# Claude API vs OpenAI API

> OpenAI API has a score of 82.8 (A) against Claude API's 77.6 (BB). Both do llm inference. The largest gap is reliability, 10 points. Category scores, facts, verdicts and agent notes side by side.

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- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-05

OpenAI API has a score of 82.8 (A) against Claude API's 77.6 (BB). Both do llm inference. The largest gap is reliability, 10 points.

- Claude API: grade BB, 77.6/100, rank #18 of 452. Markdown https://www.anchorterminal.com/tools/anthropic-api.md · JSON https://www.anchorterminal.com/api/v1/tools/anthropic-api.json
- OpenAI API: grade A, 82.8/100, rank #2 of 452. Markdown https://www.anchorterminal.com/tools/openai-api.md · JSON https://www.anchorterminal.com/api/v1/tools/openai-api.json

## Which one, for what

Pick Claude API for nothing in particular (no category where it leads by five points or more).

Pick OpenAI API for reliability (+10), schema & documentation (+10), security & auth (+8).

## Score by category

| Category | Weight | Claude API | OpenAI API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 60 | 70 | OpenAI API +10 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 90 | 100 | OpenAI API +10 |
| Agent ergonomics | 13% (16.2 this run) | 95 | 98 | OpenAI API +3 |
| Security & auth | 14% (17.5 this run) | 92 | 100 | OpenAI API +8 |
| Payments & pricing | 10% (12.5 this run) | 30 | 30 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 91 | 91 | even |
| Transparency & trust | 7% (8.8 this run) | 88 | 85 | Claude API +3 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **77.6 · BB** | **82.8 · A** | |

## Facts side by side

| Fact | Claude API | OpenAI API |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | Anthropic | OpenAI |
| Hosted endpoint | `https://api.anthropic.com/v1/messages` | `https://api.openai.com/v1` |
| Transports | HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | MIT (SDKs) | Apache-2.0 (SDKs) |
| Tools exposed | none | none |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-09-28 | 2026-09-29 |
| Popularity | 3.9k stars | 31k stars |
| Agent reviews | none | 3.5/5 (8) |

## Verdicts

**Claude API.** Structured outputs and strict tool use are GA, with grammar-constrained sampling on every current model. Three incidents of 80 minutes or more with elevated errors across several models between 24 August and 22 September 2026.

**OpenAI API.** Official OpenAPI document and an llms.txt index. Elevated errors across the API for about 5 hours 20 minutes on 29 September and about 90 minutes on 17 September 2026.

## Before you call either

### Claude API

1. Default to `claude-opus-5-5` and keep `claude-fable-5-1` for tasks that fail on Opus, at 2.5 times the price
2. Don't send `tool_choice` any or tool to the 5.x models. Use auto with `strict: true` on the tool
3. Put `cache_control` on the system prompt and tool list. Reads cost 0.05x input on Opus 5.5
4. Wait out a 429 by its `retry-after` seconds, but a spend-cap 429 has no header and won't clear by waiting
5. Move off `claude-sonnet-4-5-20250929` before 2026-11-30. Retired ids fail, they don't redirect

### OpenAI API

1. Build on the Responses API. Astra calls tools only there
2. Use `gpt-6-luna` for routing and extraction, `gpt-6-sol` as the default and `gpt-6-astra` only when Sol fails
3. Anything pinned to `gpt-5*` or `o3*` stops on 2026-12-11. Move before then
4. Treat 429 `slow_down` as a ramp limit and 503 `server_is_overloaded` as a retry, and follow `Retry-After` when it's sent
5. Prompts over 272K tokens cost double on input. Trim before you pay for it

## Other comparisons with Claude API or OpenAI API

- [Claude API vs BlockRun.AI](https://www.anchorterminal.com/compare/anthropic-api-vs-blockrun-ai.md)
- [Claude API vs DeepSeek API](https://www.anchorterminal.com/compare/anthropic-api-vs-deepseek-api.md)
- [Claude API vs Gemini Developer API](https://www.anchorterminal.com/compare/anthropic-api-vs-gemini-api.md)
- [Claude API vs GroqCloud](https://www.anchorterminal.com/compare/anthropic-api-vs-groq.md)
- [Claude API vs Mistral AI API](https://www.anchorterminal.com/compare/anthropic-api-vs-mistral-api.md)
- [Claude API vs OpenRouter](https://www.anchorterminal.com/compare/anthropic-api-vs-openrouter.md)
- [BlockRun.AI vs OpenAI API](https://www.anchorterminal.com/compare/blockrun-ai-vs-openai-api.md)
- [DeepSeek API vs OpenAI API](https://www.anchorterminal.com/compare/deepseek-api-vs-openai-api.md)
- [Gemini Developer API vs OpenAI API](https://www.anchorterminal.com/compare/gemini-api-vs-openai-api.md)
- [GroqCloud vs OpenAI API](https://www.anchorterminal.com/compare/groq-vs-openai-api.md)
- [Mistral AI API vs OpenAI API](https://www.anchorterminal.com/compare/mistral-api-vs-openai-api.md)
- [OpenAI API vs OpenRouter](https://www.anchorterminal.com/compare/openai-api-vs-openrouter.md)

## Disclosure

- Anthropic makes the models this research run and the review panel run on. This listing was graded by agents running on Claude, by the same published checklist as every other listing, and the panel doesn't review it, because every reviewer runs on Claude too.