Claude Opus vs Sonnet: which model is right for you?
Claude Opus vs Sonnet comes down to the task: Sonnet suits daily work, while Opus 5.5 is for harder coding or reasoning where care matters more than speed.
Short answer: use Sonnet 5. It's the default model on Free and Pro for a reason, and for everyday writing, questions, and drafting it's not meaningfully worse than Opus. Switch to Opus 5.5 when you're deep in a hard coding problem, a long multi-step research task, or anything where a slower, more careful answer beats a fast one. Most people never need to switch at all.
This site isn't affiliated with Anthropic. Nobody's paying us to recommend one model over the other.
Lineup note, Oct 8, 2026: Anthropic's current models are Fable 5.1, Opus 5.5, Sonnet 5.5, and Haiku 5.5 (models overview). For launch details, read Claude Opus 5.5, Claude Sonnet 5.5, Claude Haiku 5.5, and Anthropic's Opus 5.5 launch note.
The one-breath verdict
| Default on Free and Pro | Sonnet 5 |
|---|---|
| Comparative latency | Sonnet 5.5: Fast, Opus 5.5: Moderate |
| API price per MTok (in/out) | Sonnet 5.5 $2/$10, Opus 5.5 $4/$20 |
| API context window | 1M tokens, both |
| API max output | 128K tokens, both |
| Best for | Sonnet: daily work. Opus: hard coding/reasoning |
The latency, price, context, and output rows come straight from Anthropic's models overview page, fetched October 8, 2026.
What actually changes when you switch
On the Claude Platform API, the two models share the same context window (1M tokens) and the same synchronous max output (128K tokens). Those are API specifications: claude.ai documents a 200K context window across consumer paid plans, with 500K on some Enterprise models. Opus does not get a larger window than Sonnet on the same surface.
Anthropic's own comparative-latency label is "Fast" for Sonnet 5.5 and "Moderate" for Opus 5.5. In practice that means Opus visibly takes longer per response, especially on anything non-trivial. One documented difference: Opus 5.5's adaptive thinking is always on and can't be turned off, per that same models page, while Sonnet 5.5 lets API users limit thinking to the steps between tool calls.
Cost scales the same direction. Opus 5.5 runs $4 input / $20 output per million tokens against Sonnet 5.5's $2/$10 , so 2x the price at standard API rates. That's irrelevant if you're just chatting on Free or Pro, but it matters the moment you're building something on the API.
Where Opus and Sonnet sit in Claude's lineup
"Opus" and "Sonnet" aren't the only two names in play, and it's easy to lose track of where each one sits. As of October 8, 2026, Anthropic's models overview lists four current models:
- Claude Haiku 5.5: the fastest tier, launched Oct 7, 2026, "for high-volume, latency-sensitive tasks such as classification, extraction, and routing." See Claude Haiku 5.5.
- Claude Sonnet 5.5: "the best combination of speed and intelligence," per Anthropic, released Sep 28, 2026. Sonnet 5, which became the Free and Pro default on June 30, 2026, is now listed as a legacy model, so check the model menu to see which Sonnet you're on.
- Claude Opus 5.5: built "for long-running agentic coding and knowledge work," released Sep 22, 2026. Slower and pricier than Sonnet by design.
- Claude Fable 5.1: positioned "for demanding reasoning and long-horizon agentic work." This is a separate, more expensive top tier ($10/$50 per MTok), not a fancier name for Opus. Most consumer chat users never touch it.
(There's also Mythos 5.1, a limited-availability model for organizations verified through Anthropic's programs, per its pricing page. It's out of scope for everyday use.)
The practical takeaway: Sonnet is the default and Opus is the option Anthropic positions for harder agentic coding and enterprise work. Fable and Haiku target different ends of the capability, latency, and usage spectrum.
How to switch Claude models and what plans allow
Click the model name
It sits next to the send button in claude.ai, showing whichever model you're currently on.
Pick from the list, or click "More models"
The default list shows a few options; "More models" reveals the full set, including Opus, Sonnet, and Haiku variants.
Send your next message
The switch applies starting with Claude's next response, mid-conversation. Same menu controls effort level and thinking mode.
Availability by plan: Free and Pro both default to Sonnet 5. Opus 4.8 is selectable on Pro and fully available on Max, which lets you pick from every current model. Team and Enterprise get the same model access as Pro/Max, seat-based, though admins can restrict specific models on Enterprise.
Anthropic doesn't publish a per-model message quota for Pro (for example, "N Opus messages per week") anywhere in its own docs, just a general weekly limit that applies across all models. See Claude usage limits for how that shared limit works, and treat any specific number you see elsewhere as an outside estimate, not an official figure. Full details on what each tier includes: Claude pricing explained.
Benchmarks, with a caveat
Anthropic's own Sonnet 5 vs. Opus 4.8 comparison ships as a chart image on its Sonnet 5 announcement, not as machine- readable numbers, so treat any exact percentage you see cited (including on this page) as reported by third parties rather than confirmed verbatim from Anthropic.
Directionally, Opus reportedly leads Sonnet on hard agentic and coding benchmarks like SWE-bench Pro by single digits, roughly in line with what you'd expect from a model that defaults to more careful, higher-effort reasoning. For anything you need to cite precisely, link the model announcement and its linked system card rather than a third-party aggregator.
Source-checked against platform.claude.com/docs and Anthropic's consumer plan documentation, July 2026.
If you're new to Claude generally
If you haven't settled into a workflow yet, the model question is a second-order decision. Start with how to use Claude to get the basics down, and check Claude pricing before you decide whether Pro or Max is worth it. If you're weighing Claude against ChatGPT more broadly, our comparison covers that separately from the model-picking question here.
Is Opus better than Sonnet?
Opus 5.5 is positioned for long-running agentic coding and knowledge work, but it's slower ("Moderate" latency vs. Sonnet 5.5's "Fast") and 2x the API price. "Better" depends on the task and should be tested with the same prompts and inputs.
Which Claude model does Claude choose by default?
Sonnet 5, on both the Free and Pro plans, since its June 30, 2026 release. Max and Team/Enterprise let you pick from the full model lineup, including Opus, without a fixed default.
Do I need Opus?
Probably not for daily use. Reach for it specifically on long, hard coding tasks or multi-step reasoning where a slower, more thorough answer is worth the wait. If you're not sure, start on Sonnet (the default) and switch only when you hit a task that feels like it needs more care.
Is Opus more expensive than Sonnet?
Yes, on the API: $4/$20 per million input/output tokens for Opus 5.5 versus $2/$10 for Sonnet 5.5, 2x the cost. On Free, Pro, or Max chat plans, there's no separate per-model charge, just your existing subscription and its shared usage limits.