-opus-4.8, claude-opus-4.7, claude-opus-4.6) are currently unavailable in Zukko. Current model list: the Models page↗ or GET https://api.zukko.pro/v1/models. Closest replacement: claude-opus-5-5 (Claude Opus 5.5).

claude-opus-5-5 (Claude Opus 5.5) is the current flagship of the Anthropic-compatible catalog, with vision, extended thinking, and a 1,000,000-token context window. claude-opus-5, claude-opus-4.8, 4.7 and 4.6 have been switched off in the catalog — a request to them returns 503 model_disabled — so the question is no longer "which version to keep" but "how to move to Opus 5.5 and make sure the results work for you".

How to compare when the old version is gone

On the stated feature set Opus 5.5 is on par with Opus 5 and 4.8: images, extended thinking, a million-token context. You can no longer run the same task through the old version, so the honest approach is to compare Opus 5.5's answers with saved Opus 5 or 4.8 answers on the same prompts, and use claude-sonnet-5 as a second live point of comparison. Look at two numbers: request cost and answer quality for your specific job.

curl https://api.zukko.pro/v1/models/info | jq '.data[] | select(.id | startswith("claude-opus"))'

That shows current pricing and limits without spending a single token: Opus 5.5 on Zukko is $0.30/$0.30 per 1M input/output tokens versus the official $4/$20 (Sonnet 5 is the same $0.30/$0.30 versus the official $2/$10).

Comparing with extended thinking turned on

For the kind of work Opus usually earns its price on — hard multi-step logic, code review, planning — it makes more sense to compare models with thinking enabled rather than in short-answer mode:

import requests

KEY = "fetch_your_key"
TASK = "Find the logical bug in this load-balancing algorithm: ..."

for model in ["claude-opus-5-5", "claude-sonnet-5"]:
    resp = requests.post(
        "https://api.zukko.pro/v1/messages",
        headers={
            "Authorization": f"Bearer {KEY}",
            "anthropic-version": "2023-06-01",
        },
        json={
            "model": model,
            "max_tokens": 2048,
            "thinking": {"type": "enabled", "budget_tokens": 4000},
            "messages": [{"role": "user", "content": TASK}],
        },
        timeout=180,
    )
    print(model, resp.headers.get("X-Zukko-Cost-Micros"))

Check the cost of a request with extended thinking through the X-Zukko-Cost-Micros header — it already reflects the final price of that specific call, thinking tokens included, with no need to compute it yourself separately.

Counting tokens before sending

The Anthropic-compatible mode gives you a free way to check request size ahead of time without spending balance:

curl https://api.zukko.pro/v1/messages/count_tokens \
  -H "Authorization: Bearer fetch_your_key" \
  -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{"model":"claude-opus-5-5","messages":[{"role":"user","content":"..."}]}'

This matters most when the context gets close to a million tokens: before paying for the request itself, it's worth confirming it fits the limit at all, and knowing its real size in tokens rather than characters.

If your prompt was tuned for 4.8 or Opus 5

A newer version doesn't necessarily behave the same way on a prompt tuned for the old one. If 4.8 or Opus 5 reliably delivered what you needed, run the same set of tasks through Opus 5.5 before moving production and compare against the saved answers; if the results diverge, adjust the prompt or test claude-sonnet-5 on your own tasks (same $0.30/$0.30 price on Zukko). Swapping the id blindly without that check spends budget with no guaranteed payoff.

What a request to a switched-off version returns

claude-opus-5 and claude-opus-4.8 are already switched off, and instead of an answer you get 503 with the code model_disabled (not a 404 and not model_retired):

{"error": {
  "code": "model_disabled"
}}

Don't count on a replacement named in the error text — check the current GET https://api.zukko.pro/v1/models list; for Opus the closest replacement is claude-opus-5-5. Just handle that code the same way you handle any other API error, and keep the model id in config rather than hard-coded.

Key limits and caching for repeated tests

If the comparison stretches over several days, it's worth setting up a separate key with a daily spending limit just for testing — configurable on the key's page in the dashboard — so the Opus 5.5 experiment doesn't blend into production spend and quietly eat the shared budget. And if the same prompt gets run repeatedly to check answer stability, turn on caching with the X-Zukko-Cache: true header (not via temperature: 0: Claude models may reject a temperature other than 1 with a 400) — then a repeat request with a fully identical body comes back instantly and for free (and isn't written to /v1/usage), flagged X-Zukko-Cache: hit — handy for telling it apart from an actual new model call when reading through comparison logs.

When the task needs fresh data, not just a stronger model

Extended thinking on Opus 5.5 deepens reasoning over what's already in the prompt, but it doesn't add access to current events. If the answer needs to rely on data that wasn't part of the model's training, use the separate POST /v1/web-search endpoint — it's built specifically for models without built-in search, and choosing between Opus 5.5 and Sonnet 5 doesn't change that.

Before switching all production traffic

If Opus 5.5 does at least as well as before on your test prompts, it's smarter to route a portion of real traffic through it first rather than switching every production request at once. Comparing on live data shows faster whether the results actually hold up outside curated test cases.

The practical takeaway

Move production based on results from testing your own tasks, not because a new number showed up in the name. /v1/models/info gives you price at no cost, /v1/messages/count_tokens gives you exact request size for free too, and running a couple dozen representative prompts through Opus 5.5 (and Sonnet 5 for comparison) with extended thinking enabled will show whether Opus 5.5 fits your specific job.