Claude Opus 4.8 vs GPT-5.6 Luna — Price, Context, and Capability Compared
Claude Opus 4.8 vs GPT-5.6 Luna: which should I use?
Claude Opus 4.8 costs 4.4× more per blended million tokens than GPT-5.6 Luna. GPT-5.6 Luna has the larger context window (1,000,000 tokens). Default to GPT-5.6 Luna unless you specifically need Claude Opus 4.8's edge. Only Claude Opus 4.8 exposes an extended-thinking mode.
Price, speed, and task evidence
Task verdict
Best-fit task signals from the published model strengths; this is not a substitute for a controlled benchmark.
| Fact | Claude Opus 4.8 | GPT-5.6 Luna |
|---|---|---|
| Best fit | Complex, multi-step tasks where Fable 5’s premium isn’t justified. | High-volume, latency-sensitive tasks like classification, extraction, and chat. |
| Reasoning mode | Available | Unavailable |
Effective workload cost
Modeled for Coding Agent: 20,000 input + 2,000 output tokens per task, 1 turn. This is a workload model, not a provider quote.
| Fact | Claude Opus 4.8 | GPT-5.6 Luna |
|---|---|---|
| Coding Agent / task | $0.15 (modeled) | $0.03 (modeled) (winner) |
| Input / output rate | $5.00 / $25.00 per M | $1.00 / $6.00 per M |
Speed
Only non-estimated benchmark results are shown as measured.
| Fact | Claude Opus 4.8 | GPT-5.6 Luna |
|---|---|---|
| Measured throughput | 58 tokens/s | 126 tokens/s (winner) |
| Time to first token | 470 ms | 300 ms |
API compatibility
Provider-level wire-format and SDK facts; model-specific parameter differences may still apply.
| Fact | Claude Opus 4.8 | GPT-5.6 Luna |
|---|---|---|
| OpenAI SDK | Not drop-in | Usable |
| Request shape | Messages API — system prompt is a top-level field, not a message role, and max_tokens is required on every call. | Canonical /chat/completions and /responses shape — every OpenAI-compatible provider on this site imitates it. |
| Streaming | SSE (Anthropic content-block events) | SSE (OpenAI delta) |
Privacy and retention
Provider policy and residency facts from the verified provider registry. A missing retention policy is not treated as a guarantee.
| Fact | Claude Opus 4.8 | GPT-5.6 Luna |
|---|---|---|
| Provider says API data trains models | No | No |
| Published retention period | Unavailable | Unavailable |
| Data residency | Unavailable | US by default; EU data residency available on enterprise agreements |
Migration effort
Direction is from each displayed model to the other. Effort is derived from provider compatibility and published parameter maps.
| Fact | Claude Opus 4.8 | GPT-5.6 Luna |
|---|---|---|
| Move Claude Opus 4.8 → GPT-5.6 Luna | config; 3 breaking parameter differences | Target: GPT-5.6 Luna |
| Move GPT-5.6 Luna → Claude Opus 4.8 | Source: GPT-5.6 Luna | code-change; 8 breaking parameter differences |
| Why | Keep the `openai` SDK; change `baseURL` and the API key. | Messages API — system prompt is a top-level field, not a message role, and max_tokens is required on every call. |
Spec comparison
| Claude Opus 4.8 | GPT-5.6 Luna | |
|---|---|---|
| Price (input) | $5.00/M | $1.00/M ✓ |
| Price (output) | $25.00/M | $6.00/M ✓ |
| Blended price | $10.00/M | $2.25/M ✓ |
| Context window | 500,000 tokens | 1,000,000 tokens ✓ |
| Max output | 64,000 tokens | 64,000 tokens |
| Modalities | text, vision | text, vision |
| Reasoning mode | Yes | No |
| Released | 2026-04 | 2026-06 |
| Speed | 58 t/s | 126 t/s ✓ |
Cost at scale (3:1 blended)
| Tokens / month | Claude Opus 4.8 | GPT-5.6 Luna | Delta |
|---|---|---|---|
| 1,000,000 | $10.00 | $2.25 | $7.75 (4.4×) |
| 10,000,000 | $100.00 | $22.50 | $77.50 (4.4×) |
| 100,000,000 | $1000.00 | $225.00 | $775.00 (4.4×) |
Choose Claude Opus 4.8 if…
- ✓Elite coding and multi-step reasoning
- ✓Strong instruction following on ambiguous prompts
- ✓Extended-thinking mode
- ✓Complex, multi-step tasks where Fable 5’s premium isn’t justified.
Choose GPT-5.6 Luna if…
- ✓Cheapest current GPT-5.6 tier
- ✓Low latency for high-volume calls
- ✓1M context window and vision input
- ✓High-volume, latency-sensitive tasks like classification, extraction, and chat.
Run this exact matchup right now
Send the same prompt to Claude Opus 4.8 and GPT-5.6 Luna side by side and see the outputs yourself.
Try Claude Opus 4.8 vs GPT-5.6 Luna FreeFAQ
Is Claude Opus 4.8 cheaper than GPT-5.6 Luna?
GPT-5.6 Luna is cheaper, at $2.25 per million blended tokens vs $10.00 for Claude Opus 4.8.
Which has the bigger context window, Claude Opus 4.8 or GPT-5.6 Luna?
GPT-5.6 Luna has the larger context window: 1,000,000 tokens vs 500,000.
Can Claude Opus 4.8 replace GPT-5.6 Luna for coding?
Both are viable for coding. Elite coding and multi-step reasoning (Claude Opus 4.8) vs Cheapest current GPT-5.6 tier (GPT-5.6 Luna) — pick based on which strength matters more for your workload.
Which is faster, Claude Opus 4.8 or GPT-5.6 Luna?
GPT-5.6 Luna is faster: 126 t/s vs 58 t/s, measured on our speed benchmarks.
Neither of these? See Claude Opus 4.8 alternatives or GPT-5.6 Luna alternatives.
Related
Pricing verified 2026-06-07. Specs verified 2026-08-14.