Source: ai-research/claude-code-docs-changelog-2026-09-25.md — changelog entry v2.1.280, September 22, 2026.
Claude Opus 5.5 (claude-opus-5-5) shipped 2026-09-22 in Claude Code v2.1.280. It is now the default Opus model, replacing Opus 5 (claude-opus-5). The headline change is a 20% price reduction: 20 per Mtok (vs. 25 for Opus 5), with $0.20/Mtok cache reads — a cache-read pricing tier that Opus 5 did not carry.
Key Takeaways
- Price drop vs. Opus 5: input cut from 4/Mtok (20% reduction); output cut from 20/Mtok (20% reduction). Cache reads now priced at $0.20/Mtok (vs. not listed for Opus 5).
- 1M context window — same as Opus 5. No regression on context capacity.
- Default Opus model from v2.1.280 onward. The
claudealias and Opus-pinned sessions resolve toclaude-opus-5-5. Explicitclaude-opus-5strings continue to route to the prior model. - Part of the
.5line pattern — follows the Fable 5.1 precedent: a point release on a-5generation at lower cost, without a separate capability announcement. No benchmarks were published at launch. - Capability unknown vs. Opus 5. The changelog gives pricing only. Community comparisons will determine whether
-5-5represents a quality change or a pure cost/delivery optimization.
Pricing Summary
| Metric | Opus 5.5 (claude-opus-5-5) | Opus 5 (claude-opus-5) |
|---|---|---|
| Input | $4/Mtok | $5/Mtok |
| Output | $20/Mtok | $25/Mtok |
| Cache reads | $0.20/Mtok | not listed |
| Cache writes | not listed | not listed |
| Context | 1M tokens | 1M tokens |
Pricing sourced from the v2.1.280 changelog entry (2026-09-22). Verify current pricing at anthropic.com/pricing.
Routing Guidance
For Claude Code sessions:
- Automatic: after v2.1.280, sessions without a pinned model use Opus 5.5 when the Opus tier is selected. No action needed.
- To pin Opus 5 explicitly (e.g., if a task depends on confirmed Opus 5 behavior): use
/model claude-opus-5or setANTHROPIC_MODEL=claude-opus-5for a session.
For API applications using claude-opus-5:
- The
claude-opus-5model ID continues to resolve to Opus 5. Routing does not change. - To adopt 5.5, update to
claude-opus-5-5. The cache-read pricing requires explicitly using the 5.5 model ID to benefit.
For API applications using the claude-opus-5 alias:
- The alias behavior was not specified in the v2.1.280 changelog. Verify against
api.anthropic.com/v1/modelsbefore relying on alias resolution.
Comparison to Prior Opus Models
| Model | Released | Input | Output | Context |
|---|---|---|---|---|
| Opus 5.5 | 2026-09-22 | $4/Mtok | $20/Mtok | 1M |
| Opus 5 | 2026-07-24 | $5/Mtok | $25/Mtok | 1M |
| Opus 4.8 | 2026-05-28 | $5/Mtok | $25/Mtok | 1M |
| Opus 4.7 | 2026-04-13 | $5/Mtok | $25/Mtok | 200K |
Open Questions
- Is Opus 5.5 materially different from Opus 5 on capability benchmarks? The changelog gives only pricing; no evals or qualitative notes were published alongside the v2.1.280 release.
- Cache-write pricing for Opus 5.5? The v2.1.280 entry lists $0.20/Mtok for cache reads but does not list a cache-write price. Confirm via the API pricing page.
- Does the Pro/Team Standard default switch from v2.1.280/v2.1.282 select Opus 5.5 specifically? Likely yes (it is the new default Opus model), but the changelog says “Sonnet to Opus” without specifying which Opus version.
Related
- Claude Opus 5 — predecessor model; full capability and benchmark details.
- What’s New — Week 39 — the release digest that covers this launch.
- Mythos 5 — frontier model in the same generation; Opus 5.5 is cheaper alternative.
- Model vs. Effort in Claude Code — routing framework for selecting between models.
- Opus 4.7 Best Practices — older routing guidance; the effort/cost tradeoff principles still apply to Opus 5.5.