Claude Opus 4.8 vs Claude Sonnet 4.6: Which Claude Model Should You Run?
Both models come from Anthropic and run on the Claude tooling stack. The real choice is whether Opus 4.8 delivers enough additional value on your hardest work to justify its price. Sonnet 5 is now the current baseline: it is the default on Claude Free and Pro and is available in Claude Code and the API.
The short answer
Pick Sonnet 5 first. It is Anthropic's default on Claude Free and Pro and is available in Claude Code and the API. Its introductory API price is $2 in / $10 out per million tokens through August 31, 2026, then $3/$15. Compare Opus 4.8 only on tasks hard enough to justify the premium, using repeatable evaluations on your own refactors and agent runs.
Start with Sonnet 5. Compare Opus 4.8 on your hardest agentic coding and long-horizon work, then route by measured quality, latency, and cost.
Where Claude Opus 4.8 wins
Opus 4.8 is the flagship, released May 28, 2026, and it is the best agentic coding model in the lineup. It plans before it edits and holds up over long autonomous runs, which is exactly where weaker models drift or lose the thread.
- Hardest agentic coding tasks: multi-file refactors and complex feature builds
- Planning before editing, so changes are deliberate rather than reactive
- Long autonomous runs where small quality gains compound across many steps
- Deep analysis over very large codebases and document sets using the full 1M-token window
Where Claude Sonnet 4.6 wins
Sonnet 5 is now Anthropic's default on Claude Free and Pro and is available through Claude Code and the API. Its introductory API price is $2 in / $10 out per million tokens through August 31, 2026, then $3/$15. Use it as the current comparison baseline and escalate only when your own coding evaluations justify the change.
- Everyday production assistant and RAG workloads
- Most coding tasks, where it clears the bar at a fraction of Opus pricing
- High-volume tool-using agents where per-token cost matters at scale
- Long-context analysis at the same 1M window, flat-rate, no surcharge
Pricing compared
Opus 4.8 runs $5 in / $25 out per million tokens, with a Fast Mode option at $10 / $50. Sonnet 4.6 runs $3 in / $15 out. On output, Opus costs roughly 1.7x more, and Fast Mode is more than 3x. Both support batch processing at 50% off and prompt caching up to 90% off cached input, so heavy RAG and repeated-context workloads get cheaper on either model.
If cost drives the decision, Sonnet 4.6 wins outright. Use batch and prompt caching on both to cut bills further, then reserve Opus for the work that actually needs it.
What they share
These are siblings, not rivals on everything. Both have a 1M-token context window at flat rates, web search, and image input. Neither generates images. Voice exists in the mobile apps but is not a core differentiator for either. Both get first-class Model Context Protocol support, since Anthropic created MCP, and both work in Claude Code, the dedicated CLI. The consumer tiers are the same: Free, Pro, and Max.
Fable 5 was restored globally on July 1, 2026 and can factor into a model evaluation where your plan and platform expose it. Mythos 5 is limited to approved Project Glasswing organizations, so exclude it unless your organization has that access.
Which to pick
Start with Sonnet 5 and only move when a specific task underdelivers. It is available in Claude Code and the API and is Anthropic's default on Claude Free and Pro. For long autonomous agents, deep multi-file refactors, production assistants, and RAG, compare Sonnet 5 with Opus 4.8 on your own quality and cost thresholds, then route by measured difficulty.
Specs at a Glance
| Claude Opus 4.8 | Claude Sonnet 4.6 | |
|---|---|---|
| Best for | Hardest agentic coding, long autonomous runs, planning before edits | Recommended default: production assistant, RAG, most coding |
| Context window | 1M tokens, flat rate | 1M tokens, flat rate |
| Flagship price (in/out per M) | $5 / $25 ($10 / $50 Fast Mode) | $3 / $15 |
| Image generation | No | No |
| Web search | Yes | Yes |
| Agentic coding | Best in class, strongest in lineup | Strong: 79.6% SWE-bench Verified |
| Free tier | Free, Pro, Max | Free, Pro, Max |
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