Claude Opus 5 shipped on the 24th of July, 2026, as claude-opus-5
. It's priced at $5 per million input tokens and $25 per million output tokens — the same as Opus 4.8, and half of what Fable 5 costs.
The context window is 1M tokens long, the max output is 128K. And there's one breaking change: the model thinks by default now. In other words, on the older Opus you had to ask for thinking explicitly, and it's now set up so it thinks on its own automatically.
Now it's allocating thinking depth per turn itself depending on the set effort level; the higher the effort, the more it thinks, but you can still set it explicitly in the request, and the parameter itself hasn't changed — thinking: {"type": "adaptive"}
is still valid and still means the default. This means that when migrating a project that didn't do any thinking just by renaming it to this new Opus, you need to make sure you have enough room for both the thinking and the visible part of its response, so raise max_tokens
.
Also, if you disable thinking — which you can now do only at high effort or below, because pairing it with xhigh or max returns a 400 — it may output a call to a tool as plain text instead of emitting a proper tool_use
block, or leak some of its internal tags into the output. So they recommend keeping it enabled and controlling the cost via the effort level instead.
It's priced at $5 per million input tokens and $25 per million output tokens, just like Opus 4.8. The price didn't move, but capability did. Fable 5 is $10 and $50 for the same volumes, so this is exactly half.
There's also fast mode — a separate pricing line, and a research preview that's been running since February (fast-mode-2026-02-01
), on Opus 4.8 as well. It's available only through the Claude API; it's not on Amazon Bedrock, Google Cloud or Microsoft Foundry. It's priced at $10 per million input tokens and $50 per million output tokens, so 2x the price for up to 2.5x the output tokens per second (for the record this is throughput, not time to first token, so don't expect end-to-end latency to halve).
The minimum length a prompt needs to be to be cacheable is now 512 tokens instead of 1024, so prompts that were too short to get cached before are being cached automatically now.
Opus 5 is half the price of Fable 5, and they're very close in terms of the numbers, so for most use cases it's usually about the price. According to their benchmarks:
These are Anthropic's figures, so take them with a grain of salt; they're grading themselves. But generally speaking — mid-tier is no longer a compromise pick, and if you were to use Fable 5 by default, it's worth reconsidering in light of these numbers.
One place it doesn't win is exploit development. While on OSS-Fuzz it finds vulnerabilities about as well as Mythos 5, writing the exploits is scored separately — and there it's far behind.
The effort level starts at high by default; it's the default level both on the Claude API and for Claude Code, and this is what Anthropic document as a starting point. There are five levels in total — low, medium, high, xhigh and max — and in terms of this new Opus, it's more important than ever to choose the right one, as this model translates more effort into better output than any previous Opus, so it makes more of a difference which level you pick.
We'd recommend testing yourself and adjusting up or down from high based on these results — lower when the quality is good enough to save time and money, higher for the hardest tasks. It's also worth noting that especially in this model, the two lowest levels are actually really capable, so the quality there is really good for a fraction of the cost, and the code review is very decent even at the lower levels.
On the other hand, if you're planning to use the top two levels, make sure to set max_tokens
high enough, 64K is a good place to start; you need it to have space for both thinking and acting across tools and subagents. Stream the responses rather than awaiting one of them.
The context window is 1M tokens long, and that's both its size and the max. It's not 200k long, this figure is about the client app; update it if possible. It's a single size, so you can't have reduced variants.
If you change the model to Opus 5, apart from renaming it, you need to update the surrounding configuration. The biggest potential pitfall is a prompt scaffolding that you might have left behind from older models — the model self-validates out of the box, so any leftover lines like "add a final verification step" or "use a subagent to verify" are prompting it to do additional verification now. Make sure to remove them. Two things simply aren't available on this Opus: web fetch and Priority Tier. If you're relying on either, that's a blocker rather than something you configure around.
If you're an agent-infra maintainer, there are also 2 new features for you (both behind beta headers at the moment):
`mid-conversation-tool-changes-2026-07-01`
)`server-side-fallback-2026-07-01`
) — Claude API only, and explicitly not supported on Microsoft FoundryIf you change the model to this new Opus, you may notice a few differences in terms of behaviour even if you haven't changed anything in your prompts:
None of these are bugs, they're all steerable by prompting. If you feel like the new Opus is slower or noisier than the previous one after the name change, make sure to check if it's not one of these differences before concluding that the model must've regressed; the "thoughtful and proactive" part of their description is the same thing from their side of the fence.
In terms of its actual capabilities:
In terms of the day 1 plan:
max_tokens
, as now it needs to accommodate thinking too; it's the most likely reason your output gets cut off after the switchAnd perhaps most importantly: run your own code against it, not their benchmarks, and not ours either — although they could be a good start. We recently published a runnable benchmark with Kimi K3, Fable 5 and Opus 4.8 already hooked up. It contains a TypeScript ledger seeded with real bugs, with hidden tests and a prompt to benchmark the models against.